Microstructure evolution and alloying elements distribution between the phases in powder near-β titanium alloys during thermo-mechanical processing

In the present study, two powders near-beta Ti alloys having a nominal composition of Ti-5Al-5Mo-5V-XCr-1Fe (X = 1-2, wt%) were studied. The alloys were produced via the blended elemental powder metallurgy technique using hydrogenated Ti powder. Microstructure evolution and the distribution of the alloying elements between the phases were investigated after each step of thermo-mechanical processing (TMP). Microstructures were refined through the TMP in both alloys. Porosity was reduced with deformation at 1173 K (900 A degrees C) in the beta phase field. The beta A -> A I +/- phase transformation occurred during soaking at 1023 K (750 A degrees C) in the alpha A + beta phase field. Fragmentation of the continuous grain boundary alpha occurred because of the 40 % deformation at 1023 K (750 A degrees C). Variation in the concentration of the alloying elements in each phase took place through the diffusion during soaking in the alpha A + beta phase field, e.g. exit of beta-stabilisers from the alpha-phase. However, the alpha phase remained supersaturated with beta stabilisers. Deformation had no influence on the distribution of the alloying elements. An addition of 1 % Cr content slightly affects the amount of the alpha phase formed and beta grain size, but it has no noticeable effect on the distribution of the alloying elements between the phases.