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.