Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.