Annealing effect on tribological resistance of electroless Ni-P/SiC nanocomposite coatings

In the present experimental work electroless Ni-P/Ni-P-SiC nanocomposite coatings is developed and the effect of heat treatment on the hardness and wear behavior of Ni-P/Ni-P-SiC nano-dispersion platings is discussed. The as-plated plating of Ni-P-SiC shows amorphous character of these platings. On heat treatment upto 6000C in steps of 2000C, the platings show decrease in amorphous character and enhancement in crystallization due to formation of intermetallics of Ni-P and Si-P alloys. Above 400°C grain growth in SEM images is also observed. These changes have been suggested to cause increase in hardness, friction coefficient and wear resistance of these platings. However grain growth in case of 6000C heat treatment results in lowering hardness which has been attributed to higher grain boundary area, as compared to amorphous state, formation of galvanic cells between Ni matrix and intermetallics, reduction in the amount of phosphorous in the plating and disbonding between the mild steel substrate and the plating because of their differential thermal expansions.