The alloying effect of Cu on thermal and mechanical behavior in Ni 50-x Ti 35 Zr 15 Cu x (x = 0, 3, 5, 10, 15 at.%) shape memory alloys has been systematically investigated in the present study. The addition of Cu changes the lattice parameters and expands the unit cell volume of B2 austenite and B19’ martensite. With alloying Cu, the temperature for austenite ↔ martensite transformation tends to decrease, and the transformation from B2 austenite to B19’ martensite occurs in a single step mode. The decrease of transformation temperature with alloying Cu is attributed to the chemical stabilization of B2 (destabilization B19’) which is reflected by the decrease of the transformation enthalpy. The stabilization of B2 comes along with the increase of valence electron concentration and non-basal shear modulus resisting to transformation into B19’. While, the destabilization of B19’ structure is represented by the increase of monoclinic angle. When compared to the ternary Ni 49.5 Ti 50.5-x Zr x (x = 0, 3, 5, 10, 15, 18, 20 at. %) and Ni 50-x Ti 50 Cu x (x = 0, 2.5, 5, 7.5, 10 at. %) alloys, the stabilization of B2 (destabilization B19’) is more pronounced in the Ni–Ti–Zr–Cu alloys investigated in the present study. Due to the change of thermal and structural properties with alloying Cu, the temperature dependence of stress for inducing martensitic transformation gradually decreases and the superelastic window is enlarged. As a result, the superelastic recovery is enhanced with alloying Cu.
Bibliographical noteFunding Information:
This work was supported by the Samsung Science & Technology Foundation .
© 2019 Elsevier Ltd
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry