Phase transformation, thermal stability and indentation behavior of sputtering Ni-P-based interlayer enhanced CrN composite coatings

In this study, CrN top coating with NiP and NiPAl alloy interlayers were fabricated by sputtering technique. The microstructure of the CrN/NiP-based composite coatings was controlled by process temperature during sputtering and post annealing procedures. The alloy NiP and NiPAl interlayers remained an amorphous feature as CrN top coating was deposited at 350 °C. The higher CrN deposition temperatures hastened the crystallization of the NiP-based interlayer significantly. The NiPAl interlayer exhibited a higher crystallization temperature of 450 °C as compared to that for binary NiP ones. Not only could the addition of Al in NiP layer increase the thermal stability of the composite coatings, but also improve the thermal resistance during CrN coating deposition. Through indentation behavior analysis, significant creep behavior was observed when the microstructure of the interlayer was amorphous or fully crystallized. On the other hand, under proper heat treatment, the creep phenomenon of the composite coatings was suppressed by the precipitation and crystallization of the NiP-based interlayer.