Study On The Formability And Mechanical Behavior Of TC4 Titanium Alloy And Its Lattice Structure By Laser Selective Melting

The titanium alloy lattice structure is a kind of unique functional and structural integrated material,which is characteristic of light weight,high specific strength,good energy absorption,shock absorption and heat dissipation characteristics,thus it has great potential and application prospects in many fields such as aerospace and automobile industry.The traditional manufacturing process of lattice structure has high cost,long manufacturing cycle,and only some simple lattice structures,which seriously restricts the design and high-end application of lattice structure.The advantages of selective laser melting technology in processing complex precision structural parts open up new directions for the design and production of lightweight titanium alloy lattices.At present,a large number of researchers mainly focus on laser selective melting of bulk titanium alloy,but the research on laser selective melting of titanium alloy lattice is not mature at home and abroad.Therefore,in this paper,the formability of titanium alloy lattice structure formed by selective laser melting process is studied,which is based on the relatively mature process of TC4 titanium alloy material.The load bearing characteristics of titanium alloy lattice structure under quasi-static compression were tested.Firstly,the basic research on the selective laser melting of TC4 titanium alloy was carried out.By studying the microstructure characteristics,phase composition,microhardness,room temperature tensile mechanical properties and tensile fracture of the as-deposited sample,the process characteristics of laser selective melting of TC4 titanium alloy were obtained.It can be observed that a large amount of needle-shaped α’ martensite distributed in the original β grains,which has high strength and low plasticity.After heat treatment,the structure changes into lamellar structure composed of α+β phase,with less β content.With the increase of annealing temperature,the size of a phase gradually increases,and the content ofβ phase slightly increases.After heat treatment at 800℃/2h,the elongation increased from 7.33 ± 1.34%to 11.77 ± 0.36%,and the tensile strength decreased from 1371.03 ± 28.14 MPa to 1080.62 ± 21.02 MPa.The fracture mode was ductile fracture,and good matching of strength and toughness was obtained.Then,the research on the forming process of TC4 titanium alloy lattice was carried out,including model design,forming process simulation,and forming quality research.Seven types of BCC TC4 titanium alloy lattices with different apertures were designed,and the formability of TC4 lattice structure and the distribution of equivalent residual stress and deformation in lattice structures with different apertures were well predicted by simulation.Seven types of lattices with different apertures were formed.It was found that the main factors affecting the surface quality of TC4 lattice formed by laser selective melting are splatter,powder adhesion,slagging on the lower surface of the unit rod,and step effect.Finally,the laser selective melting of TC4 body-centered cubic lattice with several different apertures was studied,and its bearing characteristics and failure modes under quasi-static compression were studied,and its bearing characteristics were adjusted by heat treatment.It was found that the quasi-static compressive deformation process of the laser selective melting forming BCC type TC4 lattice can be divided into three stages:the elastic stage,the plastic energy absorption stage,and the collapse and collapse stage.The main failure modes of the deposited BCC type TC4 lattice are brittle collapse and shear failure at the maximum shear angle.The fracture occurred at the joint between the node and the unit rod,and it showed brittle fracture characteristics.Under the action of shear force,an initial crack is generated at the joint between the element rod and the node,and it expands to the node,and finally collapses and fractures rapidly under the action of axial tensile stress.The mechanical properties of the lattice are reduced under a large amount of weight loss.Through research,it has been found that the tensile strength and elastic modulus of the lattice increase almost linearly with the increase of the volume rate.The fracture mode of the deposited state is brittle fracture,and after heat treatment Later the fracture mode becomes ductile fracture.Heat treatment can significantly improve the plasticity of the BCC-type TC4 titanium alloy lattice.Therefore,the load-bearing characteristics of the laser selective melting forming BCC type TC4 lattice can be adjusted by adjusting the strength and plasticity of the lattice material through heat treatment.