Microstructure and hardness distribution of laser surface overlap coating layer

Abstract

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 micro hardness 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 tempering at 560°C, the hardness level increased to ∼ 1100 HV (100 g) and a more homogeneous hardness distribution was obtained throughout the coating layer.