Improvement in tribological behavior of novel sol-enhanced electroless Ni-P-SiO2 nanocomposite coatings

Abstract

Homogeneous nickel-phosphorus-silica (Ni-P-SiO2) nanocomposite coatings were prepared on low carbon steel alloy surfaces by a new process. This method was developed by combining sol-gel and electroless deposition technique in the presence of surfactant to produce a composite coating containing well-dispersed SiO2 nanoparticles. The SiO2-sol solution was directly added to the electroless Ni-P solution to produce nanocomposite coating on the St37 steel substrate. The surface morphology and composition analysis were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS), which confirmed the presence of silica in the coating matrix. The results showed co-deposited SiO2 nanoparticles with a clean surface and no agglomeration. Therefore, this technique can effectively avoid the agglomeration of nanoparticles in the coating matrix. The structural phase analysis indicated that by heat treating, the amorphous phase changed to crystalline phases such as Ni, Ni3P and some non-equilibrium phases. The microhardness and wear properties of Ni-P and Ni-P-SiO2 composite coatings were evaluated and compared with each other. The hardness and wear resistance of Ni-P composite coatings increased in the presence of SiO2 nanoparticles, whereas the maximum microhardness of 970 Hv100, minimum coefficient of friction of 0.25, and minimum wear loss of 4.4 mg were achieved in heat treated coating at 400 °C for 1 h