Microstructure And Properties Of Ni50A/WC Composite Coatings Prepared By Laser Cladding On H13 Steel

In order to solve the problem of surface wear failure of hot working die and easy cracking of cermet composite coating,the Ni50A/WC composite coating was prepared on H13 steel surface by laser cladding technology and orthogonal experiment to optimize the process parameters.The coating met the repair performance requirements and had no crack under the detection accuracy of X-ray diffraction micro-CT.Explores the cladding process parameters on the coating quality,the influence of the crack,the thickness of the cladding layer,by comparing with Ni50 A Ni50A/WC cladding layer,the cladding layers under different craft were analyzed by the organization and mechanical properties,reveals the structure evolution of WC on the impact of cladding layer cracking mechanism,for laser cladding metal ceramic composite coating crack inhibit provide theoretical guidance,The specific work and main conclusions are as follows:（1）The laser cladding process was optimized for Ni50 A and Ni50A/WC powder materials respectively by orthogonal experiment.The results show that laser power has the most significant effect on cladding quality and crack defects.With the increase of laser power,the continuity of cladding layer and crack defects are improved.The scanning speed has the most significant effect on the cladding layer thickness.The smaller the scanning speed is,the larger the cladding layer thickness is.When 1.5mm/s is selected,the cladding layer thickness is about 2mm to meet the repair requirements.（2）Ni50A coating is mainly composed of γ-Ni（Fe）solid solution ductile phase and Cr strengthened phase.Cr mainly exists in the form of Cr23C6 and Cr7C3 carbides.After the addition of WC particles,W element mainly exists in the form of WC and W2 C carbides after the microstructure evolution.These W and Cr carbides as hard phases significantly improve the physical properties of the coating.（3）W and Cr elements in the microstructure are enriched at grain boundaries,and the enrichment phenomenon of W element becomes more significant with the increase of THE content of W element dissolved into the microstructure.The enrichment phenomenon of W and Cr hard phase elements at grain boundaries causes element segregation and grain boundary embrittlement,which increases the cracking sensitivity of cladding layer.However,enrichment and embrittlement of grain boundaries of hard phase elements are not the dominant factors for cracking of Ni50A/WC coatings.（4）Part of W element will combine with Cr,C,Si and other elements to form eutectic compound precipitation.As the hard phase in the tissue is concentrated to form precipitation,soft and hard points appear in the cladding layer,and composition segregation occurs in the cladding layer.This phenomenon is one of the leading factors of cracking of Ni50A/WC coating.Therefore,promoting the diffusion of W element can effectively promote the uniform distribution of hardness of cladding layer and reduce the crack sensitivity.（5）WC has a high hard brittleability,and its thermal physical properties are quite different from γ-Ni（Fe）,so the WC particles are prone to crack defects.Cracked WC particles will form crack sources in the coating,leading to crack diffusion and extension of the coating.This phenomenon is one of the leading factors of cracking of Ni50A/WC coating.Therefore,promoting the dissolution of WC particles can effectively inhibit the generation of cracks.（6）The dissolution and diffusion behavior of WC particles is mainly affected by the laser line energy density.The process parameters are optimized.For example,in this study,the line energy density is increased from 544.6J/mm to 858.7j /mm,which promotes the diffusion and dissolution of W element and reduces the crack sensitivity of cladding layer.（7）The average microhardness of the optimized Ni50A/WC coating is 682.9HV,2.67 times that of the H13 steel matrix.The microhardness of all Ni50A/WC coatings is higher as they are closer to the middle bottom due to the sedimentation effect of WC.The wear amount of Ni50A/WC coating is only 12.1% of H13 steel.The friction and wear mechanism of H13 steel is adhesive wear,which changes to abrasive wear after Ni50A/WC coating is prepared by cladding.