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

In the present study, two powders near-b Ti

alloys having a nominal composition of Ti-5Al-5Mo-5VXCr-

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 C) in the b

phase field. The b ? a phase transformation occurred

during soaking at 1023 K (750 C) in the a ? b phase

field. Fragmentation of the continuous grain boundary a

occurred because of the 40 % deformation at 1023 K

(750 C). Variation in the concentration of the alloying

elements in each phase took place through the diffusion

during soaking in the a ? b phase field, e.g. exit of

b-stabilisers from the a-phase. However, the a phase

remained supersaturated with b stabilisers. Deformation

had no influence on the distribution of the alloying elements.

An addition of 1 % Cr content slightly affects the

amount of the a phase formed and b grain size, but it has no

noticeable effect on the distribution of the alloying elements

between the phases.