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Metals are present in nearly all aspects of modern life. Iron, classified as a heavy metal, contributes to 90% of all refined metals. Aluminum, a light metal, is the next most commonly refined metal. Some metals and metal alloys exhibit remarkable structural strength per unit mass, making them valuable materials for supporting heavy loads or withstanding impact damage. Metal alloys can be engineered to have high resistance to shear, torque, and deformation. However the same metal that provides strength and resilience may be susceptible to fatigue from repeated use or sudden stress failure when surpassing its load capacity. Despite these considerations, the robustness and flexibility of metals have led to their widespread application in the construction of high-rise buildings and bridges, as well as in the manufacturing of vehicles, appliances, tools, pipes, and railroad tracks.

For example, the automotive industry is one of the largest markets for steel industry. Therefore, it must fulfill some specific requirements like enhancing the fuel efficiency and reducing the vehicle mass without sacrificing current strength and stiffness of the steels. Young’s modulus and internal friction data are key elements to investigate the defect interaction during the different manufacturing processes and their influence on the mechanical properties.
Without undergoing rigorous quality inspection, these metal materials may be inadequately chosen or utilized, resulting in premature material failure and, more critically, posing a risk of major safety incidents.

Publications

Impulse Excitation Internal Friction Study of Retained Austenite in Ferrous Martensite.
Authors:

Kim, J. H., Ju, Y. N., Kang, S., & De Cooman, B. C. (2018). Metallurgical and Materials Transactions A 49(11), 5235-5240.

Abstract:

Internal friction (IF) measurements were conducted using ferrous lath martensite specimens with different retained austenite fractions. While a distinctive Snoek-Kê-Köster (SKK) peak was detected in the IF spectra, the peak shape did not conform to the peak shape observed for fully martensitic steel. Peak analysis suggests that the peak shape is related to the overlap of the SKK peak with a Finkelstein–Rosin peak, additional Debye-type peak related to the retained austenite.

High Temperature Elastic Properties of Reduced Activation Ferritic-Martensitic (RAFM) Steel Using Impulse Excitation Technique.
Authors:

Tripathy, H., Raju, S., Hajra, R. N., & Saibaba, S. (2018). Metallurgical and Materials Transactions A 49(3), 979-989.

Abstract:

The polycrystalline elastic constants of an indigenous variant of 9Cr-1W-based reduced activation ferritic-martensitic (RAFM) steel have been determined as a function of temperature from 298 K to 1323 K (25 °C to 1000 °C), using impulse excitation technique (IET). The three elastic constants namely, Young’s modulus E, shear modulus G, and bulk modulus B, exhibited significant softening with increasing temperature, in a pronounced non-linear fashion. In addition, clearly marked discontinuities in their temperature variations are noticed in the region, where ferrite + carbides → austenite phase transformation occurred upon heating. Further, the incidence of austenite → martensite transformation upon cooling has also been marked by a step-like jump in both elastic E and shear moduli G. The martensite start Ms and Mf finish temperatures estimated from this study are, Ms = 652 K (379 °C) and Mf =580 K (307 °C). Similarly, the measured ferrite + carbide → austenite transformation onset (Ac1) and completion (Ac3) temperatures are found to be 1126 K and 1143 K (853 °C and 870 °C), respectively. The Poisson ratio μ exhibited distinct discontinuities at phase transformation temperatures; but however, is found to vary in the range 0.27 to 0.29. The room temperature estimates of E, G, and μ for normalized and tempered microstructure are found to be 219 GPa, 86.65 GPa, and 0.27, respectively. For the metastable austenite phase, the corresponding values are: 197 GPa, 76.5 GPa, and 0.29, respectively. The measured elastic properties as well as their temperature dependencies are found to be in good accord with reported estimates for other 9Cr-based ferritic-martensitic steel grades. Estimates of θelD, the elastic Debye temperature and γG, the thermal Grüneisen parameter obtained from measured bulk elastic properties are found to be θelD = 465 K (192 °C) and γG = 1.57.

The in-situ mechanical spectroscopy and electric resistance study of WE43 magnesium alloy during aging.
Authors:

Knapek, M., Minárik, P., Trojanová, Z., Kubásek, J., Hajek, M., Šmilauerová, J., … & Stráská, J. (2018). Journal of Alloys and Compounds 743, 646-653.

Abstract:

The WE43 magnesium alloy was studied by mechanical spectroscopy and electric resistance measurements in-situ during aging at 210 and 250 °C. Isothermal aging up to 196 h at these temperatures promotes only minor increase in the Young’s modulus (0.4–2.5%). The mechanical spectroscopy results correlate with the resistance measurements and are discussed with respect to the precipitation sequence in this material. Furthermore, during heating up to 450 °C, the mechanical spectroscopy measurements identified an internal friction peak at ∼350 °C which is brought about by the relaxation at interfaces between the semicoherent and incoherent precipitates and the matrix. Height of the peak is dependent on the material thermal history.

Comparison Of The Damping Properties Of The Compressor Valve Steels At Different Frequencies.
Authors:

ElBsat, M. N., Wenzel, M. J., Asmus, M. J., Renovich, F., Misbrener, R., & Kummer, J. P. (2018).

Abstract:

The flapper valve is one of the most critical components of the reciprocating compressor. During the compressor’s service lifetime, the flapper valve has to open and close billions of times without failure or maintenance. Smooth and efficient operation of the compressors not only requires an optimized design of the valve but it also places high demands on its material. Material damping of the flapper valves in the reciprocating compressors positively influences the flapper valve operation by directly reducing the magnitude of the induced stress waves in the valve reeds. It has also been reported in several studies that material damping reduces the amplitude of fatigue stresses in components or specimens subjected to fatigue load conditions. The current study presents an investigation of the material damping properties of a range of hardened and tempered martensitic steels including the new flapper valve steel grade, Flap-X, developed by voestalpine Precision Strip AB. The tested materials included three flapper valve steel grades Flap-X, AISI 420 (SS716) and AISI 1095 (20C) along with two other thin strip materials: the S-Coat L+ tool steel and 13Cr 0.7C martensitic stainless steel grade known as UHB AEB-L. Material damping was measured using impulse excitation apparatus that measured the resonant frequencies and the loss rate of vibrations in the flexural mode in order to evaluate the material damping parameter (Q -1 ) at room temperature. Different frequencies were investigated in this study ranging from 50 Hz to approximately 10 kHz for all the tested materials. The measured material damping data for the tested materials showed that damping decreased with increasing frequency above 50 Hz up to around 2000 Hz and then stabilized until approximately 9000Hz. Material damping for the Flap-X grade was found to be higher than the SS 716 grade at all the measured frequencies and higher than all the tested grades at ~9000 Hz. The material damping of the 20 C grade was found to be the highest at 50 Hz while the UHB AEB-L grade displays the highest damping at 250 Hz and 2000 Hz. In addition, an attempt has been successfully made to fit the Rayleigh damping model to the obtained damping data. These results have significant implications for the impact fatigue stresses in the valves, their impact fatigue life and the noise levels they contribute to in the reciprocating compressors.

Measurement of high temperature elastic moduli of an 18Cr-9Ni-2.95 Cu-0.58 Nb-0.1 C (Wt%) austenitic stainless steel.
Authors:

Tripathy, H., Hajra, R. N., Sudha, C., Raju, S., & Saibaba, S. (2018, April). AIP Conference Proceedings (Vol. 1951, No. 1, p. 020009). AIP Publishing

Abstract:

The Young’s modulus (E) and Shear modulus (G) of an indigenously developed 18Cr-9Ni-0.1C-2.95 Cu-0.58Nb (wt %) austenitic stainless steel has been evaluated in the temperature range 298 K to 1273 K (25 °C to 1000 °C), using Impulse excitation technique (IET). The Bulk modulus (K) and the poison’s ratio have been estimated from the measured values of E and G. It is observed that the elastic constants (E, G and K) are found to decrease in a nonlinear fashion with increase in temperature. The Cu precipitation is found to influence the elastic moduli of the steel in the cooling cycle. The observed elastic moduli are fitted to 3rd order polynomial equations in order to describe the temperature dependence of E, G, K moduli in the temperature range 298-1273 K (25 °C to 1000 °C). The room temperature values of E,G and K moduli is found to be 207, 82 and 145 GPa respectively for the present steel.

