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

Abstract

Abstract In present study, the structural and wear properties of as-plated and heat-treated electroless Ni-P alloy and Ni-P-Si 3 N 4 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-Si 3 N 4 particles (10 g/l) were added into the Ni-P bath to develop Ni-P-Si 3 N 4 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 Si 3 N 4 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 Si 3 N 4 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-Si 3 N 4 coatings heat-treated at 400 °C had the maximum hardness and wear resistance.