First-principles calculation on the adhesion strength, fracture mechanism, interfacial bonding of the NiTi (111)//α-Al₂O₃ (0001) interfaces

NiTi//Al₂O₃ composites have many advantages such as large elasticity, superior hardness and wear resistance. But there is little information available about the novel adhesion strength, fracture mechanism and interfacial bonding of NiTi//Al₂O₃ composites at the atomic scale. Therefore, the work of adhesion (W_ad), interfacial energy (γ) and electronic structure of NiTi(111)//α-Al₂O₃(0001) interfaces have been calculated using first-principles calculations. For the models with the same stacking site, O-terminated interfaces have larger W_ad and smaller γ than Al-terminated interfaces. For the models with same termination, the stability of Ni(Ti)-Al interfaces decreases with the order of HCP > MT > OT, while the stability of Ni(Ti)-O interfaces decreases as MT > HCP > OT. The Ti-O-MT interface belongs to the most stable interfacial configuration with the smallest interface energy among all studied interfaces. Using Griffith's theory, it is predicted that the mechanical failure of NiTi//α-Al₂O₃ interfaces are inclined to initiate in the interior of NiTi bulk or at the interface rather than Al₂O₃ side in most cases. Furthermore, density of states and electron density difference analysis indicate that the dominant interfacial adhesion mechanism for the Ni–Al interfaces is the formation of mainly metallic Ti–Al and Ni–Al bonds, while the Ti–O interface exhibits mixed covalent/ionic character with higher interfacial binding strength.