Study Of Forming Process And Mechanical Properties Of Ti15Mo Porous Structure Prepared By Selective Laser Melting

Ti15Mo alloy has excellent mechanical properties,corrosion resistance,fatigue properties and good biocompatibility,making it a new alloy with potential applications in the field of biomedical materials.Due to the high price of raw materials,traditional machining methods such as cutting and forging are used to manufacture structures with complex shapes,which have problems such as long manufacturing cycles,lack of guaranteed accuracy and serious waste of raw materials.The fact that human bone is a porous structure and the Ti15Mo alloy has a much higher modulus of elasticity than human bone.In order to simulate the porous structure in human bone and to reduce the modulus of elasticity of Ti15Mo implants,a triply periodic minimal surface(TPMS)porous structure was introduced.Based on these considerations,the formation of Ti15Mo alloys and the preparation of porous structures based on selected-area laser melting(SLM)is proposed.As the SLM method was introduced for the first time for the preparation of Ti15Mo alloys,the preparation process was systematically investigated.Three G,P,D uniform and gradient porous structures based on TPMS were prepared by SLM and the mechanical properties of the different structures were investigated.The main contents can be afforded as following:(1)The process parameters for SLM processing of Til5Mo alloy were optimized.At high scanning speeds(1400 mm/s),the melt pool profile becomes disordered and LOF(Lack of fusion)defects appear.As the scanning speed decreases,the distribution of the melt pool becomes more regular and the degree of remelting of the pool increases.At low scanning speeds(1200 mm/s),spherical defects form inside the melt pool and thermal cracks appears.A maximum density of 98.21%was obtained at the optimum processing parameters(1200 mm/s,175 W).The transformation of cellular crystals on the edges of the scanning channel toward the equiaxed crystals in the center of scanning channel is detected in XY plane.The cellular crystals at the boundaries of the molten pool and the columnar crystals radiating along the edge of the molten pool is observed in XZ plane.(2)The effects of different SLM processing parameters on the tensile properties of the specimens were investigated.Since the SLM processed Ti15Mo specimens retain a reasonable level of ?-phase,high density dislocations,finer grains and twin-induced plasticity(TWIP)internally,the tensile strength of Ti15Mo specimens processed under the optimum process parameters reached 840.41 MPa and elongation reached 32.37%.Through the analysis of fracture morphology,the difference of elongation of specimens under different parameters is the difference of defect types;The conversion of LOF defects to spherical defects can be improved by increasing the energy density appropriately;Through the analysis of microstructure under different strains,with the increase of strain,the density of twins increases thickness rises,and the width of twins is 7?m when the strain is 10%,4?m when the strain is 15%,and When the strain is 20%,it is 2?m.(3)The porous structures were prepared with the optimized parameters and analyzed by mechanical tests.The porous samples prepared are under the optimal parameters(1200mm/s,175W),the actual porosity differs from the designed porosity between 2.5%and 7.58%;The elastic modulus of the porous structure is between 3.27GPa-4.11GPa under the same porosity,which meets the requirements of human implantation;The yield strength of the P structure is the smallest,and the yield strength of the D structure is higher than the other two structures by about 31%;The gradient structure of G reduces the modulus of elasticity while maintaining the same yield strength;The three structures P,G and D deform differently during compression,with the uniform and gradient structures of P deforming in the same way,all collapsing layer by layer.The gradient structures of G and D were trapezoidal after compression;The uniform and gradient structures of D absorb the most energy within 60%strain,and the uniform and gradient structures of P have a clear onset of densification phase in the energy absorption efficiency curve.