Hardness, Friction and Wear Trends of Electroless Ni-W-P Coating Heat-Treated at Different Temperatures
The motive of this work is to analyze the effect of heating temperature on hardness along with wear characteristics of electroless Ni-W-P coating. In binary (Ni-P) coating, tungsten (around 5.22 wt%) is incorporated and heat-treated at 200, 400 and 800 °C for constant time period (1 h). Hardness and tribological tests are conducted on both as-deposited and heat-treated specimens. Hardness is found to be in a co-relative state with wear resistance for the present coatings. However, hardness as well as wear resistance decreases upon heat treatment at 800 °C. Ni-W-P coating is also found to display a quite low and stable COF value with testing duration. Microstructural analysis shows the morphology of the coating to be nodular. With heat treatment, the coating turns fully crystalline with the precipitation of harder Ni3P phases. At higher temperature, oxide formation over the coating is also observed. Both abrasive and adhesive wear mechanisms are found to govern the wear behavior of the present electroless Ni-W-P coatings. It is found that inclusion of tungsten promotes the tribological properties of Ni-P coatings even when subjected to high-temperature heat treatment.
KeywordsElectroless Ni-W-P Heat treatment Hardness Friction Wear
The first author would like to acknowledge the financial assistance and facilities provided by University Grants Commission (UGC), Govt. of India through Rajiv Gandhi National Fellowship.
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