Microstructure And Properties Of Laser Cladding WC-Co Composite Coatings On Titanium And Titanium Alloys

For many years,titanium and its titanium alloys have been widely recognized in the automotive,aerospace,marine,pharmaceutical,chemical,and energy industries due to their high specific strength,low thermal expansion coefficient,and excellent corrosion resistance.Among the titanium alloys,Ti-6Al-4V alloy is mainly used as a general-purpose alloy.However,despite its numerous applications,its use is limited due to its poor hardness and wear resistance.At present,enhancing the tribological properties of titanium alloys is the main research direction in many application fields.Various surface modification methods have been proposed to meet different needs.Among them,laser cladding is an effective method for manufacturing precise and defect-free cladding layers of dissimilar materials to obtain a highly wear-resistant surface.In view of the problem of poor wear resistance of TA2/TC4,the laboratory-made WC-12Co and WC-25Co powders were selected,and different laser process parameters were used to prepare wear-resistant coatings on the surface of TA2/TC4 titanium alloy.Scanning electron microscopy,energy spectrum analyzer,hardness tester,high temperature friction and wear meter to study the microstructure and mechanical properties of the coating,and analyze the phase composition,microstructure,hardness and wear resistance of the cladding layer with different powders and different process parameters With the influence of performance,the best process for preparing WC-Co composite coating by laser cladding on the surface of titanium alloy was obtained.Analysis of the laser cladding coating on the surface of TC4 revealed that a good metallurgical bond can be formed at the interface between the coating and the TC4 substrate,and the interface is clean.After many tests,it was found that when the Co content is 12%,the high melting point cladding composite powder is easy to deposit to the bottom of the molten pool due to the high density,which causes the ceramic particles in the coating to gather at the bottom of the cladding layer,and there are different degrees of cross section Holes.When the Co content increases to 25%,the increase in the binder Co contributes to the adhesion of the coating and the substrate.The powder deposition phenomenon does not occur in the cladding layer,and the cladding layer has a good morphology.When the laser power is 1300W,the WC-25Co cladding layer on the TC4 substrate has a good morphology.New hard phases TiC and CoTi2 are mainly distributed in the cladding layer,of which TiC exists mainly in the form of dendrites.The microhardness of the cladding layer is 2-4 times higher than that of Ti-6Al-4V matrix(360HV),and the maximum hardness reaches 1349 HV.Under the same dry sliding wear conditions,the wear resistance of the WC-25Co coating is significantly improved,which is 15.7-34.1 times that of the substrate.Analysis of the laser cladding coating on TA2 surface,when the laser power is P=1300W,the organization in the coating is uniform and dense,and the WC-25Co cladding layer forms a good metallurgical bond with the substrate.The composite material layer mainly includes TixC1-x(TiC,Ti8C5),WC,W2C,TiWC2,CoTi2,Ti.Among them,WC and the TiC phase generated in situ are the main reasons for the improvement of the wear resistance of the cladding layer.The hardness of the cladding layer is 5-7 times higher than that of the TA2(200HV)substrate.The wear resistance of the cladding layer is significantly improved.The overall hardness improvement of the TA2 cladding layer is more obvious than that of the TC4 cladding layer.The main reason is that there are more hard phases TixC1-x in the TA2 cladding layer.