Effect of Inhomogeneous Oxygen Distribution on Martensitic Transformation of β Phase in Ti-15at%Nb-1at%O Alloy

The quenched-in microstructures of Ti-15at%Nb-1at%O alloy after solid solution treatment (SST) in β phase for different SST times were investigated. In the as-rolled sample before SST, the α phase formed at the grain boundaries, and coarse martensite laths of α" phase formed in the grains. In the sample after SST for the time from 0.3 to 2.4 ks, a bundle-microstructure containing α" phase laths nucleating in the same crystallographical direction was formed. In the sample with SST for 4.8ks, the α" phase laths did not form in the area at a certain distance away from the grain boundaries, and the β+ω phase formed in that area. The rest of the areas were covered by the acicular laths of α" phase. The sample after SST for 10.8 ks exhibited the acicular laths of α" phase formed uniformly in the grains. The inhomogeneous oxygen distribution would significantly affect the microstructure formation of an oxygen-containing Ti-Nb alloy.