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

A Ti6242 alloy with a semi-equiaxed structure (S-ES) was obtained by controlling the gradient distribution of Mo between alpha(p) and beta(trans). 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 alpha ->beta transformation occurring only in the micro-zone adjacent to the alpha(p)/beta(trans) boundary (alpha(p): primary alpha phase; beta(trans): transformed beta structure), followed by rapid cooling and aging. A transition zone was formed to replace the original alpha(p)/beta(trans) interface boundary, effectively improving the stress concentration at the boundary in the equiaxed microstructure. Such a transition zone consists of gradient nanoprecipitations (beta phase) with a decreased density and size in the direction of alpha(p). The beta precipitates in the transition zone formed by the S-ES were coherent with the alpha matrix and strengthened the alpha(p) matrix. This was evidenced by in situ observations of deformation being shared by beta(trans) and alpha(p) for S-ES and cracks preferentially nucleating in beta(trans) instead of at the transition zone (original alpha(p)/beta(trans) interface). The alpha(s)/beta(r) interfaces (alpha(s): secondary alpha; beta(r): residual beta phase) in beta(trans), 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 beta(r) in the transition zone. In principle, the S-ES design approach applies to other dual-phase titanium alloys.

Automated summary

A semi-equiaxed structure (S-ES) was obtained in a Ti6242 alloy by controlling the distribution of Mo between different phases. The S-ES was formed through a localized phase transformation and rapid cooling. The formation of a transition zone improved stress distribution at the interface and the presence of precipitation strengthened the matrix. This design approach is applicable to other dual-phase titanium alloys.