Nanoparticle Concentration and Heat Treatment Effects on Microstructure and Tribological Behavior of the Ni-P Nanocomposite Coating

The aim of this study was to create electroless Ni-P-SiO۲-MoS۲ nanocomposite coating and investigate the effect of the concentration of nanoparticles and heat treatment on its structure and tribological behavior. To achieve this purpose, MO۴۰ steel specimens were coated at the temperature of ۹۰°C in electroless nickel-phosphorus coating baths containing different concentrations of ۳, ۷, ۱۱, and ۱۵ g/L of SiO۲ and MoS۲ reinforcement nanoparticles with pH ۶.۴ for ۶۰ minutes. Then, the coated sample containing ۷ g/L of nanoparticles was subjected to heat treatment of ۴۰۰°C for ۶۰ minute. To investigate the microstructure, tribological behavior, elements’ weight percent and phases in the coatings, FE-SEM images were observed and wear test, EDS and XRD analysis were performed, respectively. Results showed that by increasing the concentration of nanoparticles in the coating bath, the weight percent of the reinforcement elements in the coating increases. Exceeding concentration of nanoparticles from certain value leads to the agglomeration of the coating particles and creation of porosity which results in a non-uniform coating with low protecting properties. Therefore, the appropriate concentration of nanoparticles in the coating bath was chosen ۷ g/L, because the results show a uniform coating of the amorphous nickel phase and the SiO۲ and MoS۲ nanoparticles. Subsequently, the heat treatment results showed that the amorphous nickel phase formed in the coating became into two crystalline nickel and Ni۳P phases after heat treatment that leads to increase wear resistance.

Keywords:

Electroless Ni-P coating , Nanocomposite , Nanoparticle concentration , Wear resistance