Study of wear and friction of chemically deposited Ni-P-W coating under dry and lubricated condition

Abstract

In the present work, ternary Ni-P-W coating is deposited on mild steel substrates from an alkaline hypophosphite based electroless bath. The coatings are characterized in terms of their composition, phase structure and surface morphology using energy dispersive X-ray analysis, X-ray diffraction analysis and scanning electron microscope. It is seen that the coatings exhibit a mixture of X-ray amorphous and nanocrystalline nature in their as-deposited condition due to the co-deposition of tungsten and turns crystalline on heat treatment at 400 °C for 1h. A typical nodular surface morphology is observed in scanning electron micrographs. Microhardness and surface roughness of the coatings are also reported. Tribological characterization of the coatings are carried out on a pin-on-disc configuration tribo-tester by varying the test parameters namely the applied normal load, sliding speed and sliding duration with coefficient of friction and wear depth being the responses. The tests are carried out under lubrication as well as in dry condition to strike a comparison between the two environments. Wear depth is seen to increase with an increase in the applied normal load, sliding speed as well as sliding duration under lubricated condition. The variation of COF under lubricated condition is seen to be quite complex due to the synergistic effects of the tribo-testing parameters, lubrication, coating surface morphology and microstructure. A noteworthy improvement in the tribological behavior of Ni-P-W coating is achieved under lubricated sliding condition.