Microstructure and Wear Resistance of Laser Cladded Ni-based Coatings with Nanometer La2O3 Addition

Ni-based coatings with nano-sized feedstock rare earth element (RE, La2O3) addition were produced by laser cladding. Bed of high energy ball milling mixed Ni60A and La2O3 powders were pre-placed onto the substrate 30CrMnSiNi2A before laser cladding. Results show that La segregates in inter dendrite and thus secondary dendrites growth and ripening are limited. The microstructure is refined. Top surface of the cladded coatings displays better refined microstructure which is caused by high La concentration, and this phenomenon is verified in EPMA results. The cracks and pores cannot be found in cladded coatings in which microstructure refinement and purifying effect caused by RE is clearly reflected in SEM microstructure, hardness and especially the wear resistance test results. The COF (coefficient of friction) of the coatings is apparently lower than that of substrate steel; the wear volume loss rate and the microhardness of coatings are less than 1/10 and about 4 times higher than that of substrate metal, respectively. This research forms the basement of metal surface anti-wear layer on the work surface of high speed heavy duty gear set in helicopter transform system.