English Title Study On Microstructure And Strengthening Mechanism Of Laser Cladding Ni25/WC Composite Coating

Ni25 alloy powder,commonly used in repairing glass molds,various molding molds and machine tool rails,is a kind of low hardness nickel-based self-melting alloy powders.In this thesis,Ni25 coating and Ni25/WC composite coating were successfully prepared by laser cladding technology,and coatings properties such as physical phase structure,microstructure,and wear resistance were studied.At the same time,in view of the steep mold surface repair,the phase composition,microhardness,friction and wear of the Ni25/WC coating prepared from the substrate surface at different angles were studied.The main research work of this thesis is as follows:（1）The effects of scanning speed on the morphology and quality of single-channel coating of single-channel Ni25 coatings was studied by laser cladding experiments.The optimal scanning speed process parameters were obtained by macroscopic and microscopic morphology,number of pores and grain size.（2）Using the above process parameters,Ni25 coating and Ni25/WC coating were prepared,the phase composition in the Ni25 coating is single,mainly composed ofγ-Ni,Ni₂B and a small number of Fe₃C phases,and the Ni25/WC coating is more WC and W₂C.The Ni25 coating has a large number of cytomeric crystals,branch crystals and secondary dendrites;the Ni25/WC coating is dominated by cytomeric crystals.Ni25/WC coating wear resistance is better than Ni25 coating,corrosion resistance is lower than Ni25 coating.Ni25coating to add a certain proportion of WC particles can effectively refine the coating grain size,improve wear resistance,but will affect the corrosion resistance of the coating.（3）The influence of different base angles on the single-channel morphology of the coating is significant,the section of the 0°coating section is symmetrical,the center of the90°coating section is offset to the downward side.The wear resistance of the 0°coating is better than that of the 90°coating,and there is no obvious difference in the microhardness and phase composition of the two coatings,but the wear resistance is significantly different,and the 0°coating is better than the 90°coating.90°coating in the cladding process,under the action of gravity,carrying gas and air resistance,the downward offset of the denser WC particles in the mixed powder is greater,and the large size of the WC particles that do not enter the molten pool is more,so that the WC particle content in the coating is reduced,thereby reducing the wear resistance of the coating.