Uncovering the fracture mechanism of Laves (1 1 1)/ Ni6Nb7 (0 0 0 1) interfaces by first-principles calculations

Engineering materials interface is key in determining the comprehensive service performance of different structures owing to its complex structure and interfacial chemical characteristics. In this work, we investigate the energetic properties and fracture mechanism of Laves (1 1 1)/ Ni ₆Nb ₇ (0 0 0 1) interfaces in electron beam welded Nb/GH3128 dissimilar joint interface using first principles calculations combined with high-resolution transmission electron microscope (HRTEM) experiments. 48 interface models are constructed considering both surface terminations and atomic configurations of interfaces. It is found that interface atomic structure change occurs in many interfaces. i.e. interface rearrangement. Compared to interfacial atomic configuration, surface termination has a greater impact on interface stability. The computational work of adhesion and interfacial energy indicate that all interfaces can stably exist and interface rearrangement is beneficial for improving the bonding strength of interfaces. Ni-Nb bonds at Laves (1 1 1)/ Ni ₆Nb ₇ (0 0 0 1) interfaces are proven to play the dominant role in weakening the interfacial cohesion. The effect of chemical bonds on the cohesion of interfaces is further quantified by integrating crystal orbital Hamilton populations (ICOHP). It turns out that in-plane chemical bonds are detrimental to interfacial bonding. On the contrary, cross-interface bonds can help prevent interface fracture. A close relationship is found between atomic bond type and bonding strength: Nb-Nb bonds possess similar strength as Nb-Cr bonds but significantly higher than Nb-Ni bonds.