Evaluation of fatigue performance of additively manufactured SS316 via internal damping.
Authors:

Haghshenas, A., & Khonsari, M. M. (2018). Manufacturing letters 18, 12-15

Abstract:

Additively manufactured (AM) specimens made of stainless steel 316 are tested using the impulse excitation technique (IET) and their damping characteristics are correlated to fatigue life. Results reveal that the damping value is inversely proportional to the fatigue life of the specimens. It is also shown that the procedure enables one to determine the onset of crack initiation and thus provides a viable approach for monitoring the integrity of AM parts.

Thermo-mechanical Material Characterization and Stretch-bend Forming of AA6016.
Authors:

Odenberger, E. L., Caro, L. P., Åhlin, H., & Oldenburg, M. (2018, September). IOP Conference Series: Materials Science and Engineering (Vol. 418, No. 1, p. 012022). IOP Publishing.

Abstract:

Lightweight design has become increasingly in focus for the manufacturing industry. Global environmental challenges, goals and legislations imply that lighter and sustainable products are imperative to remain competitive. One example is stamped products made of aluminum alloys which are of interest to the automotive industry, where lightweight designs are essential. In order to increase formability and to produce more complex geometries in stamped aluminum components there is a need to develop hot forming techniques. The Finite Element Method (FEM) has enabled important advances in the study and design of competitive manufacturing procedures for metal parts. Predicting the final geometry of a component is a complex task, especially if the forming procedure occurs at elevated temperatures. This work presents selected results from thermo-mechanical material testing procedures, FE-analyses and forming validation tests in AA6016 material. The material tests are used to determine the thermo-mechanical anisotropic properties, strain rate sensitivity and formability (Forming Limit Curves, FLC) at temperatures up to 490°C. Stretch-bending tests are performed to compare predicted results with experimental observations such as punch force, strain levels, thinning, forming temperatures, springback and failure. It was found that the heat-treatment and forming at elevated temperatures substantially increased formability and that measured responses could in general be predicted if care was taken to model the initial blank temperatures, heat transfer and thermo-mechanical material properties. The room temperature case confirms the importance of considering anisotropy.

Formability study of the third generation automotive medium-Mn steel.
Authors:
Zheng, G., Chang, Y., Li, X., Wang, C., & Dong, H. (2018, August). In 2018 IEEE International Conference on Mechatronics and Automation (ICMA) (pp. 661-665).
Abstract:

Medium-Mn steel is an outstanding representative of the newly developed third-generation advanced automotive steels. In our previous experimental studies, industrial trial production of 0.1C–5Mn medium-Mn steel has been realized, anti-decarburization ability of warm-formed medium-Mn steel has been assessed compared with the conventional hot-formed 22MnB5 steel, and heterogeneous spot-welding performance evaluation has also been completed on the industrial production line. Previous results proved that the medium-Mn steel have a development trend of replacing hot-formed boron steel in the automotive industry. Besides, numerical simulation analysis on the forming process of an actual automotive part is also an important topic of the applicability research of medium-Mn steel. Therefore, in this paper, a warm-formed medium-Mn steel B-pillar part was investigated by simulation in order to elucidate the effects of process parameters. Firstly, mechanical property tests were carried out to obtain the material parameters for establishing an accurate finite element model of the B-pillar part. After that, the warm-forming process was simulated and the effectiveness of the simulation was validated by benchmarking with the experimental result. Finally, the deep drawing zone with maximum fracture risk was focused to analyze the sensitivity of process parameters including initial blank temperature (IBT), blank holding force (BHF), and forming velocity (FV). Research results show that the IBT has the greatest influence on the thickness of the deep drawing zone. The recommended IBT is between 450 and 550 °C, which is favorable to obtain higher total elongation without loss of strength. This study is helpful to provide a theoretical basis for the large-scale application of warm-forming medium-Mn steel.

Effect of the free surface on the fatigue crack front curvature at high stress asymmetry.
Authors:
Oplt, T., Hutar, P., Pokorný, P., Náhlík, L., Chlup, Z., & Berto, F. (2019). International Journal of Fatigue 118, 249-261.
Abstract:

The purpose of this paper is to investigate the effect of the vertex singularity on the fatigue crack front behaviour. Single edge notch bend specimens of steel EA4T and aluminium alloy 7075 of various thicknesses are subjected to the cyclic loading and the angles of the fatigue crack front curvature was measured. The experimental procedure is simulated using finite element analysis. Two methodologies used for the fatigue crack front shape estimation are compared. One is using stress singularity exponent as a controlling parameter and the second one is using stress intensity factor. Both methodologies provide comparable results of crack front formation process and they are in very good agreement with experimental results.

Influence of substitution of Fe by Co on structural and magneto-mechanical properties of Fe-27Ga alloy.
Authors:
Jen, S. U., Bobrikov, I. A., Balagurov, A. M., Shih, C. Y., Cheng, W. C., Emdadi, A., … & Golovin, I. S. (2018). Materials Science and Engineering: B 236, 76-83.
Abstract:

Fe55Co19Ga26 alloy was made in an induction furnace, and then slowly cooled to room temperature (RT). The structural property of the as-cast alloy was examined by an x-ray diffractometer. From the diffraction pattern, we conclude that the alloy contains the A2 and D03 phases at room temperature. The magnetic hysteresis loop was measured by the vibration sample magnetometer: saturation magnetization MS = 123 emu/g, and coercivity HC = 22 Oe. The mechanical properties, such as Young’s modulus (E) and shear modulus (G), were measured as a function of magnetic field (H) up to H = 3 KOe, respectively, by the impulse excitation of vibration (IEV) method. The ΔE or ΔG effect is defined as ΔE/E = [ES – E0]/E0, or ΔG/G = [GS – G0]/G0, where subscript “s” means the saturation state, and the subscript “0” means the zero-field state. Moreover, the flexural magneto-mechanical coupling coefficient (KE) and the torsional magneto-mechanical coupling coefficient (KG) were calculated from: (KE)2/[1 – (KE)2] = ΔE/E0 and (KG)2/[1 – (KG)2] = ΔG/G0. Thus, KE = 22% and KG = 19% for the slowly-cooled Fe55Co17Ga28 alloy.

Cyclic stress responses of a newly developed nickel-base superalloy at elevated temperatures.
Authors:
Cui, L., Yu, J., Liu, J., & Sun, X. (2019). Journal of Alloys and Compounds 773, 250-263.
Abstract:

Total strain-controlled low cycle fatigue tests were conducted on the newly designed nickel-base superalloy M951G under different testing conditions; the relationship among cyclic stress responses, microstructural degradations, deformation mechanisms and testing conditions has been established. Results show that both the cyclic hardening and softening behaviors are dependent on the testing temperature and strain amplitude. As the strain amplitude increases both at 900 and 1000 °C, M951G alloy exhibits cyclic hardening under low strain amplitudes and cyclic softening under higher strain amplitudes. At 900 °C, the initial cyclic hardening is related to the coherent γ/γ′ interface, parallel dislocation arrays and dislocation bypassing the tiny γ′ particles. At higher strain amplitudes, the initial cyclic softening is due to the higher density of shearing dislocations in γ′ precipitates. At 1000 °C, plenty of parallel dislocation arrays present in γ channels, which reduces the possibility of dislocation interactions from different slip systems and results in initial cyclic hardening. Under higher strain amplitudes, apart from microstructural degradations, dislocations shearing into γ′ precipitates and formation of dislocation networks, the dislocation annihilation and partial loss of coherency of γ′ precipitates are also responsible for the initial cyclic softening at 1000 °C.

