Role of heat treatment on the friction and wear behavior of duplex electroless nickel deposits

Abstract

In the present investigation, duplex electroless Ni-P/Ni-Cu-P and Ni-P/Ni–W-P coatings are deposited on mild steel specimens using the dual bath technique. Both the coatings are developed with Ni-P as the inner layer. The scanning electron microscope (SEM), X-ray diffraction techniques (XRD) and energy dispersive X-ray analysis (EDX) are used to characterize the duplex coatings at pre and post-heat treatment state. Heat treatment is carried out at a temperature range between 200 °C and 800 °C. The surface morphology of the as-deposited coatings is nodular. Grain growth and grain boundaries are clearly visible in heat treated coatings. The EDX of Ni-P/Ni-Cu-P and Ni-P/Ni–W-P coating showed the phosphorus content as 12% and 9% respectively indicating high-P deposits. The copper and tungsten content of the coatings are 10% and 3% respectively. XRD analysis of both the as-deposited coatings indicate amorphous phase while heat-treated ones have crystalline phase structure. The crystalline structure increases the hardness of coating along with its wear resistance. The friction and wear behavior are assessed by a pin on disc tribometer. Overall, it can be seen that Ni-P/Ni–W-P system performs better compared to Ni-P/Ni-Cu-P in terms of friction and wear. However, heat treatment at higher temperature has negative impact on both the coatings as far as the tribological behavior is concerned.