Myung-Chul Shin

New titanium alloys for biomaterials: a study of mechanical and corrosion properties and cytotoxicity.

Three new titanium alloys with Zr, Nb, Ta, Pd and In as alloying elements were developed and compared with currently used implant metals, namely, pure Ti and Ti-6Al-4V alloy, in terms of mechanical and corrosion properties, and cytotoxicity. New alloys showed comparable mechanical properties with that of the Ti-6Al-4V alloy, but increased corrosion potential, somewhat decreased breakdown potential and increased corrosion rate. There were no significant differences in cell growth on the surface of the various metal specimens, indicating that the cells cannot differentiate between the passivated surfaces of the various Ti metals.

Damping mechanism and application of Fe-Mn based alloys

Abstract The damping mechanism and its application in Fe-Mn based high damping alloys are studied in this work. The mechanism of damping capacity is proposed by correlating it with the microstructure, which is varied through changes in grain size. The Fe-Mn based alloys are successfully applied as a part of a stone cutter, reducing the noise by 10–25 dB.

Damping capacity in Fe-Mn based alloys

Abstract 1. 1) Stacking faults and e martensite both act for damping with the latter much more effective. The damping capacity by e martensite is proposed to be caused by the phase boundary movement with the static hysteresis on vibration. 2. 2) We show that damping capacity of Fe-Mn based alloys depends on the area and mobility of Y/E boundary by varying microstructure. At a low strain amplitude, the area is more dominant than the mobility, and reverse is also true.

Effects of grain shape and texture on the yield strength anisotropy of Al-Li alloy sheet

The in-plane anisotropy of yield strength in aluminum-lithium (Al-Li) alloys has been attributed to crystallographic textures, grain morphologies, and directional precipitates. Hot-rolled Al-Li alloys are reported to exhibit the minimum yield strength near 45{degree} to the rolling direction due to rolling textures (i.e., Cu, S and Bs components in {beta}-fiber) and elongated grains. During recrystallization treatment in the thermo-mechanical processing, continuous recrystallization (CRX) or discontinuous recrystallization (DRX) can take place. It is known that CRX occurs by formation and growth of subgrains, while the DRX occurs by growth of newly developed nuclei with different crystal orientations from those of original grains. CRX hardly alters texture, on the contrary DRX completely changes the texture. The grain morphology of CRX, affected by rolling and recrystallization conditions, can be controlled without changing crystallographic textures. In this work, equiaxed grains with rolling textures are obtained by CRX, and the contributions of grain shape and texture to the in-plane anisotropy of yield strength have been identified in an Al-Li-Cu-Mg-Zr-Mn alloy.

The effect of silver addition on 7055 Al alloy

Abstract The effect of silver addition on the microstructure and mechanical properties of the 7055 Al alloy was investigated. Mechanical properties of various alloys used in this study are correlated with the formation of constituent particles and microstructural changes of fine precipitates. According to the experiment, tensile strength of the 7055 Al alloy decreased by the addition of silver, although silver additions were observed to refine η′. The low tensile strength is attributed to the relatively low number density of η′ in silver-bearing alloys in which a large amount of hardening elements, such as Zn and Mg, are consumed to form silver-bearing constituent particles.

Measurement of volume fraction of stress-induced εs martensite in Fe-32Mn-6Si alloy

Fe-Mn-Si alloy has drawn much attention due to its shape memory effect and damping capacity which are based on {gamma} {leftrightarrow} {var_epsilon} non-thermoelastic transformation. Thermoelastic martensitic alloys like Ni-Ti undergo complete transformation if they are cooled below Mf temperature. In a Fe-Mn-Si alloy, however, the volume fraction of {var_epsilon} martensite below Mf depends on its heat treatment condition because of the incomplete non-thermoelastic transformation. Thus measurement of the volume fraction of {epsilon} martensite is necessary to correlate it with some physical and mechanical properties. In this work, the authors propose a new way of measuring the volume fraction of stress-induced {epsilon} martensite based on the volume expansion accompanying {var_epsilon} {yields} {gamma} transformation. Cold rolling is applied to generate anisotropic {var_epsilon} martensite, and the length change is measured in the RD, TD and ND during heating. Dilatometric behavior in the three directions and variation in the volume fraction are investigated with various degrees of cold rolling.

The corrosion and tarnish behavior of new palladium-indium system alloys

Emphasis on reduced costs has led to the greater use of economic alloys. Previous work has designed alloys with physical and mechanical properties similar to those of high gold alloys. Evaluation for the degree of corrosion and tarnish are to followed quantitatively by potentiodynamic and spectrophotometer analysis. In the view of the development in low nobility alloys, it is important that such testing be standardized to characterize the corrosion and tarnish properties of the compositions. But there are concerns with the long term chemical stability of these alloys, the resistance to corrosion and tarnish. Chemical stability is a complex problem involving alloy composition, nobility, microstructure and environment.