MICROSTRUCTURE AND HARDNESS DISTRIBUTION OF LASER-SURFACE OVERLAP COATING LAYER

In the present work T15 high speed steel powder was coated on a low al loy tool steel by a laser surface overlap coating process to achieve a large area coating layer. The microstructure, composition, and hardne ss distribution of the coating layer were studied by optical microscop e, scanning electron microscope, energy dispersive X-ray, and microhar dness determinations. It was shown that the composition exhibited a he terogeneous distribution which was related to convection in the molten pool during the overlap coating process. The microstructure of the co ating layer exhibited a periodic feature, and a periodic hardness dist ribution was present. The hardness of the coating layer was between 80 0 and 1000 HV(100 g). After temperature at 560 degrees C, the hardness level increased to similar to 1100 HV(100 g) and a more homogeneous h ardness distribution was obtained throughout the coating layer. (C) 19 98 The Institute of Materials.