Laser cladding Mo-based coatings on copper alloys to improve the current-carrying tribological properties of Cu/Al friction pairs

To enhance the current-carrying tribological properties of the Cu/Al friction pair, Ni-based transition-coatings and Mo-based function-coatings were sequentially prepared on copper alloys by laser cladding. The microstructure, mechanical properties, electric conductivity, and current-carrying tribological properties of the coatings were comprehensively investigated. The function-coating consisted of a Mo-rich layer and a high-dilution layer, with a close metallurgical bond formed between the layers. Compared with the substrate, the average microhardness (640.2 HV0.2) and elastic modulus (320.9 GPa) of the Mo-rich layer were increased by 326.8 % and 89.7 %, respectively. The substrate after cladding with the Mo-based coating demonstrated an acceptable conductivity as 78.30 %IACS. The transition-coating infiltrated moderately into the function-coating, promptly filling cladding defects, enhancing grain boundary toughness, and effectively mitigating the significant mechanical property differences between the Mo-rich layer and the substrate. Current-carrying friction tests with the Al friction pair indicated that, under low currents (10 A), the Cu substrate was prone to both adhesive wear and abrasive wear, while the function-coating only exhibited slight abrasive wear. Under high currents (40 A), the Cu substrate experienced severe mechanical wear and electrical wear. Nevertheless, the function-coating still suffered slight abrasive wear with a wear volume of only 1/33 of the substrate owing to the protection and lubrication of the Al adhesion film and the good contact state.