Precipitation and segregation in α2+γ titanium aluminides

Precipitation and segregation of the alloying elements in α2+γ Ti–47at.% Al–2% Cr–1.8% Nb doped with 0.15 at.% B and 0.20 at.% W in both a stress-relieved and an aged condition were investigated by atom probe field ion microscopy. The boron concentrations were found to be significantly depleted below the nominal alloy content in both the α2 and γ phases in both the stress-relieved and aged alloys. The majority of the boron was in a variety of borides including TiB, TiB2 and (Ti,Cr)2B. An initial rejection of tungsten and chromium from the γ phase in the stress-relieved alloy was observed to reverse upon aging. Tungsten and chromium were also observed to segregate to both α2–γ and γ–γ interfaces. The average tungsten coverage at the lamellar interfaces in the stress-relieved alloy was determined to be 2.3% W. In the aged alloy, a chromium enhancement in the γ phase near α2–γ interfaces was observed.