Influence of laser cladding on the surface hardness of small-diameter metallic wire substrates

In this study, a laser beam is used to clad stellite or cermet on various metallic wires. One aim is to realize a coating with a high volume compared with that of the substrate (ratio about 1/5) without the use of auxiliary cooling. The thermal treatment induced during the coating can modify the properties of the wire, for instance the restoration of the structure of the initially cold drawn wire. This change of structure depends on the temperature reached in the wire and on the cooling rate. In order to control the heat-affected zone (HAZ) in the wire, the thermal gradient in the cross-section is calculated under the laser beam, and results are correlated with microhardness profiles. It is shown that the HAZ is limited by the temperature of restoration, beginning at about 1300 K.