Electron Beam Cladding Of Titanium Alloy Surface And Its Welding With Titanium Alloy

TC4 titanium alloy has excellent corrosion resistance,high specific strength,good creep resistance,and biocompatibility,and has been widely used in aerospace,medical,military,and energy industries.With the continuous development of the industry,the hardness and wear resistance of TC4 titanium alloy gradually cannot meet the performance requirements of new special materials,which limits the application of TC4 titanium alloy.Therefore,surface modification of TC4 titanium alloy is of great significance.In this experiment,the Al Co Cr Fe Ni Ti_0.5 HEA coating was deposited on the TC4 substrate using an electron beam,and then the coated TC4/TC4 and TC4/TC4 were butt welded using an electron beam to obtain excellent welded joints.The process parameters of electron beam cladding were optimized through orthogonal experiments.According to the hardness of the HEA coating,the optimal parameters were determined as follows:accelerating voltage:65 k V,welding beam current:22 m A,and scanning time:4 s.Under this parameter,the surface hardness of the HEA coating reaches a maximum value of 859 HV.By observing the microstructure of the HEA coating under this parameter,it can be clearly found that the HEA coating has no cracks,holes,and other obvious defects.The HEA coating is well formed and has a good bonding with the substrate.At this time,the coating has the best molding effect.The microstructure of the HEA coating was observed and analyzed.The HEA coating mainly consists of FCC and BCC phases.The diffraction peaks of the FCC phase are consistent with Al Ni₂Ti or Al Co₂Ti,while the BCC phase is consistent with Fe-Cr.The interior of the HEA coating is well formed,with uniform organization,free of cracks,holes,and other defects,and its surface is flat and smooth.The IR phase is mainly composed of Fe and Cr elements,corresponding to the BCC phase.The DR phase composed of Al,Co,and Ni is an equimolar FCC phase with an Al Ni₂Ti（or Al Co₂Ti）structure.The microhardness of the HEA coating was measured using a Vickers hardness tester.The average microhardness of the HEA coating was calculated to be 782.2 HV_0.2,approximately 2.6 times that of the TC4 substrate(305.6 HV_0.2).Friction and wear experiments were conducted on TC4substrate and HEA coating,and their average COF were 0.48 and 0.57,respectively.The friction and wear process is divided into initial wear stage and stable wear stage.The COF of the HEA coating and TC4 substrate becomes stable in about 700seconds.The wear amount of the HEA coating is 0.0657 mm³,approximately one tenth of the TC4 substrate wear amount（0.6112 mm³）.The TC4 substrate has been confirmed to exhibit abrasive and oxidative wear characteristics.The HEA coating exhibits adhesive and oxidative wear characteristics.Based on the comprehensive analysis of the morphology of the welding sample and the tensile strength of the tensile sample,the optimal electron beam welding parameters were obtained:welding voltage:65 k V,welding beam current:22 m A,welding time:4 s.Electron beam butt welding experiments were conducted under the optimal process parameters to analyze the microstructure and element content of the joint.The welded joint with coating TC4/TC4 mainly consists of Al Ni₂Ti（Al Co₂Ti）and Fe-Cr.The welded joints of TC4/TC4 are mainly composed ofα/α’Phase composition,there are stillβPhase and a small amount of Ti C.The hardness of welded joints was measured and the morphology of tensile fractures was analyzed.The microhardness of TC4/TC4 welded joints with coating was significantly higher than that of TC4/TC4 welded joints.For coated TC4/TC4 welded joints,the maximum hardness in the weld zone is 578 HV_0.2,and the maximum hardness of TC4/TC4 welded joints is 420 HV_0.2.The tensile fracture of TC4/TC4 was analyzed,and the fracture surface was characterized by ductile dimples.The tensile fracture of coated TC4/TC4 was analyzed.The tensile fracture was located in the weld zone,and the fracture was relatively flat and bright,showing radial or crystalline morphology.The fracture surface exhibits brittleness with typical cleavage fracture characteristics.