Atomic-scale interfacial strengthening mechanism of nano intermetallic compounds in Ti-Ni bimetallic alloys

Abstract

It is well established that cracking induced by Ti-Ni intermetallic compounds (IMCs) severely compromises the application of Ti-Ni bimetallic alloys in extreme environments. However, recent research has demonstrated that reducing the size of these originally detrimental IMCs from the micrometer to the nanometer scale can enhance the plasticity and strength of the metal. To investigate the effects of nanoscale IMCs on the deformation mechanisms of Ti-Ni bimetallic alloys under high strain, we employed molecular dynamics (MD) simulations to study the mechanical deformation mechanisms of two common IMCs at the interface of Ti-Ni bimetallic alloys, namely Ti₂Ni and TiNi₃, and their influence on the interfacial bonding strength of the alloy. Both lamellar and particulate configurations were considered.The results of uniaxial tensile tests reveal that Ti₂Ni undergoes atomic-scale rearrangement after yielding, exhibiting high ductility but low strength. In contrast, TiNi₃ is highly brittle and exhibits limited slip. In the context of Ti-Ni bimetallic alloys, the interface between lamellar Ti₂Ni and the Ti layer is highly susceptible to stress concentration due to the lack of long-range order in the Ti₂Ni structure. The semi-coherent interface between lamellar TiNi₃ and the Ti layer is the primary cause of brittleness at the Ti-Ni interface. Additionally, the presence of particulate IMCs acts as dislocation sources, activating slip in the Ni layer, thereby enhancing overall plasticity at the expense of some strength.Our simulation work provides a potential approach for designing high-performance Ti-Ni bimetallic alloys and elucidates the deformation mechanisms of Ti₂Ni and TiNi₃ within the alloy matrix.