Oxygen induced phase transformation in an α+β titanium alloy

Abstract

Abstract It is critical to understand oxygen (O) ingress behavior in titanium alloys at high temperatures, since it was directly associated with their high-temperature performance. Investigations revealed that the diffusion of O would result in a uniform α-case layer beneath the surfaces of titanium alloys. This layer greatly affected the mechanical performance of the alloys. In the present study, a novel O ingress phenomenon in an α+β titanium alloy was observed. After the isothermal treatment in the air, a two-layered region beneath the specimen surfaces was formed: the outer layer (layer A) uniformly grew parallel to the diffusion direction of O; while the inner layer (layer B) precipitated within the first β grain beneath layer A, arranging in specific orientations. By experimental investigation as well as theoretical analysis, the formation mechanism of the unique layers was understood: with the diffusion of O, an α+β layer (layer A) was uniformly formed beneath the specimen surfaces, while creating a new interface between layer A and the matrix. This interface acted similarly as αGB during the precipitation of αWGB (layer B). In addition, Burgers orientation relationship was strictly obeyed during the formation of layer B.