Study On Gradient Cellular Structures Of 316L Stainless Steel In Selective Laser Melting

Designing bone scaffolds and implants that are consistent with the biomechanical properties of the host bone is one of the key issues in orthopedic regenerative medicine.Metallic cellular structures are suitable candidates for repairing or replacing damaged bones due to their tunable strength and porosity.However,traditional processes have only achieved limited control over the internal structure.In recent years,with recent advances in additive manufacturing,unprecedented opportunities have been provided for fabricating complex structures.At present,there are some explorations on the research of three-period minimal surface(TPMS)cellular structure fabricated by selective laser melting(SLM),but the main focus is only on the mechanical properties and specific functions of a single porosity structure,which cannot fully meet the practical application.Therefore,it is urgent to study the performance of gradient cellular structures according to the requirements of bone implants.In this paper,the optimal processing technology of 316 L stainless steel is determined by studying the influence of SLM process parameters on the forming quality of the block.Simulate the compression process of uniform cellular structure and gradient cellular structure,analyze the stress-strain variation law,and provide a basis for revealing the influence law of porosity on the mechanical properties of cellular structure.Carry out compressive mechanical performance tests of uniform and gradient cellular structures,and establish mathematical models of elastic modulus and yield strength between the two,which are used to predict the mechanical properties of gradient cellular structures.The main work content of this paper is as follows:(1)Research on quality law of selective laser melting forming.Carry out research on the effect of process parameters(laser power and scanning speed)on forming quality and grain morphology,and determine the relationship between surface quality and internal defects affected by process parameters.The results show that the forming quality,grain size and micro-morphology are influenced by process parameters.The optimization of process parameters is an effective means to improve the quality of the sample.(2)Influence study on mechanical properties of homogeneous cellular structures.Through the finite element analysis and compression test of the uniform cellular structure with different porosity,the results show that the stress concentration and strain area of the cellular structure with different porosity are the same,and their deformation characteristics are similar.The mechanical properties decrease with the increase of porosity.Due to the difference in the effective wall thickness of the unit type,the mechanical properties are different,and the mechanical properties of the Primitive structure are better than those of the Gyroid structure.The mathematical model of the unit type parameter C value,porosity p,elastic modulus and yield strength of the uniform cellular structure is established for the prediction of the mechanical properties of the uniform cellular structure.(3)A predictive model for mechanical properties of gradient cellular structures.Through the finite element analysis and compression test of the gradient cellular structure model with different gradient distribution,the results show that the stress concentration area of the gradient cellular structure is different from that of the uniform cellular structure,resulting in different deformation characteristics.In addition,the mechanical properties of the transverse gradient cellular structure are slightly higher than the uniform cellular structure,and the mechanical properties of the longitudinal gradient cellular structure are slightly lower.The relationship between the elastic modulus and yield strength of the gradient cellular structure and the uniform cellular structure is established,which is used for the prediction of the mechanical properties of the gradient cellular structures.