Thermal aging effects on microstructure, elastic property and damping characteristic of a eutectic Sn–3.5 Ag solder.
Authors:
Gain, A. K., & Zhang, L. (2018). Journal of Materials Science: Materials in Electronics 29(17), 14519-14527.
Abstract:

This paper describes the changes in microstructures and their effects on property degradations in an environmentally friendly eutectic [Formula presented].7Cu (wt.%) solder alloy when subjected to harsh service conditions. A thorough microscopy investigation was conducted by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and diffraction analysis with transmission electron microscopy (TEM). In the as-received alloy Cu6Sn5 intermetallic compound (IMC) particles are dispersed in the grain interiors and grain boundaries of β-Sn matrix. When the alloy was exposed for 60 days at 150 °C, the size of Cu6Sn5 IMC particles and Sn matrix grains were increased significantly. As a result the mechanical reliability of electronic interconnections turned inferior. This was confirmed by measuring a range of electrical and mechanical properties that include electrical resistivity, Young’s moduli, shear moduli, microhardness and nano indentation creep behaviour. A comparison between the as-received and age-treated alloy shows that the degradation in Young’s and shear moduli was about 10.6 and 9.9%, respectively, and that in hardness was about 25%. However the age treatment improved the damping property of the alloy.

Effects of Ni nanoparticles addition on the microstructure, electrical and mechanical properties of Sn-3Ag-0.5 Cu solder alloy Sn-Ag-Cu alloy.
Authors:
Gain, A. K., & Zhang, L. (2019). Materialia 100234
Abstract:
The effects of Ni nanoparticles addition on the microstructure, electrical resistivity and mechanical properties such as elastic/shear moduli, microhardness and creep of Sn-3.0Ag-0.5Cu (SAC305; in wt.%) electronic interconnect materials have been investigated. Microstructure analysis of Sn-3.0Ag-0.5Cu-0.5 Ni nanoparticles (in wt.%) solder revealed that adding Ni nanoparticles has promoted the formation and growth of (Cu, Ni)-Sn intermetallic compound (IMC) in the bulk phase of the samples and the structure of composite material resulted refined. This finer structure and (Cu, Ni)-Sn IMCs in a composite solder resulted in improved mechanical and electrical properties with respect to the Sn-3Ag-0.5Cu reference alloy. Indeed, a comparison between the reference alloy and composite material doped with 0.5 wt.% Ni nanoparticles indicates that the improvement in elastic and shear modulus was 8% and 11.2%, respectively, whereas the microhardness value was increased about 16.7%. Moreover, in the electronic interconnect systems on organic solderability preservative (OSP)-Cu pad, a scallop-shaped Cu6Sn5 IMC was detected at their interfaces at early stage reaction. Increasing the reaction time, the growth of the Cu6Sn5 and the formation of a very thin Cu3Sn IMC layer was observed. However, in Sn-3.0Ag-0.5Cu-0.5 Ni nanoparticles composite material, a very stable (Cu, Ni)-Sn IMC grew at the interface between composite solder and (OSP)-Cu pad in absence of Cu3Sn IMC. In addition, a relatively fine Ag3Sn and (Cu, Ni)-Sn IMC appeared to be evenly dispersed in β-Sn matrix and the fine microstructure surely affect the overall properties of solder joints.
High-temperature and humidity change the microstructure and degrade the material properties of tin silver interconnect material.
Authors:
Gain, A. K., & Zhang, L. (2018). Microelectronics Reliability 101-110.
Abstract:
The present work elucidates the microstructural changes and their impact on electrical resistivity and mechanical behavior of Sn-3.5 wt% Ag electronic interconnect material after exposure at high-temperature and relative humidity (85 °C/85%) environment. An in-depth structural observation is performed through electron microscopy e.g., SEM, EBSD and TEM techniques. The microstructural analysis shows that the as-received sample contained sub-micron size ε-Ag3Sn intermetallic compound (IMC) and dendritic structure having a special orientation 〈100〉60° relationship with the matrix grains. However, it is found that after exposing the material at the harsh service environment for 60 days, the morphology, and size of the matrix grains and the ε-Ag3Sn IMC phase are significantly altered. Such microstructural changes impact negatively on their material properties e.g., electrical resistivity, elastic and shear moduli, hardness and creep performance. An assessment between the as-cast and the aged material demonstrated that the degradations in hardness and elastic modulus are approximately 21.8 and 31.7%, respectively. Subsequently, the heat-treated material displays a higher temperature and strain amplitude-dependence damping characteristic as compared to the as-cast solder material.
A Comparative Study on Formability of the Third-Generation Automotive Medium-Mn Steel and 22MnB5 Steel.
Authors:
Zheng, G., Li, X., Chang, Y., Wang, C., & Dong, H. (2018). Journal of Materials Engineering and Performance 27(2), 530-540.
Abstract:
Medium-Mn steel is an outstanding representative of the newly developed third-generation advanced automotive steels. In our previous experimental studies, industrial trial production of 0.1C–5Mn medium-Mn steel has been realized, anti-decarburization ability of warm-formed medium-Mn steel has been assessed compared with the conventional hot-formed 22MnB5 steel, and heterogeneous spot-welding performance evaluation has also been completed on the industrial production line. Previous results proved that the medium-Mn steel have a development trend of replacing hot-formed boron steel in the automotive industry. Besides, numerical simulation analysis on the forming process of an actual automotive part is also an important topic of the applicability research of medium-Mn steel. Therefore, in this paper, a warm-formed medium-Mn steel B-pillar part was investigated by simulation in order to elucidate the effects of process parameters. Firstly, mechanical property tests were carried out to obtain the material parameters for establishing an accurate finite element model of the B-pillar part. After that, the warm-forming process was simulated and the effectiveness of the simulation was validated by benchmarking with the experimental result. Finally, the deep drawing zone with maximum fracture risk was focused to analyze the sensitivity of process parameters including initial blank temperature (IBT), blank holding force (BHF), and forming velocity (FV). Research results show that the IBT has the greatest influence on the thickness of the deep drawing zone. The recommended IBT is between 450 and 550 °C, which is favorable to obtain higher total elongation without loss of strength. This study is helpful to provide a theoretical basis for the large-scale application of warm-forming medium-Mn steel.
Damage accumulation and crack initiation detection based on the evolution of surface roughness parameters.
Authors:
Haghshenas, A., & Khonsari, M. M. (2018). International Journal of Fatigue, 107, 130-144.
Abstract:
Cyclic strain localization generates sharp surface slip markings in the form of depressions and elevations on the surface of materials. The process gives rise to the formation of persistent slip bands and results in immanent changes that manifest themselves in the form of surface roughening. The heights and depths of these extrusions and intrusions grow during cyclic loading up to a critical value leading to crack initiation. In this study, we investigate the evolution of the surface roughness parameters starting from pristine specimens and ending in final fracture in fully-reversed cyclic bending tests. Results are presented for both low-and high-cycle fatigue that covers a wide range of surface finish. Two types of contacting (via a stylus) and no-contacting (optical) profilometers were used in this investigation. The most sensitive and useful surface roughness parameter for the assessment of fatigue growth in low-and high-cycle fatigue is identified, and it is shown that results can be utilized to detect the onset of fatigue crack nucleation. For this purpose, a surface roughness criterion for detecting crack initiation at different applied loads is introduced.
Isolated and modulated effects of topology and material type on the mechanical properties of additively manufactured porous biomaterials.
Authors:
Hedayati, R., Ahmadi, S. M., Lietaert, K., Pouran, B., Li, Y., Weinans, H., … & Zadpoor, A. A. (2018). Journal of the Mechanical Behavior of Biomedical Materials.
Abstract:

In this study, we tried to quantify the isolated and modulated effects of topological design and material type on the mechanical properties of AM porous biomaterials. Towards this aim, we assembled a large dataset comprising the mechanical properties of AM porous biomaterials with different topological designs (i.e. different unit cell types and relative densities) and material types. Porous structures were additively manufactured from Co-Cr using a selective laser melting (SLM) machine and tested under quasi-static compression. The normalized mechanical properties obtained from those structures were compared with mechanical properties available from our previous studies for porous structures made from Ti-6Al-4V and pure titanium as well as with analytical solutions. The normalized values of elastic modulus and yield stress were found to be relatively close to each other as well as in agreement with analytical solutions regardless of material type. However, the material type was found to systematically affect the mechanical properties of AM porous biomaterials in general and the post-elastic/post-yield range (plateau stress and energy absorption capacity) in particular. To put this in perspective, topological design could cause up to 10-fold difference in the mechanical properties of AM porous biomaterials while up to 2-fold difference was observed as a consequence of changing the material type.

