Structural and wear properties of heat-treated electroless Ni-P alloy and Ni-P-Si3N4 composite coatings on iron based PM compacts

In present study, the structural and wear properties of as-plated and heat-treated electroless Ni-P alloy and Ni-P-Si3N4 composite coatings on iron based powder metal (PM) compacts were investigated. The coatings were prepared using hypophosphite reduced alkaline electroless nickel bath. The synthesized submicron α-Si3N4 particles (10 g/l) were added into the Ni-P bath to develop Ni-P-Si3N4 composite coatings on the PM compacts. Coated compacts were heat-treated at 300, 400 and 500 °C, for 1 h and the effect of heat treatment on the coating performance was studied. Chemical composition of the coatings was analyzed by EDX. The phases and morphology of Si3N4 particles and coatings were examined by XRD and SEM. Phase transformation behavior was studied by differential scanning calorimetry (DSC). The wear properties were studied using pin-on-disc tribometer under unlubricated sliding conditions under a normal load of 40 N, sliding speed of 1 ms− 1 and sliding distance of 1000. The results show that the incorporation of submicron Si3N4 particles in the deposit significantly has been found to improve the hardness and wear resistance of composite coatings. The hardness and wear resistance of Ni-P and Ni-P-Si3N4 coatings heat-treated at 400 °C had the maximum hardness and wear resistance.