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

Abstract

Abstract 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. A comparison 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 micro-hardness, 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 micro-hardness 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 53.55 HV0.2 to 71.31 HV0.2 for non-textured samples and 70.47 HV0.2 to 113.52 HV0.2 for textured ones. It varied from 53.68 HV0.2 to 68.85 HV0.2 for non-textured surfaces and 63.03 HV0.2 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.