Microstructure And Properties Of Surface Alloying Of TC4 Titanium Alloy With Cr And Mo By High Current Pulsed Electron Beam

To achieve surface alloying,high-current pulsed electron beam?HCPEB?equipment was used to irradiate the surface of TC4 titanium alloy pre-coated with Cr or Mo metal powder.The Cr-TC4 and Mo-TC4 systems were irradiated with 10,20 and 30pulses,respectively.The process of phases change,the evolution of microstructure and roughness on the alloyed surface of samples were investigated systematically with X-ray diffractometer?XRD?,optical microscope?OM?,scanning electron microscope?SEM?,3D laser scanning electron microscope?3D LSM?and transmission electron microscopy?TEM?.The microhardness of the specimens was tested by microhardness apparatus,the coefficient of friction and wear rate of the specimens before and after HCPEB alloying treatment were measured by friction-wear equipment.In addition,the corrosion potential and self-corrosion current density of the specimens before and after HCPEB alloying treatment were tested by electrochemical workstation.Meanwhile,the mechanism of variation of performance was also researched with characterization methods.After surface alloying by HCPEB,XRD pattern analysis of two systems?Cr-TC4and Mo-TC4 system?showed that Laves phase?Cr₂Ti?and intermetallic compound?Al₅Mo?were formed on the re-melted layer,respectively.And the phase composition of the surface layer transformed from?+?binary phases to??+?phases.The surface morphology?OM and SEM?characterization results showed that a large number of volcano-like craters were formed on the irradiated surface.The density of craters and surface roughness gradually decreased with the increasing number of pulses.The thickness of Cr-alloyed and Mo-alloyed layer were¹.5?m and 4?m after 30-pulsed irradiation.The TEM observations suggested that a large number of martensite structures and twin substructures were induced on the surface of the samples after HCPEB irradiation.The surface microhardness of Cr-TC4 and Mo-TC4 system was significantly improved compared with TC4 titanium alloy substrate.The enhancement of surface microhardness after HCPEB irradiation was mainly owing to the combined effect of solid solution,fine-grain and dispersion strengthening.Simultaneously,the surface hardness of the irradiated samples exhibited a rising trend with the number of HCPEB irradiation pulses increasing.Compared to the initial sample,the friction coefficient and wear rate of the alloyed sample were significantly decreased.In the meantime,the surface friction and wear performance was gradually improved as the pulse number increased,which is mainly attributed to the reduction of surface roughness and the enhancement of the hardness.After the surface alloying of TC4 with Mo by HCPEB,the oxide of molybdenum was more easily formed during the wear process,which possess significant friction-reducing performance.The comprehensive analysis revealed that the surface alloyed layer of Mo-TC4 system presented greater wear resistance than the Cr-TC4 system.The corrosion resistance significantly improved after surface alloying treatment.The enhancement of corrosion resistance was mainly due to the combination of the defects induced by HCPEB and the formation of second phase?Cr₂Ti or Al₅Mo?.In addition,the corrosion resistance of alloyed samples gradually improved with the number of irradiation pulses increasing.