On the plasticity mechanisms of lath martensitic steel
Authors:
Jo, K. R., Seo, E. J., Sulistiyo, D. H., Kim, J. K., Kim, S. W., & De Cooman, B. C. (2017). Materials Science and Engineering: A,, 704, 252-261.
Abstract:

The plasticity mechanisms of press hardening steel with a fully lath martensite microstructure were examined experimentally by strain rate sensitivity measurements, repeated relaxation tests and internal friction measurements. The analysis of relaxation tests suggests that the micro-plasticity could be due to the motion of mobile non-screw dislocations, based on mobile dislocation exhaustion observed in the micro-plastic range. In the macro-plastic range, the plasticity is thought to be due to the generation of mobile screw dislocations. The solute carbon-dislocation interaction results in a negative strain rate sensitivity and a Snoek-Köster-Kê peak in the internal friction spectrum of the lath martensitic press hardening steel. The magnitude of the effective activation volume and its stress dependence indicate that plastic deformation is most likely controlled by screw dislocation motion by formation and lateral movement of kink pairs dragging solute carbon atom atmospheres. Both isotropic and kinematical hardening seem to play a role in the strain hardening behavior of lath martensitic steel.

Utilizing Low‐Cost Eggshell Particles to Enhance the Mechanical Response of Mg–2.5 Zn Magnesium Alloy Matrix.
Authors:
Parande, G., Manakari, V., Kopparthy, S. D. S., & Gupta, M. (2017). Advanced Engineering Materials.

Abstract:

