Impact Response and Microstructural Evolution of Biomedical Titanium Alloy under Various Temperatures

Abstract

A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behavior and microstructural evolution of biomedical Ti alloy deformed at strain rates ranging from 8 · 10 2 s -1 to 8 · 10 3 s -1 at temperatures between 25°C and 900°C. In general, the results indicate that the mechanical behavior and microstructural evolution of the alloy are highly sensitive to both the strain rate and the temperature conditions. The flow-stress curves are found to include both a work-hardening region and a work-softening region. The strain-rate-sensitivity parameter, b, increases with increasing strain and strain rate but decreases with increasing temperature. The activation energy varies inversely with the flow stress and has a low value at high deformation strain rates and low temperatures. Microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result primarily of dislocations and the formation of a phase. The dislocation density increases with increasing strain rate but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. Correlating the mechanical properties of the biomedical Ti alloy with the TEM observations, it is inferred that the precipitation of a phase dominates the fracture strain. Transmission electron microscope observations reveal that the amount of a phase increases with increasing temperature below the b-transus temperature. The maximum amount of a phase is formed at a temperature of 700°C and results in the minimum fracture strain observed under the current loading conditions.

The dynamic response of a β titanium alloy to high strain rates and elevated temperatures

“…In equation (5), stresses ı 1 and ı 2 are obtained from tests conducted at temperatures of ଵ and ଶ , respectively. For Ti6554, the strain rate sensitivity decreases with increasing temperature as shown in Fig.4a, which is also observed for most other metals [20,21,[32][33][34]. The temperature sensitivity of Ti6554 increases with increasing temperature.…”

“…This indicates that shear bands tend to form at higher strain rates. It has been reported that high strain rates and low temperatures are beneficial for the formation of shear bands in titanium alloys [20]. However, in this study it was observed that the adiabatic shear bands prefer to form at higher temperatures.…”

“…In addition, a strain rate softening behaviour was observed for a kind of high manganese steel in the range of ~500-1700 s -1 [15]. Khan et al [16], Nemat-Nasser et al [17], Hokka et al [18] and Lee et al [19][20][21] have done similar dynamic experiments on titanium alloys and observed that the flow stress is sensitive to high strain rates and elevated temperatures. For the Ti6Al4V [19] and Ti15Mo5Zr3Al [21] alloys, it was observed that the flow stress is more sensitive to temperature than strain rate.…”

The dynamic response of β titanium alloys to high strain rates at room and elevated temperatures

“…As to temperature sensitivity, there exist some contradictions. In Refs [85,118,121,129], the temperature sensitivity of the investigated metals was interpreted to increase with increasing strain, strain rate and…”

“…As to temperature sensitivity, there exist some contradictions. In Refs [85,118,121,129], the temperature sensitivity of the investigated metals was interpreted to increase with increasing strain, strain rate andHongyi Zhan have conducted dynamic compressive tests on the β Ti-Nb-Zr-Mo-Sn alloy and found that the flow stress decreased slightly when the strain rate was raised to 1000 s -1 as shown in Fig.14. It may be attributed to the fact that high strain rates increased the volume fraction of α" martensitic phase which has a lower hardness than β phase.…”