Microstructure and Properties of an Equiatomic TaTiZr Alloy

Abstract Microstructure and compression mechanical properties of a ternary TaTiZr alloy, after hot isostatic pressing (HIP) at 1400 °C, are reported. In the slow cooled condition, the alloy had a coarse-grained structure consisting of Zr-rich BCC matrix and Ta-rich submicron-sized BCC precipitates, which were coherent to the matrix phase. Ti was almost equally distributed between these two phases. omega-phase nano-precipitates were also detected inside the Zr-rich matrix. According to CALPHAD analysis, the observed microstructure is a metastable one, which was formed in the temperature range of 800–1130 °C during cooling after HIP. The HIP'd alloy had high yield stress of 1671 MPa at 25 °C and 1440 MPa at 400 °C, but low ductility, likely due to the presence of the omega phase. Considerable alloy softening, accommodated by a noticeable increase in ductility, occurred between 400 °C and 600 °C, with the yield stress decreasing to 346 MPa at 600 °C, 157 MPa at 800 °C and 103 MPa at 1000 °C. Such dramatic change in the mechanical behavior was correlated with dissolution of the omega phase and approaching phase equilibrium at T ≥ 600 °C.