A comparative study in microstructural and tribological aspects of phosphorus enriched electroless Ni-P and Ni-P-Cu coating

Abstract

Abstract The current article attempts to study the effect of different heat treatment temperature on mechanical (hardness) and tribological behavior (friction and wear) of phosphorus enriched Ni-P (EN-P) and Ni-P-Cu coatings. Inclusion of Cu (∼16 wt%) into binary EN-P (∼12% wt. P) coating is commenced an affect to its properties. The coatings are deposited on low alloy steel and heat-treated them at 400 °C and 600 °C for constant time duration i.e. 1 h duration. However, the rate of increase in heat treatment temperature is fixed at 10 °C/min for all coatings. Post deposition, the coatings (both as-plated and heat treated) are characterized by using energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Hardness and tribological tests are performed on Vicker’s microhardness tester and pin-on-disc tribotester respectively. For all types of coating, a typical nodular morphology is observed in SEM micrographs for as-deposited condition, while in heat treated condition coatings are appeared to be flat with an increase of nodule size. Heat treatment temperature has a vivid impact on coating microstructure. High-temperature heating at a constant period resulted in iron diffusion and oxide formation in coatings structure. Ni-P-Cu coatings exhibited lower hardness value for all heat treated conditions. In present study, maximum hardness (1085 HV0.1) is obtained for EN-P coating while heat treated at 400 °C for 1 h. Wear performances of the coatings are found to correlate with their hardness value. At 400 °C, both coatings shows best wear performances. But in comparison between EN-P and Ni-P-Cu, maximum wear resistance is exhibited by Ni-P-Cu coating (∼0.64 mm3/N-m).