Shock and Microstructural Characterization of the $$\alpha$$ α – $$\omega$$ ω Phase Transition in Titanium Crystals

Abstract

A multicrystal comprised of a small number of large crystals of high-purity titanium and a $$[0001]$$ oriented high-purity single crystal titanium sample were shock loaded using gas gun plate impact experiments. Tests were performed at stresses above the $$\alpha {-}\omega$$ phase transition stress (for high-purity polycrystalline specimens) to observe the behavior of oriented crystals under similar conditions. Post-mortem characterization of the shocked microstructure was conducted on the single crystal sample to measure textures, and quantify phases and twinning. The apparent activation of plastic and transformation mechanisms was dependent upon crystal orientation. Specifically, the $$[0001]$$ crystal showed a higher Hugoniot elastic limit than the $$[10\bar{1}0]$$ or $$[3\bar{1}\bar{4}4]$$ orientations. The slope of velocity as a function of time was lower in the $$[0001]$$ orientation than the other orientations during plastic deformation, indicating sluggish transformation kinetics for the $$\alpha$$ to $$\omega$$ phase transition for the $$[0001]$$ oriented crystal. Microtexture measurements of a recovered $$[0001]$$ oriented single crystal revealed the presence of retained $$\omega$$ phase after unloading, with orientations of the constituent phase fractions indicative of the forward $$\alpha \rightarrow \omega$$ transition, rather than the reverse $$\omega \rightarrow \alpha$$ transition, suggesting that the material never achieved a state of 100% $$\omega$$ phase.