Effect of heat treatment on the microstructure and mechanical properties of electroless nickel-phosphorus coatings

Abstract

Electroless deposition have been considered as one of the most important nickelbased coating synthesization methods because of their coatings uniformity, high wear resistance, excellent corrosion and electrical properties. In this paper, nickel-phosphorus coatings were synthesized by electroless method on medium carbon steel substrates. The effect of heat treatment on the microstructure and mechanical properties of nickel-phosphorus coatings were investigated in detail. Structural analyses suggest that the coatings remain amorphous structure if the annealing temperature is below 400 °C. The crystalline Ni and Ni3P were formed in the coatings when the annealing temperature reach 400 °C and the grains grown significantly with increasing the heat treatment temperature from 500 °C to 800 °C. The mechanical properties of the nickel-phosphorus coatings display a significant change with the different heat treatment temperature. It was found that the highest microhardness value and the best wear resistance property has been obtained under heat treatment temperature of 400 °C. The possible mechanism of the relationship between microstructure and mechanical properties was also explored.