Effect of microstructure variations on the formation of deformation-induced martensite and associated tensile properties in a β metastable Ti alloy

This article focuses on the effect of the microstructure on the activity of different deformation mechanisms and the resulting mechanical behavior of a metastable beta Ti alloy (beta-Cez). Various types of microstructures were produced, with given volume fractions of beta phase (100 or 90 pet). These microstructures differed in the size of their beta grains as well as in the distribution, shape, and size of the primary alpha particles. A statistical approach was also developed to characterize small variations in chemistry of the beta phase between the various microstructures. It is shown that, even for similar volume fractions of beta phase, changes in the microstructure strongly affect the mechanical response of the alloy. The mechanical response is controlled by the interplay between the two deformation modes operating in this alloy: formation of alpha" deformation-induced martensite and activation of slip, The easier formation of stress-induced martensite leads to lower apparent yield stresses and a better work-hardening response. On the contrary, very limited work hardening is obtained when slip is activated solely. The differences in the ability of the martensitic transformation to occur can be understood by considering the effect on M-s and T-0 of both the chemistry of the beta phase and of constraining effects due to grain sizes and dislocations.