Effect of particle size on surface roughness and morphology of heat-treated electroless Ni-YSZ coating

The paper discusses the surface characterisation of electroless nickel-yttria-stabilised zirconia (Ni-YSZ) coating with varying YSZ particle sizes and undergoes heat treatment at a temperature between 300-400°C for 1-2 hours for wear resistance purposes. This finding will be helpful to the application of Ni-YSZ as an alternative coating for cutting tools. The surface characterisation was analysed using JOEL Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray (EDX) JSM 7800F. The crystallographic structure of materials was analysed by X-ray diffraction (XRD) Bruker D8 Advance instrument. The Ni-YSZ coating was deposited using electroless nickel co-deposition of 8YSZ ceramic particles with a nano, mixed and microparticle sizes onto a high-speed steel (HSS) substrate. The coatings were heat treated at temperature 300-400°C and time 1-2 hours. The surface roughness was measured using Mitutoyo surface roughness tester SJ-301. The electroless Ni-YSZ coating deposited has an average thickness of 30 µm. It is found that the coating morphology electroless coating without YSZ particle incorporation (EN) and Ni-YSZ nano (N) is smoother compared to the Ni-YSZ mixed (NM) and Ni-YSZ micro (M). The EDS composition analysis shows the YSZ content in the electroless Ni-YSZ coating for N samples is the lowest, whereas NM samples are the highest. This resulted in the surface roughness behaviour where the mixed-size YSZ particle gives the highest roughness at all temperatures. The XRD analysis shows that heating temperatures above 300°C caused the precipitation of Ni3P crystalline. Previous studies in the surface characterisation of electroless nickel composite are scarce; thus, the study has limitations in finding supporting data. The surface characterisation especially related to the surface roughness of the electroless nickel, either the Ni-P or composites or alloys are rarely reported. Thus, this study enlightened the effect of particle size on surface roughness and morphology of heat-treated coatings.