Research And Optimizing Of Binding Properties Between WC-coating And Ti-6Al-4V Substrate

WC-17Co coatings on the surface of both Ti-6Al-4V and45steel werepreparated by HVOF technology, from the aspects of microstructure morphology、oxidation behavior、crack propagation form and mechanical property to research thereasons of interface failure between WC-17Co coating and substrate systematically.Using SEM analyzes the microstructure morphology of coating and substrate; acontrastive analysis in the oxidation behavior on the surface of substrate by usingXRD and XPS; three point bending and four point bending are adopted to measure themodulus of elasticity of coating and fracture energy release rate respectively.Rockwell hardness and microhardness are got by hardness tester. On the same time,using the method of peeling to test the value and distribution of residual stress incoated specimens along the direction of the coating thickness. The results show thatunder the same spraying process, the average of fracture energy release rate ofWC-17Co/Ti-6Al-4V and WC-17Co/45steel are234.43J.m-2and463.18J.m-2. Bycontrast, the reasons of low bonding strength of WC-17Co/Ti-6Al-4V are followingseveral aspects:1) Ti-6Al-4V has higher yield strength on the surface, high speedspray particles are difficult to produce plastic deformation to the surface, so particlescan’t bite with the substrate effectively;2) The surface of Ti-6Al-4V is oxidized hardlyby heat in the process of spraying, the oxydic-hard-brittle phase reduces the bondingstrength between coating and substrate;3) A higher residual stress inWC-17Co/Ti-6Al-4V and the maximum near the interface, when stressed on theinterface, residual stress is easy to form shear stress to promote the expansion of thecrack along the direction of the interface.In order to maximize the bonding strength of WC-17Co/Ti-6Al-4V, from twoaspects of surface roughening treatment and coating thickness to explore the iMPacton the bonding strength of WC-17Co/Ti-6Al-4V from surface roughness and residualstress.The results show:1)The higher surface roughness can improve the interfacebonding strength. but after reaching a certain value, the interface bonding strengthwill be reduced. The Rymaxis20.845μm when sand blasting process is60m/40Psi, WC-17Co/Ti-6Al-4V has a highest fracture energy release rate with259.0J.m-2at thismoment.2) The thicker coating can result higher residual stress in interface, and morelikely to cause crack extending along the direction of the parallel interface,So thelower the interfacial fracture energy release rate value of WC-17Co/Ti-6Al-4V. Bythe research, the best coating thickness is from0.21mm to0.21mm.