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

Cu substrates were laser-clad with a Ni-based powder using a CW-CO2 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 similar to 1.3 GPa. The high hardness of the Ni-based cladding is due to a microstructure consisting mainly of Ni dendrites and Ni and Ni3B 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 similar to 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. (C) 1999 Elsevier Science S.A. All rights reserved.