LASER ALLOYING OF A GRADIENT METAL-CERAMIC LAYER TO ENHANCE WEAR PROPERTIES

The metallurgical structure, composition, hardness and abrasive wear resistance of a gradient layer were characterized following coating and melting of the layer by a CO2 laser. The results show that WC particles, used as hard ceramic phases, incorporated in the layer varied gradually in volume fraction from the surface to the substrate. In the region where the coating material connected with the substrate, a sosloid with good toughness was obtained. The layer produced had a uniform structure and excellent bonding with the substrate and was free of pores and cracks. The thickness of the layer is in the range 0.4-0.8 mm. The superficial hardness is about 1100 HV/0.2. The structure of the gradient layer processed by this method differed from those of conventionally laser-melted layers. The microhardness of the gradient layer varied smoothly acccording to the volume variation of the hard ceramic phases. Thus, it can not only improve the wear resistance of the layer but also avoid the production of cracks.