Effect of powder feed rate on adhesion strength and microhardness of APS NiTi coating: a microstructural investigation

In the current investigation, an atmospheric plasma spray technique has been adopted to coat the NiTi material on the mild steel substrate. The coatings have been developed by varying powder feed rates. The microhardness and adhesion strength of the coatings have been evaluated and analysed. It has been observed that the microhardness and adhesion strength of the coating developed at 60 g min−1 depicted the best results. The coatings fabricated by low powder feed rates have evaporation, over melting and low deposition efficiency which leads to the decrease in microhardness and adhesion strength value. Furthermore, the coatings developed at a very high powder feed rate having a lack of heat transfer between plasma and particles and change in trajectories of the particles which leads to increase unmelted particle formation, porosity, and microcracks. This results in a decline in microhardness and adhesion strength of the coating.