Tribological performance of electroless Ni-(high) P coatings under elevated testing temperature

Abstract

The ambient temperature is expected to play a significant role in the tribological performance of electroless Ni-P coatings. Moreover, the performance of Ni-P coatings is found to be largely dependent on the phosphorous content of the coatings. Hence, the present study aims to evaluate the tribological performance of Ni-(high)P coating under elevated testing temperatures. Both as-deposited as well as heat treated samples are developed for the performance evaluation. Coatings are tested under constant load and speed but at temperatures ranging from room temperature (R.T.) to 500°C. It is found that friction in general decreases at elevated temperatures compared to R.T. tests. Wear doesn’t show a consistent trend with change in test temperature. The wear rate of as-deposited coatings increases with increase in temperature up to 400°C test temperature beyond which it again decreases. In case of heat treated coatings, the wear rate remains almost same except at 200°C test temperature where a higher wear rate is observed. The hardness results show good correlation with the wear results. The as-deposited coatings are found to exhibit a higher increase in hardness after the tests compared to already heat treated coatings. The microstructure characterization of the coating is performed using SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-Ray Analysis) and XRD (X-Ray Diffraction Analysis). It is found that the coating in general exhibited a nodular structure and exhibit amorphous structure in as-deposited condition which turns crystalline with heat treatment. The wear mechanism is found to be predominantly abrasive in nature.