The crystallographic features of τ3 phase in a powder metallurgy nickel-doped Ti–45Al–5Nb–0.2C–0.2B–1.25Ni alloy. (April 2016) - Xia, Y.
Abstract: 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 τ 3 -Al3 NiTi2 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 -Al3 NiTi2 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. Highlights: Micrometric τ 3 -Al3 NiTi2 phase was identified by transmission electron microscopy. Ageing of the alloy results in the formation of nanometric τ3 precipitates with two types of morphology in the α2 lamellae. The orientation relationships of two kinds of τ 3 -Al3 NiTi2 phase with α2 phase were identified. The constrained coincidence site lattice theory was used to understand the morphology and crystallography of the τ3 .