Interfacial study of NiTi–Ti₃SiC₂ solid state diffusion bonded joints

The interfaces between the stress-assisted diffusion bonded Ti₃SiC₂ and equiatomic NiTi, two distinct material systems that show pseudoelasticity were studied. The interfaces were formed in the 800–1000 °C temperature range, for 1, 5 and 10 h under flowing argon. Bonding was observed in all the cases considered, except at 800 °C after 1 h. Morphology and reaction phases in the interface were characterized using scanning electron microscopy, elemental micro probe analysis and electron backscatter diffraction analysis. The interfacial structure formed between NiTi and Ti₃SiC₂ layers consists of NiTi/Ti₂Ni/Ti₅Si₃/NiTiSi/Ti₃SiC₂. Diffusion of Si into NiTi from Ti₃SiC₂, and Ni from NiTi into reaction zone was found to be responsible for the formation of reaction layers in the interface and thus for bonding at these conditions. The overall reaction layer thickness grows following the parabolic kinetic law. Nano-indentation and Vickers micro hardness tests were carried out to investigate the mechanical properties of the interface. Nano-indentation showed that the elastic moduli of the phases in the interface are close to that of Ti₃SiC₂ while their hardness is higher than that of both Ti₃SiC₂ and NiTi. Artificially formed cracks through microindents were observed to be branched and propagated into Ti₃SiC₂ phase indicating good resistance against delamination