Dependence of microstructure and mechanical properties of 60NiTi alloy on aging conditions

The microstructure evolution, hardness, compressive and tensile properties of 60NiTi alloy closely related to aging temperature and aging time are systematically characterized. Different phase compositions are achieved through aging in the temperature range of 400 °C–1000 °C for various times. The experimental results show that the variation in ductility and strength strongly depends on the microstructure. In tensile tests, a high volume fraction Ni4Ti3 phase precipitated after aging at 400 °C, 500 °C and 900 °C, resulting in high tensile strength and low elongation. The 60NiTi alloy fractured in brittle mode. The precipitations of the alloys which aged at 600 °C for 12 h and 700 °C for 3 h, 6 h, and 12 h are Ni3Ti2 and Ni3Ti phases. Alloys with Ni3Ti2 and Ni3Ti showed plastic deformation during tensile testing. The fracture surface morphology after tensile testing was characterized by SEM, and the microstructure of the samples after deformation was analyzed with TEM. It was found that the active dislocations in the matrix cut through the Ni3Ti2 and Ni3Ti phases, which resulted in plastic deformation. The relationship between the microstructure and mechanical properties of 60NiTi alloy is discussed in the pursuit of the ideal structure.