Formation characteristics of Ni/Ti intermetallics through annealing of layered Ni/Ti

Ni/Ti diffusion couples were prepared by cold spraying with Ni and Ti powders and mechanically alloyed Ni/Ti alloy powders.The formation and growth characteristics of Ni/Ti intermetallics within Ni/Ti during solid state diffusion treatment were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD).It was found that the thicknesses of Ni₃Ti,NiTi and Ti₂Ni intermetallic compounds layers increased with annealing temperature.The growth of TiNi layer followed the parabolic law with annealing time while the thicknesses of Ti₂Ni or Ni₃Ti layers were kept constant at certain annealing temperature.The results suggest that the formation and then rapid growth of TiNi intermetallic take place after Ni₃Ti and Ti₂Ni intermetallic compounds grow to certain thicknesses.