Variant selection in metastable β Ti-V-Fe-Al alloy during triaxial and uniaxial compression

Abstract

In the present study, metastable β-Ti alloy Ti-10V-3Fe-2Al (wt%) alloy was subjected to either triaxial or uniaxial compression followed by aging of both as-deformed as well as solution-treated samples. Microstructural characterization and measurement of crystallographic texture were performed to elucidate the underlying mechanism affecting the measured hardness of these differently processed samples. The microstructure of the as-deformed material was highly inhomogeneous consisting of β grains fragmented by microbands. Aging of the solution-treated as well as deformed samples resulted in the formation of a two-phase α + β microstructure. The texture of the β phase in the triaxial compressed alloy was dominated by cube component, while in uniaxial compression it exhibited strong fiber texture. The differences in texture in the parent β matrix influenced the transformation texture of the α phase formed during aging. A strong variant selection of the α precipitates was observed in both triaxially and uniaxially deformed samples. A mechanism of variant selection is proposed wherein, the inhomogeneous deformation leads to preferential precipitation of α phase along the crystallographic microbands resulting in a variant selection. The variation in texture resulting from the difference in strain path affected the mechanical property and its anisotropy. Hardness after uniaxial compression, was anisotropic because of the texture evolved during the process, whereas, triaxially compressed material was found to have isotropic hardness properties. Aging led to a reduction in anisotropy as the effect of precipitation dominated over the orientation effect on overall strengthening. Thus, coupling strain path with aging treatment can be used to tailor the mechanical properties in a Ti-V-Fe-Al alloy.