Microstructure and hardness distribution of laser surface overlap coating layer

In the present work T15 high speed steel powder was coated on a low alloy tool steel by a laser surface overlap coating process to achieve a large area coating layer. The microstructure, composition, and hardness distribution of the coating layer were studied by optical microscope, scanning electron microscope, energy dispersive X-ray, and microhardness determinations. It was shown that the composition exhibited a heterogeneous distribution which was related to convection in the molten pool during the overlap coating process. The microstructure of the coating layer exhibited a periodic feature, and a periodic hardness distribution was present. The hardness of the coating layer was between 800 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 hardness distribution was obtained throughout the coating layer. (C) 1998 The Institute of Materials.