Study On The Microstructure And Mechanical Properties Of Lattice Ti-55531 Alloy Prepared By Selctive Laser Melting

In this paper,SLMed Ti-55531(Fe)alloy with RD,SC and OPT lattice structure were fabricated with the same laser parameters.Then,LPSA,XRD,SEM,quasi-static compression were used to investigate the effect of lattice structure types on the defects and mechanical properties of Ti-55531(Fe)alloy lattice components.Then different laser scanning speeds were used to fabricate the Ti-55531(Fe)lattice component with RD structure which has uniform deformation capacity.The effects of laser scanning speeds on the defects and mechanical properties were studied by using XRD,OM,SEM,XRT,density,hardness and quasi-static compression.The results are as follows:RD,SC and OPT lattice materials are comprised of only single ? phase,and the structure type has no effect on the phase constitutions.Compared with pure Ti,lattice Ti-55531(Fe)alloys with RD,SC and OPT structures show preferred growth in the bcc ? phase(211)crystal plane.The scanning speeds have no effect on the phase constitution of the lattice Ti-55531(Fe)alloy,but with the increase of the scanning speed,the ? phase peak shifts to the left and the lattice constant of ? phase increases.Lattice Ti55531 with different lattice structure exhibits different defect types.Lattice material with RD structure has lack of fusion hole defect,SC type lattice material has solidification hot crack.OPT type lattice material has solidification shrinkage hole.The porosity of RD lattice material is affected by the lack of fusion void.The solidification hot crack in SC lattice material and solidification shrinkage hole in OPT lattice material have no significant effect on the overall porosity of the material.Different scanning speeds have an effect on the types of internal defects in lattice materials.Defects of 20-80 ?m size are distributed in all lattice samples with different scanning speeds.With increase of scanning speed,the number of small defects in the range of 20-80 ?m decreases,but the unmelted defects in the range of 120-200 ?m can be observed.The surface morphology of lattice materials with different structure is different.The surface of RD type lattice material is rough,there are about 250 ?m toad back like morphology,and there are microporous defects in some positions.The width and radius of the weld pool on the surface of SC lattice sample are about 200 ?m,and there are solidification cracks on the edge of the weld pool.It exhibits uneven toad back morphology in the range of 160 ?m to 230 ?m on the surface and distributed on the hole wall of OPT lattice sample.The surface of the joint is smooth and there are solidification shrinkage defects.Different scanning speeds affects the surface roughness of lattice materials.With increase of scanning speed from 500 mm/s to 1500 mm/s,the surface roughness of lattice materials increases from 10 ?m to 30?m.The mechanical properties of lattice materials with different structures are different.The compressive strength and modulus of elasticity of RD lattice material are 27 MPa and 439 MPa respectively.The lattice material with RD structure deforms uniformly along the load direction,and the macro compressive crack is produced at the joint perpendicular to the load direction.The compressive strength of SC and OPT type lattice materials is higher than 90 MPa,but they all deform unevenly along the load direction.SC type lattice materials bend near the edge of lattice square grid,while OPT type lattice materials collapse near the edge of lattice circular grid stiffener.The reduction of scanning speed and the increase of input energy can greatly improve the compressive strength of lattice materials.When the scanning rate decreases from 1500 mm/s to 500 mm/s,the compressive strength of RD lattice materials increases from 23 MPa to 33 MPa.