The crystallographic features of tau(3) phase in a powder metallurgy nickel-doped Ti-45Al-5Nb-0.2C-0.2B-1.25Ni alloy

Nickel (Ni) improves the room temperature ductility, hot workability and sinterability of γ-TiAl based alloys. This study investigates the microstructure of a powder metallurgy nickel-doped Ti-45Al-5Nb-0.2C-0.2B-1.25Ni alloy based on detailed transmission electron microscopy (TEM) studies. The alloy was sintered at 1375 °C for 120 min, followed by cooling to 900 °C for a subsequent ageing treatment of 360 min. Micrometric τ3-Al3NiTi2 particles formed as a result of the solidification of a Ni-containing sintering liquid during subsequent cooling. Ageing of the as-sintered Ti-45Al-5Nb-0.2C-0.2B-1.25Ni alloy at 900 °C resulted in the precipitation of both plate-shaped and lath-shaped nanometric τ3 phase in the α2 lamellae. The constrained coincidence site lattice (CCSL) theory was used to understand the morphology and crystallography of the nanoscale τ3-Al3NiTi2 precipitates. The compression yield strength of the Ti-45Al-5Nb-0.2C-0.2B-1.25Ni alloy increased from 750 ± 20 MPa to 850 ± 20 MPa after ageing.