Synergistic effect of ferrous sulphide and MWCNT on wear behaviour of HVOF-sprayed nickel/graphite composite coatings

This work presents a novel composite formulation for industrial-grade nickel graphite reinforced with ferrous sulphide and multi-walled carbon nanotubes, which were sprayed using HVOF on mild steel substrates. The tribological performance was assessed with a pin-on-disc setup at room temperature and ambient air, varying load (10 N, 20 N, and 30 N) at a constant speed, and varying speeds (100 rpm, 200 rpm, and 300 rpm) at a constant load. Additionally, three-dimensional optical imaging was used to evaluate surface roughness of the HVOF-coated samples before and after testing. Compared to other compositions, the sample containing 50 % NiGr, 49 % FeS, and 1 % MWCNT performed best, exhibiting the highest wear resistance and lowest coefficient of friction (COF). To establish a correlation with the wear data, the worn HVOF-coated samples underwent SEM-EDS elemental mapping analysis. The incorporation of MWCNTs and ferrous sulphide into the nickel-graphite matrix enhanced load distribution and minimized surface roughness, resulting in markedly improved wear resistance and a reduced coefficient of friction. This marks a notable advance in the tribological performance of coatings. Moreover, the study conclusively demonstrates that the composite of NiGr, FeS, and MWCNT offers an excellent option for applications requiring superior wear resistance and durability.