Research On The Microstructure And Properties Of Ti-6Al-4V Thin-walled Component Fabricated By Selective Electron Beam Melting

Selective Electron Beam Melting(SEBM),based on powder bed fusion technology,is a new additive manufacturing technology with features of high energy efficiency,high scanning speed,non-contamination due to high vacuum building environment,thus SEBM is suitable to fabricate reactive metals such as titanium alloy and possess tremendous applications in the field of aerospace,transportation and biomedical implant industries,etc.The typical preheating treatment of SEBM technology can lower residual stress in the component and lessen distortion of component manufactured by SEBM,hence SEBM technology is suitable to fabricate titanium alloy thin-walled component.At present,only the mechanical properties of standard bar-like samples were analyzed by literatures,while the mechanical results of standard thin-walled sample was lacked.And the analysis conducted on thin-walled sample were focused on as-built thin-walled samples,however,the research of effect of hot isostatic pressing as well as analysis for microstructure and mechanical properties of practical thin-walled construction component were rarely involved,which cannot guide the practical industrial manufacturing.This work fabricated thin-walled experiment samples and mechanical properties'testing was conducted on the thin-walled samples according to standard of GB/T228-2010.Meanwhile,the effect of building orientation on density,microstructure and mechanical properties of as-built thin-walled samples were researched using optical microscopy,scanning electron microscopy,and tensile testing machine.And the influence of hot isostatic pressing applied on thin-walled samples was investigated systematically by analyzing the microstructure and mechanical properties of SEBM-processed thin-walled samples.Finally,thin-walled construction component was manufactured by SEBM and the microstructure and mechanical properties of SEBM-processed thin-walled construction component was researched.The following conclusions are made:1.The densities of different locations in the SEBM-processed thin-walled samples were uniform,and the relative density achieved at 99.3%.The residual gas in the powders applied by SEBM equipment was the main reason for the drop of density.The microstructure of thin-walled samples fabricated by SEBM consisted of ?-? lamellar structure,acicular martensite(?')laths and grain boundary a phase which were included in the columnar grains.The tensile properties of SEBM-processed thin-walled samples with different building orientation all achieved the tensile standard of ASTM,and the tensile strength of thin-walled sample with vertical building orientation is higher than the samples with horizontal building orientation.2.After HIP treatment,the relative density achieved at 99.8%due to the elimination of defects in the samples,and the microstructure became uniform by the decomposition of ?' martensite.Elongation was raised with the slightly drop of tensile strength after HIP treatment.The high cycle fatigue strength of SEBM-processed thin-walled samples is 550MPa,which was comparable to sheet undergone rolling and annealling.3.Ti-6Al-4V thin-walled component(length:214mm,width:78mm,height:175mm,thickness:3-4.5mm)was fabricated successfully by SEBM technique.Average ultimate tensile strength of SEBM-processed thin-walled construction component was 1005 MPa,which is 12%higher than rolling Ti-6A1-4V strength standard of ASTM.Average hardness of SEBM-processed thin-walled construction component was 346HV,which was comparable to the hardness of casting Ti-6Al-4V standard of ASTM.