Effect Of WC Addition On Microstructure And Properties Of Titanium-based Laser Cladding Layer

TC4 alloy has the advantages of high strength,excellent corrosion resistance,low density and strong machinability,and is widely used in aerospace,biomedical and marine engineering and other fields.However,the poor wear resistance and low hardness of TC4 alloy limit its application and promotion in complex friction conditions.Therefore,in this thesis,using TC4+WC as the cladding material,multi-layer lapped titanium-based wear-resistant composite coatings were prepared in situ on the surface of TC4 alloy by coaxial powder feeding laser cladding technology,and the effect of WC addition on the cladding layer was deeply studied.The influence law of macroscopic quality,microstructure and wear resistance,clarified the melting and resynthesis mechanism of WC in the coating,and revealed the precipitation mechanism of Ti C-coated WC mosaic structure phase,which is the laser cladding WC coating system on the surface of TC4 alloy.Provide scientific support,and lay a certain theoretical and technical foundation for the application and promotion of the wear-resistant coating of the system.The main research work of this thesis is as follows:(1)The effect of WC addition on the forming quality of titanium-based wear-resistant laser cladding layer was studied.The surfaces of the coatings with three different WC addition amounts were smooth without cracks;the addition of WC increased the thickness and dilution rate of the coating,and the change rules of the coating thickness and dilution rate were basically the same;when the addition amount of WC was 15wt%,voids appeared in the bonding area between the coating and the substrate.(2)The effect of WC addition on the microstructure of titanium-based wear-resistant laser cladding layer was clarified.The addition of WC will not affect the phase types of the cladding layer.The phases in the coating mainly include the reinforcing phase Ti C and the matrix phase α-Ti+β-Ti,and the coating also contains unmelted particles WC;With the increase of WC addition,the number of unmelted particles of WC increases,and the number of Ti C precipitation in the coating increases significantly,and the formed Ti C is mostly uniformly distributed in the coating in the form of granular and short rod-like phases;the reinforcing phase Ti C and unmelted particles WC form a coherent cladding mosaic structure phase,which inhibits the further melting of WC,resulting in the formation of refractory,residual and agglomeration phenomena.(3)The effect of WC addition on the microhardness and wear resistance of titanium-based wear-resistant laser cladding layers was revealed.Compared with the TC4 substrate,the addition of WC significantly improved the microhardness and wear resistance of the coating.Among them,the 15wt% WC coating had the highest microhardness(460～470HV0.5,about 1.38～1.41 times of the substrate)and the most excellent wear resistance,the wear rate is about 56.1% lower than that of the base material,and the wear mechanism is abrasive wear;in addition,the increase in the amount of WC increases the fluctuation range of the friction coefficient of the coating,and tribological properties fluctuate significantly,and the friction coefficient of the coating is larger than that of the substrate,which proves that the addition of WC cannot improve the wear reduction of the coating.