Mechanical and thermodynamic properties of intermetallic compounds in the Ni–Ti system

Abstract

The mechanical and thermodynamic properties of intermetallic compounds in the Ni–Ti system are studied by first-principles calculations. All phases show anisotropic elasticity in different crystallographic directions, in which Ni 3 Ti and NiTi 2 are approaching the isotropy structure. The elastic moduli and Vicker’s hardness of Ni–Ti system intermetallic compounds decrease in the following order: Ni 3 Ti [Formula: see text] B2_NiTi [Formula: see text] B19[Formula: see text]_NiTi [Formula: see text] NiTi 2 , and Ni 3 Ti shows the best mechanical properties. The intrinsic ductile nature of Ni–Ti compounds is confirmed by the obtained [Formula: see text]/[Formula: see text] ratio. The temperature dependence of linear thermal expansion coefficients (LTECs) of the compounds is estimated by the quasi-harmonic approximation (QHA) method. Ni 3 Ti shows the largest values among all Ni–Ti intermetallic compounds. At room temperature, the LTEC for Ni 3 Ti is 8.92 × 10[Formula: see text] K[Formula: see text], which falls in between the LTEC of zirconia toughened alumina (ZTA) (7.0–9.5 × 10 6 K[Formula: see text]) and iron matrix (9.2–16.9 × 10 6 K[Formula: see text]); i.e., the thermal matching of the ZTA/iron composite will be improved by introducing Ni 3 Ti intermetallic compound into their interface. Other thermodynamic properties such as sound velocity and Debye temperature are also obtained.