Influence of the second phase on the room-temperature tensile and creep deformation mechanisms of α-β titanium alloys:: Part I.: Tensile deformation

The effects of alpha and beta phase interactions on the room-temperature tensile and creep deformation behavior of alpha + beta titanium alloys with Widmanstatten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy systems. This article, Part I, deals with tensile deformation. It was found that when the a phase is present as thin (< 10-mu m) plates in the alpha + beta alloys, significant twinning occurs. No significant twinning was observed in single-phase alloys with the same chemistry and similar grain size. Additionally, the beta phase of Ti-8.1 V deforms by stress-induced hexagonal martensite (alpha'), while only twinning occurs in the single-phase beta alloy with the same chemistry. Twinning in the a phase in association with stress-induced martensite (SIM) in the beta phase was observed for the first time in a two-phase titanium alloy. This behavior is explained in terms of a number of factors including elastic interaction stresses between the alpha and beta phases, coherency between the a phase and hexagonal martensite, and beta phase stability.