Young's modulus and mechanical properties of Ti-29Nb-13Ta-4.6Zr in relation to α" martensite

An investigation on the formation of alpha" martensite and its influence on Young's modulus and C mechanical properties of forged Ti-29Nb-13Ta-4.6Zr (wt pet) alloy is reported in this article. For ice-water-quenched specimens after solution treatment at 1023, 1123, and 1223 K in the single beta-phase field for 1.8, 3.6, 14.4, and 28.8 ks, X-ray diffraction and internal friction measurements showed that the volume fraction of the a" martensite changes with both solution temperature and time. This effect has been attributed mainly to the influence of grain size of the beta-parent phase on the stability of the beta phase and, consequently, on the martensitic start (Ms) temperature. A critical grain size of 40 mum was identified for the beta phase, below which the martensitic transformation is largely suppressed because of low Ms temperature. With the beta grain size increasing above this critical value, the volume fraction of the alpha" martensite increases significantly at first and then decreases gradually with further grain growth. The alpha" martensite was shown to possess good ductility and, compared to the beta phase, lower strength and hardness but nearly identical Young's modulus in the studied alloy.