Effect of microstructure variations on the formation of deformation-induced martensite and associated tensile properties in a beta 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 wer e produced, with given volume fractions of beta phase (100 or 90 pet). Thes e microstructures differed in the size of their beta grains as well as in t he distribution, shape, and size of the primary alpha particles. A statisti cal approach was also developed to characterize small variations in chemist ry of the beta phase between the various microstructures. It is shown that, even for similar volume fractions of beta phase, changes in the microstruc ture strongly affect the mechanical response of the alloy. The mechanical r esponse is controlled by the interplay between the two deformation modes op erating in this alloy: formation of alpha" deformation-induced martensite a nd activation of slip, The easier formation of stress-induced martensite le ads to lower apparent yield stresses and a better work-hardening response. On the contrary, very limited work hardening is obtained when slip is activ ated solely. The differences in the ability of the martensitic transformati on to occur can be understood by considering the effect on M-s and T-0 of b oth the chemistry of the beta phase and of constraining effects due to grai n sizes and dislocations.