Red Hardness of Laser Cladded CoMoN/WC Composite Coating on W18Cr4V High Speed Steel

The CoMoN/WC composite coatings,synthesized by laser cladding of a layer of CoMoN/WC powders pre-coated on W18 Cr4 V high-speed steel substrate,were modified by quenching/tempering cycles.The influence of the tempering temperature and quenching-tempering cycle number on the microstructures,hardness and red hardness of the CoMoN/WC coatings were investigated.The preliminary results show that the tempering temperature had a major impact.To be specific,the tissue refinement,formation of Fe₃W₃C and interstitial compounds significantly increased the hardness of the coatings.As the tempering temperature increased(in three cycles),the hardness decreased,because high temperature increased grain-size and dislocation density.Formation of hetero-metallurgical bonding enhanced interfacial adhesion.The fact that many dendrites and some equiaxed-grains occupied the top,larger dendrites controlled the middle,and high density of pores and large black clusters dominated the bottom explains the depth profile of hardness.