Effects Of Laser Shock Peening On Microstructure And Mechanical Properties Of Ti-6Al-4V Titanium Alloy Fabricated Via Electron Beam Melting

Electron Beam Melting(EBM)is an additive manufacturing technology that uses high-energy electron beams as a heat source to melt and solidify alloy powders and stack them layer by layer.It has the advantages of compact products,automated and batch production of complex geometric structural parts.Ti-6Al-4V titanium alloy has high specific strength,excellent corrosion resistance and biocompatibility,and can be widely used in aerospace engineering,medical and petrochemical industries.However,in the process of manufacturing Ti-6Al-4V samples by EBM technology,there are still phenomena such as coarse columnar crystals and residual tensile stress,which affect the mechanical properties of the material,especially the fatigue properties.Laser shock peening(LSP)is an advanced surface treatment process that uses high-energy short-pulse laser beams to plastically deform the sample surface and introduce residual compressive stress,which can improve the tensile and fatigue properties of the material.Therefore,LSP treatment has great potential as a post-treatment process for additive manufacturing,which can improve the mechanical properties of additive manufactured parts.In this study,Ti-6Al-4V alloy was selected as the manufacturing raw material,and LSP treatment was used to strengthen Ti-6Al-4V parts manufactured by the electron beam melting.The effects of LSP on the microstructure,residual stress,and mechanical properties of EBM manufactured Ti-6Al-4V samples was investigated.The strengthening mechanism of LSP on the mechanical properties of EBM manufactured Ti-6Al-4V samples was discussed.The microstructure and phase composition of the EBM manufactured Ti-6Al-4V specimen before and after LSP treatment were studied by means of optical microscope,X-ray diffractometer,scanning electron microscope and transmission electron microscope.Vickers hardness tester was used to test the hardness distribution before andafter LSP treatment.The universal test machine and fatigue test machine were used to test the tensile and fatigue properties of the samples before and after LSP treatment,and the SEM fracture morphology was analyzed.The research results show that after LSP treatment,the microstructure of the Ti-6Al-4V specimen manufactured by EBM is significantly refined,and the initial ? + ?lamellar structure is transformed into a gradient composed of nanocrystals,twins,and submicron grains structure.After LSP treatment,the residual stress state of the surface layer of the sample was changed.The compressive residual stress generated by LSP treatment reached-380 MPa,and the depth of the affected layer could reach 450 ?m.After the LSP treatment,the microhardness of the sample is increased by 11%,and the depth of the affected layer can reach 900 ?m.The tensile tests show that the ultimate tensile strength of the samples manufactured by EBM has been increased by about 5% after the LSP treatment,and could maintain considerable ductility.The high-cycle fatigue test results of EBM samples showed that the fatigue strength of the samples after LSP treatment increased by about 17%.The significant improvement in tensile strength and fatigue strength of Ti-6Al-4V specimens manufactured by EBM after laser peening can be attributed to the effect of compressive residual stress and the grain refinement.These research results will provide a theoretical guidance for improving the fatigue performance of additive manufacturing materials,and also show that LSP treatment has extremely high application potential and adaptability as a post-treatment process for additive manufacturing.