| With the advantages of high specific modulus,high specific strength,light weight and energy absorption,metallic Multi-lattice Structure have great potential for applications in transportation,aerospace and biomedical fields;meanwhile,the rapidly developing additive manufacturing technology in recent years can effectively improve the precision and designability of Multi-lattice Structure,which provides new methods for the research and application of metallic lattice materials and promotes the development of lattice materials.However,the current research mainly focuses on the lattice structure obtained from a single type of cell array,and rarely considers the influence of the arrangement in the lattice structure composed of different types of cells on the mechanical properties of the structure,while less taking into account the influence of the laserselective melting process on the forming quality of titanium alloy lattice.Therefore,in this study,a heterogeneous lattice structure formed by different combinations of cells was been designed,and investigated the mechanism of the influence of the selected laser melting process(SLM)on the heterogeneous lattice structure of titanium alloy with titanium alloy powder as the raw material and explored the optimization method of the process,and evaluated the mechanical properties of the structure through quasi-static compression experiments and finite element analysis.The mechanical properties of the structure are evaluated through quasi-static compression experiments and finite element analysis to provide a technical basis for lightweight design and application.Up to now,the research contents and results of this paper are as follows:(1)The effect of laser selected zone melting process(SLM)regulation on titanium alloy specimen forming.According to the previous research,three variables of laser power,scanning speed and powder layer thickness were selected and then a three-level,threefactor response surface design experiment was carried out to prepare titanium alloy specimens using different combinations of process parameters,the reliable mathematical model of the response of different process parameters to the cylindricity and rod diameter of SLM formed specimens was established.The optimal combination of laser power,scanning speed and powder layer thickness was determined,and the process optimization was realized.(2)By observing and comparing the rod diameter of SLM formed micro-rod at different tilt angles,it was found that the slagging phenomenon caused by powder particle aggregation occurred on the side and lower surfaces of micro-rod for both tilt angles,resulting in the actual rod diameter of micro-rod generally larger than the design value,and the larger the tilt angle,the flatter the surface shape of micro-rod.At the same time,the surface morphology of the selected area laser melting titanium alloy material was analyzed,and it was found that there were fish scale pattern phenomenon,as well as spheroidization,spalling and cracking defects in the specimen,and the improvement methods were proposed for the defects.(3)The design of titanium alloy heterogeneous lattice structure and simulation study of forming process were carried out.Based on the biological principle,the design of multiple types of Multi-lattice Structure,which are a combination of body-centered cubic(BCC)and face-centered cubic(FCC)unit structures,was carried out;the distribution and state of equivalent residual stress and deformation of titanium alloy Multi-lattice Structure were predicted by simulation,and the mechanism of the influence of process parameters on the forming of lattice structures was analyzed by combining the thermal diffusion effect.Based on the previous study,the heterogeneous lattice structure specimens were prepared and the surface quality of SLM formed lattice structure was further evaluated under the optimal combination of process parameters of 260 W laser power,600mm/s and 40μm powder layer thickness.(4)To study the effects of different cell hybrid arrangement patterns on the deformation behavior and load-bearing capacity of the dot-matrix structure.Through quasi-static compression experiments combined with mechanical experiments finite element simulation calculations,analysis and comparison of the deformation displacement of the rod and the maximum equivalent force cloud of the overall structure in the simulation,it is found that the heterogeneous lattice structure is similar to the lattice structure obtained from a single cell array,showing a nonlinear damage process,but due to the different cell lattice configuration,the heterogeneous lattice structure has obvious differences in ultimate strength and modulus,and by changing the different lattice cell combination mode,the new structure can be made in a different way.The compressive strength of the new structure can be increased by 243.57% and 39.715% compared with the highest of BCC and FCC,respectively;the influence of different arrangement patterns on the deformation behavior and failure of the heterogeneous lattice structure is further analyzed.The more uniformly distributed the lattice units are in the design,the closer the fracture location is to the middle of the specimen,the main failure mode is 45° angle shear failure,and the defects such as stress concentration and spheroidization are the main reasons for the collapse and fracture of the specimen. |
