Effect of αp/βtrans interfacial microstructure on tensile property and deformation behavior in Ti6242 alloys

Abstract

A Ti6242 alloy with a semi-equiaxed structure (S-ES) was obtained by controlling the gradient distribution of Mo between αp and βtrans. The formation, deformation behavior, and tensile properties of the S-ES in the Ti6242 alloy were investigated. The S-ES was formed via a local α→β transformation occurring only in the micro-zone adjacent to the αp/βtrans boundary (αp: primary α phase; βtrans: transformed β structure), followed by rapid cooling and aging. A transition zone was formed to replace the original αp/βtrans interface boundary, effectively improving the stress concentration at the boundary in the equiaxed microstructure. Such a transition zone consists of gradient nanoprecipitations (β phase) with a decreased density and size in the direction of αp. The β precipitates in the transition zone formed by the S-ES were coherent with the α matrix and strengthened the αp matrix. This was evidenced by in situ observations of deformation being shared by βtrans and αp for S-ES and cracks preferentially nucleating in βtrans instead of at the transition zone (original αp/βtrans interface). The αs/βr interfaces (αs: secondary α; βr: residual β phase) in βtrans, which are almost perpendicular to the tensile direction, became the main sites of crack initiation in S-ES. Furthermore, the yield strength of S-ES increased to 1247 MP owing to the precipitation-strengthening effect of βr in the transition zone. In principle, the S-ES design approach applies to other dual-phase titanium alloys.