Effect of self-propagating high-temperature combustion synthesis on the deposition of NiTi coating by cold spraying using mechanical alloying Ni/Ti powder

Nickel titanium alloy powder was fabricated by mechanical alloying process. The powder was employed to form Ni50-Ti50 alloy deposit by cold spraying. The thermal stability of the as-milled powders was characterized by differential scanning calorimetry. The surface morphology and cross-sectional microstructure of the coatings were examined by scanning electron microscopy (SEM). The coating microstructure was also characterized by X-ray diffraction analysis. It was observed that the Self-propagating High-temperature combustion Synthesis (SHS) phenomenon occurs during cold spraying using Ni/Ti mechanical alloying powders. The deposition efficiency of Ni50-Ti50 coating was significantly influenced by the SHS reaction level of MA powder. The gas temperature igniting the SHS reaction during cold spraying decreased with the increase of ball milling time. The ignition of SHS reaction led to partial melting of Ni/Ti powder. It was found that the melted particle fraction which resulted from SHS reaction led to splashing of spray particles off substrate on impact, which significantly decreased the deposition efficiency. A model was proposed to explain the coating deposition behavior during cold spraying using the mechanically alloyed metastable Ni/Ti powder with the stoichiometry of a NiTi intermetallic compound.