Effect of Al₂O₃ concentration on properties of Ni-W-Al₂O₃ composite coatings

Composite coatings of Ni-W-Al₂O₃ were prepared on 45^# steel substrate by direct current electrodeposition technology in electrolytic plating bath. The effect of Al₂O₃ particle concentration on wear and mechanical properties of composite coatings was investigated through microhardness, friction and wear testing machine and adhesion scratch tester. Surface and cross-section morphology of composite coatings were observed by SEM and XRD. The results show that Ni-W-Al₂O₃ composite coating presents crystalline structure, and its wear resistance is better than that of Ni-W coating. Increasing of the Al₂O₃ particles concentration in the electrolyte in a constant stirring rate will lead to a decrease first and then increase tendency in friction coefficient of composites coatings. The wear mechanisms of composite coatings are mainly adhesive wear and abrasive wear. Binding force of composite coatings and substrate is about 70~80 N which is fairly firm. The comprehensive performance of the composite coatings is the best when Al₂O₃ concentration is 5 g/L.