Electroless Ni-P-MoS₂ composite coating of Al-alloys: effect of surface textures and bath composition

The present work assesses the effect of textures and bath composition on Ni-P-MoS2 electroless composite coating. Aluminium alloys are subjected to textures (through electrical discharge machine) for using as substrate material in the present context of study. Acomparison study is conducted to evaluate the effect of coatings on textured and non-textured surfaces prepared in two different baths (oxalic acid and hydrazine). Different surface characterization has been carried out including microhardness, surface roughness, topography, morphology, tribology through micro-scratch test, and composition analysis (using Energy Dispersive Spectroscopy) in the study. Results indicate that the textured coated surfaces impart better wear-resistant properties than those of coatings produced in non-textured ones. Moreover, the coating prepared using oxalic acid bath imparts better microhardness and tribological properties than those of hydrazine bath. The elemental presence of Mo, S, Ni and P was affirmed through EDS mapping, indicates transference of MoS2 particles on to the coated surfaces. The micro-hardness of different coated specimen prepared using oxalic acid bath range from 53.55HV(0.2) to 71.31HV(0.2) for non-textured samples and 70.47HV(0.2) to 113.52HV(0.2) for textured ones. It varied from 53.68HV(0.2) to 68.85HV(0.2) for non-textured surfaces and 63.03HV(0.2) to 98.27 HV0.2 for textured surfaces in hydrazine bath. The addition of MoS2 powder in the electroless bath account for the deposition of a tribo-adaptive layer on Al-alloys.