Selective Laser Melting Of Porous Titanium At Low Energy Density Preparation And Properties Study

Porous titanium is a porous metal material consisting of titanium or titanium alloy as the matrix and containing a large number of pores inside.In addition to the inherent characteristics of dense titanium,porous titanium also has the characteristics of small proportion,large specific surface area and excellent biocompatibility,and is widely used in the fields of biomedical,aerospace and catalyst carrier materials.At present,the traditional forming methods of porous titanium are mainly divided into powder metallurgy and physical or chemical synthesis.At present,many scholars have shown that the traditional method has some problems,such as high forming environment requirements,difficult to control the process,impurity of the specimen prepared and the need for special mold.The introduction of selective laser melting technology not only solves many constraints in traditional forming,but also provides a new way for the preparation of porous materials.In this paper,the preparation of porous titanium by selective laser melting technology and the study of the micromorphology evolution and mechanical properties of the obtained porous titanium were studied.The experimental scheme design of porous titanium,the micromorphology evolution and mechanical properties changes under different energy densities,pore characteristics analysis and pore forming mechanism exploration were carried out.The main research contents and conclusions are as follows:(1)The preparation process of porous titanium under low energy density was studied and the process window of preparing porous titanium by selective laser melting was obtained.The results show that porous titanium with porosity of 4.16～33.67%can be obtained at low energy density of 10.61～37.88J/mm~3.In addition,the forming porosity is larger when the energy density ranges from 10.61 to 27.78 J/mm~3,and the forming density is denser when the energy density ranges from 27.78 to37.88 J/mm~3.(2)The morphologies and mechanical properties of porous titanium with different energy densities were analyzed.The results show that a large number of incomplete melted powder particles can be seen in the porous titanium section prepared at low energy density.With the increase of energy density,the specimens change from slightly sintered neck connection to continuous fusion channel,and the pores change from irregularly connected holes to closed near-spherical ones.The phase composition of the forming specimen was mainlyαtitanium,and the microstructure was mainly elongated acicularα′martensite.The mechanical properties of Vickers hardness,tensile strength and compressive strength were analyzed.The results show that porous titanium with hardness of 38～312HV,tensile strength of 7.08～817.79MPa and compressive strength of 188～1260MPa can be formed at low energy density of 10.61～37.88J/mm~3.With the increase of energy density,the Vickers hardness,tensile strength and compressive strength of the forming specimens all showed a gradual increase trend.The reason is that the heat input increases,the molten pool fluidity in the forming parts is better,the powder particles melt into continuous molten channel,and the mechanical properties of the specimen are improved accordingly.(3)The pore characteristics and formation mechanism of porous titanium were investigated.The results show that the pores formed at low energy density are mostly micron level.When the energy density is small,the connected pores are dominant,and the closed pores are few.When the energy density increases,the closed pores are dominant,and the connected pores are few.According to pore morphology,the formed porous titanium pores are mainly divided into pore and keyhole.The porosity is caused by powder particles and the residual gas in the forming cavity or the evaporation steam in the molten pool.Keyholes are the result of incomplete melting powder particles,poor interweld bonding and insufficient interlayer penetration under low energy input.In this paper,a new preparation process for selective laser melting of porous titanium under low energy density is proposed,which reveals the changes in the morphology and mechanical properties of specimens under different energy densities,explores the pore characteristics and formation mechanism,solves many problems in the preparation of traditional porous titanium,and provides theoretical and experimental basis for the preparation of porous titanium specimens with other materials by selective laser melting in the future.