The search for lightweight high-performance materials is growing exponentially primarily due to ever-increasing stricter environmental regulations and stringent service conditions. To cater to these requirements, the use of low-cost reinforcements has been explored in the Mg matrix to develop Economically Conscious Magnesium (ECo–Mg) composites. In this study, eggshell particles (3, 5, and 7 wt%) reinforced Mg–Zn composites are synthesized using blend-press-sinter powder metallurgy technique. The results reveal that the addition of eggshell particles enhances microhardness, thermal stability, damping, and yield strength with an inappreciable change in the density. In particular, Mg2.5Zn7ES composite do not ignite till ≈750 °C. The overall combination of properties exhibited by Mg–Zn–ES composites exceeds many of currently used commercial alloys in the transportation sector. An attempt is made, in this study, to interrelate microstructure and properties and to study the viability of compression and ignition properties with a comparison to commercially used Mg alloys.
Effect of Carbon on the Damping Capacity and Mechanical Properties of Thermally Trained Fe-Mn Based High Damping Alloys.
Authors:
Choi, W. S., & De Cooman, B. C. (2017). Materials Science and Engineering: A.
Abstract:
The effect of C on the damping and mechanical properties of thermally trained Fe-17 wt.-%Mn-X wt.-%C (0<X<0.06) high-damping alloys was analyzed by the impulse internal friction technique and uniaxial tensile tests. The alloys were subjected to a combination of thermo-mechanical processing and thermal cycling which resulted in a C content independent phase fraction and grain size of ɛ-martensite and γ-austenite. The ɛ↔γ phase transformation and the anti-ferromagnetic transition in the γ-phase were observed in the temperature-dependent damping and modulus measurements, respectively. While C had no influence on the intrinsic internal friction of the γ-phase, small amounts of C significantly reduced the damping associated with the motion of ɛ-γ interface boundaries and the widening of stacking faults by the movement of partial dislocations. The C content at which these relaxation processes were suppressed, i.e. approximately 0.03 wt.-%C, coincided with the onset of dynamic strain aging as inferred from the appearance of serrations on the flow curves.
The effect of grain size on the damping capacity of Fe-17wt% Mn.
Authors:
Shin, S., Kwon, M., Cho, W., Suh, I. S., & De Cooman, B. C. (2017). Materials Science and Engineering: A , 683, 187-194.
Abstract:
The grain size dependence of the damping capacity of Fe-17wt%Mn steel was investigated. A high damping capacity was measured in the ultra-fine grained steel, despite its lower volume fraction of ε martensite and lower density of ε variant boundaries and ε/γ phase boundaries. Dilatometry of the ultra-fine grained Fe-17wt%Mn steel revealed that the ε↔γ phase transformation was largely suppressed. The features of the damping spectra were related to the anti-ferromagnetic transition in the γ phase, the thermo-elastic ε↔γ phase transformation and the motion of grain boundaries in the ultra-fine grained microstructure. The damping spectrum of the ultra-fine grained Fe-17wt%Mn steel was dominated by grain boundary damping effects.
Lanthanum effect on improving CTE, damping, hardness and tensile response of Mg-3Al alloy.
Authors:
Kumar, A., Meenashisundaram, G. K., Manakari, V., Parande, G., & Gupta, M. (2017). Journal of Alloys and Compounds , 695, 3612-3620.
Abstract:
In the present study, Mg-3Al-xLa (x ∼ 1, 2.5, 4) alloys were synthesized using disintegrated melt deposition technique followed by hot extrusion. These alloys were critically investigated for microstructure, tensile and compression properties, damping properties, microhardness and fracture morphology. The grain size of Mg-3Al was significantly reduced by the addition of Lanthanum (La) and it was minimum for 2.5 La-containing alloy (∼5.8 μm, 25% of pure Mg grain size). SEM and X-ray studies revealed the suppression of β-eutectic phase ( ) due to the formation of , , and intermetallic phases. Microhardness increased with the addition of La and it was recorded highest for Mg-3Al-4La (122 Hv). Mechanical characterization results show that the tensile yield strength (TYS), ultimate tensile strength (UTS) and ductility for Mg-3Al-2.5La alloy are the best reported values till date among all the available reports for this system of alloy (TYS ∼ 160 MPa, UTS ∼ 249 MPa and fracture strain ∼22%). Results of damping measurement revealed an increase in damping of Mg-3Al alloy due to the presence of La (2.5%). Compression results show that the addition of La to Mg-3Al caused gradual decrease in compression yield strength and elongation.
Behaviour of the Young's modulus at the magnetocaloric transition in La (Fe, Co, Si) 13.
Authors:
Kaeswurm, B., Barcza, A., Vögler, M., Geiger, P. T., Katter, M., Gutfleisch, O., & Cohen, L. F. (2017). Journal of Alloys and Compounds , 697, 427-433.
Abstract:
Magnetic solid state cooling applications require families of samples where the magnetic transition is cascaded across the working range of the fridge. Although magnetic properties are widely studied, information relating to the mechanical properties of such systems is less prevalent. Here we study the mechanical properties of a series of magnetocaloric La(Co,Fe,Si)13 samples where the Co content is varied to produce a range of transition temperatures. It was found that at room temperature the flexural strength decreases and the Young’s modulus increases with increasing Co content. Interestingly we find a significant reduction of Young’s modulus at temperature around the magnetic transition temperature. This reduction was less pronounced with increasing Co content. We associate the softening with the magnetovolume coupling known to exist in these materials.
Growth mechanism of intermetallic compound and mechanical properties of nickel (Ni) nanoparticle doped low melting temperature tin–bismuth (Sn–Bi) solder.
Authors:
Gain, A. K., & Zhang, L. (2016). Journal of Materials Science: Materials in Electronics, 27(1), 781-794.
Abstract:
This paper investigates the effects of Ni nanoparticles on the formation of intermetallic compound (IMC) layers and mechanical properties of low melting temperature Sn–58Bi (wt%) based solders on copper (Cu) substrate. At the initial reaction for the plain Sn–Bi solder/Cu substrate system, an island-shaped Cu6Sn5 IMC layer was found to adhere at the substrate surface. A very thin Cu3Sn IMC layer was also observed between the Cu6Sn5 IMC layer and Cu substrate as the reaction time increased. However, in the composite solders doped with Ni nanoparticles, a scallop-shaped ternary (Cu, Ni)–Sn IMC layer appeared at the interface without Cu3Sn IMC layer. In the solder ball region, the Bi phase with bright contrast was homogeneously distributed in the β-Sn matrix. After adding the Ni nanoparticles, an additional very fine Sn–Ni IMC particle was found to have been distributed in the β-Sn matrix. The IMC layer thicknesses were increased with the reaction time and temperature. However, the IMC growth behavior of composite solder was slower than that of the plain solder system. Furthermore, the mechanical properties of the composite solder exhibited higher values than that of the plain Sn–Bi solder due to the strengthening effect of fine Sn–Ni IMC particles.
The Effect of Grain Size on the Damping Capacity of Fe-17wt% Mn.
Authors:
Shin, S., Kwon, M., Cho, W., Suh, I. S., & De Cooman, B. C. (2016). Materials Science and Engineering: A.
Abstract:
The grain size dependence of the damping capacity of Fe-17wt%Mn steel was investigated. A high damping capacity was measured in the ultra-fine grained steel, despite its lower volume fraction of ε martensite and lower density of ε variant boundaries and ε/γ phase boundaries. Dilatometry of the ultra-fine grained Fe-17wt%Mn steel revealed that the ε↔γ phase transformation was largely suppressed. The features of the damping spectra were related to the anti-ferromagnetic transition in the γ phase, the thermo-elastic ε↔γ phase transformation and the motion of grain boundaries in the ultra-fine grained microstructure. The damping spectrum of the ultra-fine grained Fe-17wt%Mn steel was dominated by grain boundary damping effects.
Variation and consistency of Young’s modulus in steel.
Authors:
Chen, Z., Gandhi, U., Lee, J., & Wagoner, R. H. (2016). Journal of Materials Processing Technology, 227, 227-243.
Abstract:
The mechanically-measured Young’s modulus of metals is consistently lower than the physically measured one, particularly after plastic straining. Furthermore, the nominally elastic loading and unloading behavior is not linear; it shows significant curvature and hysteresis. While many reports of this so-called “modulus effect” have appeared, the consistency of the behavior among grades of steel, or within a single grade produced by alternate methods and suppliers, is unknown. That is, there is little information on whether it is necessary for manufacturers to measure and control the mechanical modulus for every coil of steel in order to guarantee accurate simulations, consistent forming, and reliable in-service behavior. In order to address these issues, 12 steels (4 diverse grades: IF, HSLA, DP600, DP980; 3 producers per grade) were subjected to high-precision modulus measurements using mechanical testing, resonant frequency damping analysis, and ultrasonic pulse-echo techniques. All of these measurements show remarkable consistency among not only suppliers but also among grades. The primary determinant of hysteresis/curvature of the stress–strain response was found to be the nominal flow stress of the alloy. Other variations of overall mechanical modulus are minor compared with hysteresis/curvature. The following conclusions were reached: 1) there is no significant difference among suppliers of a single steel grade, 2) there is very little difference between grades of steel, except for that attributable to differing strengths, 3) mechanical unloading and reloading after pre-strain are similar, 4) cyclic loading and unloading cycles have no accumulated effect except through a minor change of flow stress, and 5) the initial loading or unloading modulus is very similar to the physical modulus, but the mechanically measured slope degrades very rapidly as loading or unloading proceeds, and plateaus at even small strain (<2%). The measured unloading and reloading behavior is more consistent and reproducible than that during initial loading, and unloading behavior is more consistent and reproducible than reloading behavior. Therefore, it is recommended that unloading after pre-strain is used to represent all of nominally elastic nonlinear behavior most accurately.
Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy.
Authors:
Watson, T. J., Gordillo, M. A., Cernatescu, I., & Aindow, M. (2016).Scripta Materialia, 123, 51-54.
