High-temperature tensile properties of a NiTi–Al-based alloy prepared by directional solidification and homogenizing treatment

To develop a new type of light-weight, high strength, high-temperature structural material, cast bars of a NiTi–Al-based alloy with low Nb and Hf contents were prepared by DS (directional solidification). The cast bars prepared by optimal DS were homogenizing treatment at 950 °C for different times. The tensile strength of the homogenized test samples at elevated temperatures was tested. The results reveal that the DS microstructure is a cellular–dendrite or acicular cellular structure that preferentially grows along the [0 0 1] orientation. With an increase in the drawing velocity, the cellular crystals and cellular arm spacing gradually decrease, but the directionality of the structure weakens. With an increase in the homogenization time, the cellular structure becomes increasingly coarse, and the precipitated phases are more dispersed and distributed more homogeneously. At 800 °C and 850 °C, the highest tensile strengths occur with 12 h of homogenizing treatment, resulting in strengths of up to 340 MPa and 263.6 MPa, respectively; at 900 °C, the tensile strength is 171.5 MPa. This alloy is expected to become a high-temperature structural material for applications at above 800 °C. The highest elongation at 800 °C is 42.4%, and at 850 °C and 900 °C, the highest elongation is 47.2% and 70.8%, respectively. The alloy exhibits good plasticity at high temperatures.

► The microstructure of NiTi–Al based alloy that was prepared by DS. ► At 800 °C and 850 °C, The tensile strengths are up to 340 and 263 MPa, respectively. ► The alloy exhibits excellent plasticity at high temperature.