Microstructure of gas atomised γ-TiAl based alloy powders

Abstract

Due to the rapid development of advanced additive manufacturing production routes in recent years, the demand of high-quality alloy powders is significantly increased. We studied gas-atomised spherical powders of several Nb-beanng γ-TiAl based alloys, Ti-45Al-10Nb and Ti-45Al-5Nb-xC in at.% (x = 0, 0.5, 0.75, and 1), which were produced using the plasma melting induction guided gas atomization (PIGA) technique. The phase constitution of different powder fractions was determined by synchrotron high-energy X-ray diffraction at the HEMS beamline DESY (Germany), as well as by SEM, EDX and EBSD measurements. Due to the high cooling rates in the range of 10⁵ K/s, the powder particles mainly consist of hexagonal close packed α-Ti(Al) and body centred cubic β-Ti(Al)-phase. As the cooling rate depends on the particle size, considerable amounts of the β-phase were only found in the small powder fractions (< 45 µm). The total β-phase amount was generally higher in the alloy with a higher Nb content, and also the effect of carbon as a α₂-stabilizer was observed. Dendritic cauliflower-like structures are more pronounced in bigger powder particles due to the slower solidification and thus a higher Nb depletion in the remaining melt.