Abstract:
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion-strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300˚C.
Magnetic and magneto-mechanical properties of Fe 55 Co 19 Ga 26 alloy.
Authors:
Jen, S. U., Cheng, W. C., Lin, Y. C., Chen, Y. Z., & Golovin, I. S. (2016). Materials Letters, 182, 72-74.
Abstract:
Fe55Co19Ga26 alloy was made in an induction furnace, and then slowly cooled to room temperature (RT). The structural property of the as-cast alloy was examined by an x-ray diffractometer. From the diffraction pattern, we conclude that the alloy contains the A2 and D03 phases at room temperature. The magnetic hysteresis loop was measured by the vibration sample magnetometer: saturation magnetization MS = 123 emu/g, and coercivity HC = 22 Oe. The mechanical properties, such as Young’s modulus (E) and shear modulus (G), were measured as a function of magnetic field (H) up to H = 3 KOe, respectively, by the impulse excitation of vibration (IEV) method. The ΔE or ΔG effect is defined as ΔE/E = [ES – E0]/E0, or ΔG/G = [GS – G0]/G0, where subscript “s” means the saturation state, and the subscript “0” means the zero-field state. Moreover, the flexural magneto-mechanical coupling coefficient (KE) and the torsional magneto-mechanical coupling coefficient (KG) were calculated from: (KE)2/[1 – (KE)2] = ΔE/E0 and (KG)2/[1 – (KG)2] = ΔG/G0. Thus, KE = 22% and KG = 19% for the slowly-cooled Fe55Co17Ga28 alloy.
Internal friction analysis of lath martensite in press hardened steel.
Authors:
Sulistiyo, D. H., Cho, L., Seo, E. J., & De Cooman, B. C. (2016). Materials Science and Technology, 1-14.
Abstract:
Internal friction (IF) measurements were carried out on a press hardened steel (PHS) after continuous annealing, press hardening and bake hardening. The IF peaks of the PHS with a lath martensite microstructure were analysed by comparison with previously published data. This was supplemented by comparison with the IF spectra of the same steel with a ferrite–pearlite microstructure after deformation at room temperature, and after recrystallisation annealing and quenching. The relation between the IF peaks of PHS, and the γ-peak, Snoek peak and Snoek-Kê-Köster peak observed for ferritic steel is discussed.
Internal-friction analysis of dislocation–interstitial carbon interactions in press-hardened 22MnB5 steel.
Authors:
Choi, W. S., Lee, J., & De Cooman, B. C. (2015). Materials Science and Engineering: A, 639, 439-447.
Abstract:
The dislocation–point defect interactions in press hardened 22MnB5 steel were characterized by the impulse internal friction technique. The analysis focused on the interaction between the interstitial carbon and the dislocation in the as-die quenched lath martensite and the effect of the paint-baking process on the carbon/dislocation interaction. The results showed that whereas the paint-baking affected the dislocation-enhanced Snoek peak, the Snoek-Kê-Köster peak was unaffected by the aging processes occurring during paint baking. A deformation carried out after the paint-baking resulted in the enhancement of the dislocation-enhanced Snoek peak.
Evolution of the elastic modulus of Zr–Cu–Al BMGs during annealing treatment and crystallization: Role of Zr/Cu ratio.
Authors:
Idriss, M., Célarié, F., Yokoyama, Y., Tessier, F., & Rouxel, T. (2015). Journal of Non-Crystalline Solids, 421, 35-40.
Abstract:
In this study, the Young’s modulus (E) and the internal friction (Q− 1) of bulk metallic glasses ZrxCu(90 − x)Al10 for x = 45, 50, 55 and 60 were measured. Using a technique of resonant frequency and damping analysis, these parameters were measured in real time from room temperature up to 800 °C. Two kinds of thermal treatment were performed: i) below Tg over several days in order to analyze the annealing treatment; ii) above Tg with increasing temperature at a constant rate in order to characterize the crystallization process. The evolution of E is discussed and has revealed interesting information concerning the structure modification during thermal treatments. After the crystallization treatment, phase characterization measurements of the samples were performed using the X-ray diffraction technique. The crystallized phases and their influences on the evolution of the Young’s modulus are discussed as a function of the Zr/Cu ratio.
Studies on Dynamic Elastic and Internal Friction Properties of Cu-Cr-Zr-Ti Alloy Between 25 and 650° C.
Authors:
Saravanan, K., Sharma, V. M. J., Asraff, A. K., Narayanan, P. R., Sharma, S. C., & George, K. M. (2015). Journal of Materials Engineering and Performance, 24(12), 4721-4727.
Abstract:
In the present study, dynamic elastic constants namely Young’s modulus, shear modulus, Poisson’s ratio, and internal friction properties for polycrystalline Cu-0.68Cr-0.04Zr-0.03Ti-0.015Fe (wt.%) alloy have been evaluated from 25 to 650 °C temperature in argon environment. These properties were determined using resonance-based high-temperature impulse excitation technique. The temperature-dependent elastic constants are very vital for the thermo-structural analysis to predict the performance of the component/structure. The test results revealed that, the alloy exhibits linear reduction in Young’s modulus and shear modulus with increasing temperature. On the other hand, the calculated Poisson’s ratio showed minor increase with temperature. It was shown that, the variation in the internal friction is attributed to in situ aging in the temperature range studied. Overaging beyond 500 °C has led to drastic increase of internal friction. This has been supported by hardness measurement, tensile test, differential scanning calorimetry test, and transmission electron microscopy examination.
Inverse characterization method for mechanical properties of strain/strain-rate/temperature/temperature-history dependent steel sheets and its application for hot press forming.
Authors:
Kim, H., Kim, D., Ahn, K., Yoo, D., Son, H. S., Kim, G. S., & Chung, K. (2015). Metals and Materials International, 21(5), 874-890.
Abstract:
In order to measure the flow curves of steel sheets at high temperatures, which are dependent on strain and strain rate as well as temperature and temperature history, a tensile test machine and specimens were newly developed in this work. Besides, an indirect method to characterize mechanical properties at high temperatures was developed by combining experiments and its numerical analysis, in which temperature history were also accounted for. Ultimately, a modified Johnson-Cook type hardening law, accounting for the dependence of hardening behavior with deterioration on strain rate as well as temperature, was successfully developed covering both pre- and post-ultimate tensile strength ranges for a hot press forming steel sheet. The calibrated hardening law obtained based on the inverse characterization method was then applied and validated for hot press forming of a 2-D mini-bumper as for distributions of temperature history, thickness and hardness considering the continuous cooling transformation diagram. The results showed reasonably good agreement with experiments
Structural, magneto-mechanical, and damping properties of slowly-cooled polycrystalline Fe 81 Ga 19 alloy.
Authors:
Jen, S. U., Cheng, W. C., & Chiang, F. L. (2015). Journal of Alloys and Compounds, 651, 544-550.
Abstract:
In this study, we discussed the structural, magneto-mechanical, and damping properties of slowly-cooled polycrystalline Fe81Ga19 alloy. From the X-ray diffraction, transmission electron microscopy, and optical microscopy studies, we conclude that the alloy contains the disordered A2 and ordered D03 phases. Due to the D03 precipitation hardening effect, the yield strength (Y) of slowly-cooled Fe81Ga19 is about 950 MPa, much higher than that (about 500 MPa) of [100] single crystal Fe81Ga19. For the first time, both Young’s modulus (E) and shear modulus (G) were measured vs. magnetic field (H) up to 3 kOe by the impulse excitation of vibration method successfully: the ΔE and ΔG effects. The magneto-mechanical (flexure) coupling factor (KE) of the alloy, estimated from the ΔE effect, is 11.7%, and the (torsion) coupling factor (KG), from the ΔG effect, is 19.1%. The damping capacity, estimated by considering the magneto-elastic hysteresis mechanism alone, is 0.0076 only. The experimentally found total damping capacity is about 0.01–0.03. The latter should be larger than the former, because there are additional micro- and macro-eddy-current contributions to the total damping capacity.
A porous TiAl6V4 implant material for medical application.
Authors:
Deing, A., Luthringer, B., Laipple, D., Ebel, T., & Willumeit, R. (2014). International journal of biomaterials, 2014.
Abstract:
Increased durability of permanent TiAl6V4 implants still remains a requirement for the patient’s well-being. One way to achieve a better bone-material connection is to enable bone “ingrowth” into the implant. Therefore, a new porous TiAl6V4 material was produced via metal injection moulding (MIM). Specimens with four different porosities were produced using gas-atomised spherical TiAl6V4 with different powder particle diameters, namely, “Small” (<45 μm), “Medium” (45-63 μm), “Mix” (90% 125-180 μm + 10% <45 μm), and “Large” (125-180 μm). Tensile tests, compression tests, and resonant ultrasound spectroscopy (RUS) were used to analyse mechanical properties. These tests revealed an increasing Young’s modulus with decreasing porosity; that is, “Large” and “Mix” exhibit mechanical properties closer to bone than to bulk material. By applying X-ray tomography (3D volume) and optical metallographic methods (2D volume and dimensions) the pores were dissected. The pore analysis of the “Mix” and “Large” samples showed pore volumes between 29% and 34%, respectively, with pore diameters ranging up to 175 μm and even above 200 μm for “Large.” Material cytotoxicity on bone cell lines (SaOs-2 and MG-63) and primary cells (human bone-derived cells, HBDC) was studied by MTT assays and highlighted an increasing viability with higher porosity.
Determination of elastic and damping properties for clossed-cell aluminium foams using Impulse Excitation Technique.
Authors:
Voiconi, T., Marsavina, L., Linul, E., & Kováčik, J. (2014). Proceedings of XIIIth Youth Symposyum of Experimental Solid Mechanics, 141-145.
Abstract:
The damping behavior of metallic foams is excellent. This attribute can be useful in applications in lightweight structures to overcome noise and vibration problems. This paper presents an experimental investigation for determination of elastic and damping properties for ductile aluminum foam (AlMg1Si0.6) produced by the powder metallurgy method. The Resonant Frequency and Damping Analyzer (RFDA), which is a non-destructive testing device to determine the resonant frequency of materials, were used to perform the experiment. Tests were carried out on rectangular bar samples with skin, having density in range 0.5 to 0.6 g/cm3. If the sample shape, dimensions and mass are known the Young’s Modulus and Shear Modulus are calculated from the fundamental flexural resonant frequency (out of plane flexure) and torsional resonant frequency according to ASTM E 1876. Internal friction coefficient (Q-1) can be also calculated according with f r – Frequency [Hz] and k – Loss rate [1/s].
