Microstructure and tribological properties of Ni-based claddings on Cu substrates

Abstract

Cu substrates were laser-clad with a Ni-based powder using a CW–CO 2 laser. In order to obtain sufficient absorption of the laser irradiation by the substrate a Ni–B–Si plasma-sprayed layer was deposited on the Cu substrate and remelted prior to the cladding process. High hardness values in the range of 5 to 5.4 GPa were achieved for the laser-clad Cu surfaces, compared with a Cu substrate hardness of ∼1.3 GPa. The high hardness of the Ni-based cladding is due to a microstructure consisting mainly of Ni dendrites and Ni and Ni 3B lamellae. However, the large number of brittle boride phases at the interfaces between the cladding, the plasma-sprayed layer, and the substrate causes cracks during cooling owing to high thermal stresses. Tribological tests of the claddings reveal poor adhesive friction and wear properties with a tendency to seizure when sliding against steel under dry conditions. Abrasive wear coefficients of ∼0.1 were obtained for the claddings when abraded by #320 emery paper. Some correlation was found between the cladding thickness and the tribological properties due to thickness induced defects in the cladding.