Microstructure and martensitic transformation in quaternary NiTiHfV alloy

The effect of age hardening on the microstructure, martensitic transformation behavior, and shape memory properties of the (Ni 50 Ti 30 Hf 20 ) 95 V 5 alloy was investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, microhardness, and bending tests. The results demonstrate a significant influence of V addition on the microstructure of the alloy. V addition leads to the formation of a (Ni,V) 2 (Ti,Hf)-type Laves phase, which coexists with B 19 ‘ martensite at room temperature. Aging at 550 °C results in precipitation hardening due to the formation of nano-scale orthorhombic H -phase, with the peak hardness observed after 3 h of aging. The alloy at peak hardness state exhibits higher transformation strain and lower unrecovered strain compared to the solution-treated sample. The aged sample achieves a maximum transformation strain of 1.56% under 500 MPa.