Magnesium powder injection moulding for biomedical application.
Authors:
Wolff, M., Schaper, J. G., Dahms, M., Ebel, T., Kainer, K. U., & Klassen, T. (2014). Powder Metallurgy, 57(5), 331-340.
Abstract:
Currently, commercial biodegradable implants are mainly made from degradable polymers, such as polyglycolic acid or polylactide acid (PLA). These polymer implants, produced by injection moulding technique, suffer from long degradation times between 18 and 36 months, poor mechanical properties and acidic degradation behaviour. On the other hand, magnesium alloys are drawing increasing interest as biodegradable medical implant material for orthopaedic applications in bone tissue; thus, a replacement of polymers by Mg would be attractive. The production of biomedical and biodegradable Mg alloy parts and implants by powder metallurgy and metal injection moulding (MIM) respectively offers the opportunity for economic manufacturing of parts with mechanical properties matching those of cortical bone tissue, as well as the provision of porous surface structures beneficial for cell ingrowth and vascularisation. Furthermore, the technique guarantees a homogenous microstructure being crucial for a predictable degradation process. This study shows how magnesium powder can be processed successfully by MIM. Recent magnesium alloy implant prototypes and tensile test specimen, produced by MIM technique, provide strength and stiffness twice as high compared to modern polymer based implants. Ultimate tensile strength (UTS) of 131 MPa, yield strength of 64 MPa, residual porosity of 2-6% and elastic modulus of 46 GPa, measured by dynamic method, were achieved under application of special sintering technique and sintering atmosphere control. The paper is focussing on sintering methods and porosity control and measurement.
Elastic strain energy induced by epsilon martensitic transformation and its contribution to the stacking-fault energy of austenite in Fe–15Mn–xC alloys.
Authors:
Lee, S. J., Han, J., Lee, C. Y., Park, I. J., & Lee, Y. K. (2014). Journal of Alloys and Compounds, 617, 588-596.
Abstract:
The elastic strain energy and its contribution to the stacking-fault energy (SFE) of γ austenite were quantitatively investigated as a function of the C concentration in Fe–15Mn–(zero to 0.37)C (wt.%) alloys. The elastic strain energy was evaluated in both the homogeneous and inhomogeneous states using measured values for molar volume change, strain, and the elastic properties, which are affected by the γ to ε martensitic transformation. Both the molar volume change and the strain decreased with increasing C concentration, primarily due to the reduction in lattice contraction along the c-axis of the ε phase. The addition of C decreased the room-temperature elastic moduli of the alloys with a dual-phase microstructure of γ and ε. The elastic moduli of the ε phase decreased more rapidly with increasing C concentration than did the elastic moduli of the γ phase. Both the homogeneous and inhomogeneous strain energy values exponentially decreased with increasing C concentration. These values were similar because of the insignificant difference in the shear modulus between the γ and ε phases. The contribution of each energy term to the SFE decreased in the following order: chemical, interfacial, elastic strain, and magnetic energies. Whereas the magnetic energy has been considered for calculating the SFE, the elastic strain energy has been neglected until now. Accordingly, we realized that the elastic strain energy should be considered for more accurate SFE calculation, particularly for Fe-high Mn alloys with C concentrations less than 0.4 wt.%.
Impulse excitation internal friction study of dislocation and point defect interactions in ultra-low carbon bake-hardenable steel.
Authors:
Jung, I. C., Kang, D. G., & De Cooman, B. C. (2014). Metallurgical and Materials Transactions A, 45(4), 1962-1978.
Abstract:
The simultaneous presence of interstitial solutes and dislocations in an ultra-low carbon bake-hardenable steel gives rise to two characteristic peaks in the internal friction (IF) spectrum: the dislocation-enhanced Snoek peak and the Snoek-Kê-Köster peak. These IF peaks were used to study the dislocation structure developed by the pre-straining and the static strain aging effect of C during the bake-hardening process. A Ti-stabilized interstitial-free steel was used to ascertain the absence of a γ-peak in the IF spectrum of the deformed ultra-low carbon steel. The analysis of the IF data shows clearly that the bake-hardening effect in ultra-low carbon steel is entirely due to atmosphere formation, with the dislocation segment length being the main parameter affecting the IF peak amplitude. Recovery annealing experiments showed that the rearrangement of the dislocation structure lead to the elimination of the C atmosphere.
Effects of ceramic particles and composition on elastic modulus of low density steels for automotive applications.
Authors:
Rana, R., & Liu, C. (2014). Canadian Metallurgical Quarterly, 53(3), 300-316.
Abstract:
The present work deals with the effects of TiB2 ceramic particles and selected alloying elements (Al and Mn) on the elasticmodulus of steels. Steels and its composite containing varying amounts of Al, Mn and C, and a fixed amount of TiB2 particles (7.8 wt-% i.e. 13 vol.-%) were made using the bulk route of liquid steel metallurgy. All the materials were processed thermomechanically to sheet form following standard processing routes for automotive sheets. The steels containing only Al exhibited ferritic microstructures whereas addition of Mn and C caused the evolution of ferrite or austenite based duplex microstructures in the material depending on the Mn and C content. On the contrary, large TiB2 particles formed mainly by eutectic reaction from the liquid state were distributed in the ferritic matrix of the composite. All the investigated materials showed a large density drop in the range of 7.4-12.7%. Al caused a drastic drop in elastic modulus of ferritic steels whereas the elastic modulus was recovered in ferrite based duplex steel by virtue of Mn.On the contrary,Mn did not improve the elastic modulus in austenite based duplex steel. TiB2 and small amount of TiC particles in the composite were found to increase the elastic modulus by y19% in as cast condition. However, the elastic modulus of composite showed a dependence on the processing steps with decreases after subsequent hot and cold rolling steps. It was due to the delamination of particle/matrix interface, void formation and fragmentation of reinforcing particles with reduction in thickness of sheet. The elastic modulus of the composite also showed directionality due to specific alignment and various shape of ceramic particles. It was predicted that the performance and weight saving of these materials for automotive applications would be enhanced with a good combination of high strength, low density and high elastic modulus.
Thermo-mechanical sheet metal forming of aero engine components in Ti-6Al-4V–PART 1: Material characterisation.
Authors::
Odenberger, E. L., Hertzman, J., Thilderkvist, P., Merklein, M., Kuppert, A., Stöhr, T., … & Oldenburg, M. (2013). International journal of material forming, 6(3), 391-402.
Abstract:
Ti-6Al-4V is one of the most frequently used titanium alloy in aerospace applications such as for load carrying engine structures, due to their high strength to weight ratio in combination with favourable creep resistance at moderate operating temperatures. In the virtual development process of designing suitable thermo-mechanical forming processes for titanium sheet metal components in aero engine applications numerical finite element (FE) simulations are desirable to perform. The benefit is related to the ability of securing forming concepts with respect to shape deviation, thinning and strain localisation. The reliability of the numerical simulations depends on both models and methods used as well as on the accuracy and applicability of the material input data. The material model and related property data need to be consistent with the conditions of the material in the studied thermo-mechanical forming process. In the present work a set of material tests are performed on Ti-6Al-4V at temperatures ranging from room temperature up to 560°C. The purpose is to study the mechanical properties of the specific batch of alloy but foremost to identify necessary material model requirements and generate experimental reference data for model calibration in order to perform FE-analyses of sheet metal forming at elevated temperatures in Ti-6Al-4V.
The effects of Si on the mechanical twinning and strain hardening of Fe–18Mn–0.6 C twinning-induced plasticity steel.
Authors:
Jeong, K., Jin, J. E., Jung, Y. S., Kang, S., & Lee, Y. K. (2013). Acta Materialia, 61(9), 3399-3410.
Abstract:
The stacking-fault energy (SFE), dislocation slip, mechanical twinning, strain hardening, and yield and tensile strengths were systemically investigated in Fe–18Mn–0.6C–1.5Si twinning-induced plasticity (TWIP) steel. The results were also compared with those for Fe–18Mn–0.6C and Fe–18Mn–0.6C–1.5Al TWIP steels. The SFE decreased by 4 mJ m−2 per 1 wt.% Si. The addition of Si increased both the yield strength, due mainly to solid solution hardening, and the tensile strength, owing to the high strain hardening that occurred while maintaining a large elongation of over 60%. To examine this high strain hardening, especially at low strains, the volume fractions of the primary and secondary mechanical twins were quantitatively evaluated by combining the merits of electron backscattered diffractometry and transmission electron microscopy. The volume fractions of both the primary and secondary twins were the highest in the Fe–18Mn–0.6C–1.5Si TWIP steel, which had the lowest SFE of the three TWIP steels. In particular, the volume fraction of the secondary mechanical twins increased rapidly with the addition of Si. The contributions of dislocation storage, mechanical twinning and dynamic strain aging (DSA) to the strain hardening were also quantitatively evaluated in the three TWIP steels. The Si-added TWIP steel had the highest strain hardening, due mainly to the active primary and secondary twinning, and experienced negligible DSA. In contrast, the Al-added TWIP steel exhibited the lowest strain hardening due to the reductions in both the mechanical twinning and DSA.
Characterization and modeling of the elastic behavior of a XC68 grade steel used at high strain rates and high temperatures. In Key Engineering Materials (Vol. 554, pp. 1116-1124).
Authors:

