Microstructure evolution and tensile properties of conventional cast TiAl-based alloy with trace Ni addition

The microstructure evolution and tensile properties of Ti-48Al-2Cr-2Nb-0.25Ni alloy fabricated by the induction skull melting (ISM) process were investigated. Results showed that the influence of trace Ni addition on the cast microstructure was slight, while the γ phase fraction increased relatively. After tensile tests at elevated temperature, nanoscale τ3 particles precipitated within the lamellar colony in the gauge area. The τ3 phase exhibited the specific orientation relationship with the α2 and γ phases: (224̅2)τ3//(404̅1)α2//(113)γ and [11̅00]τ3//[112̅0]α2//[1̅10]γ. At elevated temperature, the UTS and εf were enhanced evidently by Ni addition than that of Ti-48Al-2Cr-2Nb alloy. Dislocations were pinned by the nanoscale τ3 precipitates during tensile deformation at elevated temperature. The nanoscale τ3 precipitates and increased γ phase fraction induced by Ni alloying could account for the notable tensile properties in the present work. The precipitation behavior and the main strengthening mechanism were analyzed and discussed in detail.