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NiTi–Al-based alloys are promising high-temperature structural materials for aerospace and astronautics applications.A new NiTi–Al-based alloy Ni–43Ti–4Al–2Nb–2Hf(at%)was processed via isothermal forging.The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope(SEM),X-ray diffraction(XRD),and tensile tests.Results show that the microstructure of as-forged Ni–43Ti–4Al–2Nb–2Hf alloy consists of NiTi matrix,Ti2Ni phase,and Hf-rich phase.The simultaneous addition of Nb and Hf,which have strong affinities for Ti sites,promotes the precipitation of Hf-rich phases along the grain boundaries.The tensile strengths of Ni–43Ti–4Al–2Nb–2Hf alloy are dramatically increased compared with the ternary Ni–46Ti–4Al alloy.At room temperature and 650°C,the yield stress of Ni–43Ti–4Al–2Nb–2Hf alloy reaches 1,070 and 610 MPa,respectively,which are 30%and 150%higher than those of Ni–46Ti–4Al alloy.The improved tensile property results from the solid solution strengthening by Nb and Hf,as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.
NiTi-Al-based alloys are promising high-temperature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni-43Ti-4Al-2Nb-2Hf (at%) was processed via isothermal forging. properties at room temperature and high temperature were investigated through scanning electron microscope (SEM), X-ray diffraction (XRD), and tensile tests. Results show that the microstructure of as-forged Ni-43Ti-4Al-2Nb-2Hf alloy consists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. Tensile strength of Ni-43Ti-4Al -2Nb-2Hf alloy are dramatically increased compared to the ternary Ni-46Ti-4Al alloy. At room temperature and 650 ° C, the yield stress of Ni-43Ti-4Al-2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, respectively are 30% and 150% higher than those of Ni-4 6Ti-4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.