Tabourot, L., Balland, P., Vautrot, M., Hopperstad, O. S., Raujol-Veillé, J., & Toussaint, F. (2013). Trans Tech Publications.

Abstract:

This article discusses the characterization and modeling of the elastic behavior of a semi-hard steel used in incremental forming operations which implies great loading speeds at high temperatures and large springback after each passage of the roller. The knowledge of the elastic behavior is essential to correctly predict these springbacks during forming. The objective is therefore on the one hand the characterization of the elastic response of the material under different conditions and on the other hand the definition of a model that describes the material behavior with as much precision as possible. To this end, two models, one phenomenological and the other built on more physical basis, are considered.

Low-density low-carbon Fe–Al ferritic steels.
Authors:
Rana, R., Liu, C., & Ray, R. K. (2013). Scripta Materialia, 68(6), 354-359.
Abstract:
Fe–Al solid-solution alloys, with interstitial-free matrix to avoid detrimental κ-carbides, have been investigated in the context of low-density steels for automotive applications. The mechanical properties of the 6.8 wt.% Al-containing alloy were found to be comparable to those of dual-phase steel but with the benefit of reduced density and better formability. Future work on these alloys should concentrate on improving the Young’s modulus and the deep drawability.
High Temperature Thermal Expansion and Elastic Modulus of Steels Used in Mill Rolls.
Authors:
Laptev, A., Baufeld, B., Swarnakar, A. K., Zakharchuk, S., & Van der Biest, O. (2012). Journal of materials engineering and performance, 21(2), 271-279.
Abstract:
The high temperature thermal expansion coefficient (TEC) and elastic modulus of five steels used in mill rolls production were investigated by dilatometer and impulse excitation techniques (IET). The measurements were provided at heating from room temperature till temperatures of about 1000°C and subsequent cooling. The obtained data were attributed to the properties of predominating phases (austenite, martensite, pearlite, and bainite). The TEC and elastic modulus of corresponding phases were similar for all investigated steels despite the difference in their chemical composition. The steels with a chromium content of 2.95wt.% and more show enhanced ability to quench hardening. This is an important prerequisite for production of high quality mill rolls. Keywordselastic modulus–microstructure–mill rolls–thermal expansion
Étude du comportement mécanique des matériaux dans des conditions étendues de vitesses et de températures: application à l'acier C68 dans le cas d'une opération de formage incrémental (Doctoral dissertation, Université Grenoble Alpes).
Author:
Vautrot, M. (2012).
Abstract:
The aim of this thesis is to characterise and model the thermo-mechanical behaviour of a high behaviour of a high-carbon steel under loading conditions identical to those of an incremental forming process at 720°C. The renewed interest in this type of process interest in this type of process stems from the fact that it is less energy-intensive and offers an attractive ratio of ratio of recycled material to raw material, resulting in improved mechanical properties for the part. The use of digital tools is now becoming an attractive solution for optimise process development. Its application requires, among other things a detailed description of the material’s behaviour under the conditions in which it is subjected to stress, i.e. over a wide range of deformation speeds and temperatures. To achieve this, it is necessary to characterisation of the material under these conditions. The mechanical behaviour of a high-carbon steel was studied using quasi-static and dynamic tensile tests to determine the dynamic tensile tests to determine the material’s sensitivity to temperature and strain rate. This characterisation is based on the innovative combination of an induction heating system controlled induction heating system and a digital image acquisition system. This The latter is used to determine deformations from displacement fields obtained by image correlation. In particular, the effects of temperature on modulus of elasticity, anisotropy and isotropic strain hardening were studied. anisotropy and isotropic strain hardening. The results of these tests then constituted an experimental database for the identification of the parameters of various models of thermo-elasto-visco-plastic behaviour. These models are more or less depending on the number of parameters used to describe the behaviour of the material over the entire range studied. This makes it possible to identify the model with the best ratio of quality/cost/time ratio for a given application. Each of the models studied therefore has its own definition domain.
Tool development based on modelling and simulation of hot sheet metal forming of Ti–6Al–4V titanium alloy.
Authors:
Odenberger, E. L., Oldenburg, M., Thilderkvist, P., Stoehr, T., Lechler, J., & Merklein, M. (2011). Journal of Materials Processing Technology, 211(8), 1324-1335.
Abstract:
In the aero engine industry alternative manufacturing processes for load carrying aero engine structures imply fabrication. The concept of fabrication involves simple forgings, sheet metals and small ingots of e.g. titanium alloys which are welded together and heat treated. In the concept phase of the product development process, accurate evaluations of candidate manufacturing processes with short lead times are crucial. In the design of sheet metal forming processes, the manual die try out of deep drawing tools is traditionally a time consuming, expensive and inexact process. The present work investigates the possibility to design hot forming tools, with acceptable accuracy at short lead times and with minimal need for the costly die try out, using finite element (FE) analyses of hot sheet metal forming in the titanium alloy Ti–6Al–4V. A rather straightforward and inexpensive approach of material modelling and methods for material characterisation are chosen, suitable for early evaluations in the concept phase. Numerical predictions of punch force, draw-in and shape deviation are compared with data from separate forming experiments performed at moderately elevated temperatures. The computed responses show promising agreement with experimental measurements and the predicted shape deviation is within the sheet thickness when applying an anisotropic yield criterion. Solutions for the hot forming tool concept regarding heating and regulation, insulation, blank holding and tool material selection are evaluated within the present work.
Young’s modulus and damping in dependence on temperature of Ti–6Al–4V components fabricated by shaped metal deposition.
Authors:
Swarnakar, A. K., Van der Biest, O., & Baufeld, B. (2011). Journal of materials science, 46(11), 3802-3811.
Abstract:
Young’s modulus and damping behavior is investigated by the impulse excitation technique in vacuum up to 1100°C for Ti–6Al–4V components, fabricated by shaped metal deposition (SMD). This is a novel additive manufacturing technique where near net-shape components are built layer by layer by tungsten inert gas welding. The Young’s modulus decreases linearly from 118GPa at room temperature to 72GPa at 900°C, followed by a stronger decrease up to 1000°C and during the first heating a plateau thereafter. The damping exhibits an exponential increase with temperature superimposed by two peaks around 700 and 900°C during the first heating. During cooling and follow-up cycles only the damping peak around 700°C appears. The change in Young’s modulus and the damping behavior is interpreted by different processes like α/β transformation, O alloying and grain boundary sliding. These results indicate that components fabricated by SMD contain a non-equilibrium α phase which transforms to the β phase at higher temperatures than the equilibrium α phase. Furthermore, the vacuum between 2.4 and 5.3×10−4mbar proved at high temperatures to be not good enough to rule out the contamination by O, which leads to α casing, stiffening, and hardening.
Characterization of Ti–6Al–4V open cellular foams fabricated by additive manufacturing using electron beam melting.
Authors:
Murr, L. E., Gaytan, S. M., Medina, F., Martinez, E., Martinez, J. L., Hernandez, D. H., … & Wicker, R. B. (2010). Materials Science and Engineering: A, 527(7), 1861-1868.
Abstract:
Ti–6Al–4V open cellular foams were fabricated by additive manufacturing using electron beam melting (EBM). Foam models were developed from CT-scans of aluminum open cellular foams and embedded in CAD for EBM. These foams were fabricated with solid cell structures as well as hollow cell structures and exhibit tailorable stiffness and strength. The strength in proportion to the measured microindentation hardness is as much as 40% higher for hollow cell (wall) structures in contrast to solid, fully dense EBM fabricated components. Plots of relative stiffness versus relative density were in good agreement with the Gibson–Ashby model for open cellular foam materials. Stiffness or Young’s modulus values measured using a resonant frequency-damping analysis technique were found to vary inversely with porosity especially for solid cell wall, open cellular structure foams. These foams exhibit the potential for novel biomedical, aeronautics, and automotive applications.