Wear mechanisms of Ni-W and Ni-W/Al2O3 composite coatings sliding against Si3N4 and AISI 52100 steel counterbodies

Abstract

In this work, wear mechanisms of electrodeposited Ni-W and Ni-W/Al2O3 coatings sliding against Si3N4 and AISI 52100 steel have been comparatively studied. For both Ni-W and its composite coatings sliding against Si3N4, worn morphology shows the tribochemical reaction (tribooxidation) followed by abrasive wear is the dominated mechanism. Comparing with Ni-W coatings, the protective oxide layer is slower peeled off at tribooxidation stage and wear debris are easier squeezed on the Ni-W/Al2O3 during abrasive wear stage. The incorporated Al2O3 provide load bearing effect during microploughing and improve the wear resistance. As sliding against AISI 52100 steel, wear rate of Ni-W/Al2O3 is several times higher than that of Ni-W coatings. Conformity between surfaces of the Ni-W coating and counterbody leads to mild smoothening wear, while the plastic deformation dominated delamination makes severe wear of Ni-W/Al2O3. Deformation resistance of the coatings and transition of counterbodies materials from ceramic to hard metal are responsible for the different wear mechanisms. For Si3N4 ceramic, low thermal conductivity leads to tribooxidation followed by abrasive wear of both Ni-W and Ni-W/Al2O3 coatings. Relatively high deformation resistance of Ni-W coatings is responsible for the conformity as the premise for mild wear sliding against AISI 52100. Low deformation resistance of composite coatings induced by weak interfaces between Al2O3 and Ni-W matrix makes delamination sustained.