Densification Behavior, Dimensional Compensation And Properties Of 316L Stainless Steel Fabricated By Binder Jet 3D Printing

Binder jet 3D printing(BJ3DP)is one of the promising techniques in additive manufacturing that employs complex structure materials with the best economy and high efficiency.However,achieving a high density of metal materials is challenging in BJ3 DP,especially obtaining higher than 99% relative density of complex structure metal materials.The sintering behavior of BJ3 DP metal materials can only be evaluated by experimental observation,especially the evolution of sintering shrinkage and densification.In addition,achieving high dimensional precision of metal materials in BJ3 DP is difficult,especially when targeting above95%-dimensional precision.In this study,more than 99% relative density of BJ3 DP 316L stainless steel(SS)was achieved by combining the regulation layer thickness to enhance green parts density with hightemperature sintering in a vacuum.The sintering behavior of 316 L SS samples manufactured by BJ3 DP was examined using the finite-element method.The model was followed a thermoelasto-viscoplastic constitutive model(FEM).The dimensional compensation technology of BJ3 DP 316L SS was developed using FEM.Finally,the immersion corrosion behavior and electrochemical corrosion behavior of BJ3 DP 316L SS and commercially rolled(CR)316L SS were compared with high relative densities(higher than 97%).The novelty of this study includes:(1)Before optimization,BJ3 DP 316L SS relative density was 95%.By combining the regulation layer thickness to enhance green component density with high-temperature sintering in vacuum technology,a relative density of 99% of BJ3 DP 316L SS was successfully manufactured.When high-temperature sintering in a vacuum reaches the supersolidus liquid phase sintering,a large volume shrinkage occurs and the intensity of densification improves.Since the relative density of green parts reaches about 53.5%,BJ3 DP 316L SS can achieve a relative density of 99% or more with the supersolidus liquid phase sintering and holding it for a long time.The results of this study provide theoretical direction for other metal materials to reach high relative density.(2)While using FEM,prediction of the shrinkage and relative density of BJ3 DP 316L SS samples during sintering can be challenging by employing the thermos-elasto elastic constitutive law.In this study,a precise quantitative simulation of the relative densities and shrinkages of BJ3 DP 316L SS samples is conducted using a subroutine(developed in Fortran and called in the FEM compiler).The subroutine was compiled considering the thermo-elastoviscoplastic constitutive law,sintering shrinkage,and densification of BJ3 DP 316L SS.The simulated results are found in good agreement with the experimental results.The sintering shrinkage and densification of BJ3 DP 316L SS are verified by the thermo-elasto–viscoplastic constitutive law.(3)After obtaining reliable results for BJ3 DP 316L SS through thermo-elasto–viscoplastic constitutive law,a dimensional compensation technology of BJ3 DP based is developed using FEM.It is estimated that dimensional compensation can produce BJ3 DP 316L SS with a dimensional precision higher than 95% as compared to ～81% dimensional precision before dimensional compensation.The dimension of the actual BJ3 DP 316L SS gear is corrected according to the compensation coefficients.The simulated results of relative density,shrinkage and dimensional precision are found in good agreement with the measured data.(4)The results show that BJ3 DP 316L SS can be developed with a density higher than99%,a dimensional precision of more than 95%,hardness of ～150 HV,the ultimate tensile strength of ～599 MPa,yield strength of ～297 MPa,and elongation to fracture of ～55%.The mechanical properties of metal injection molded 316 LSS are found compatible with ASTM B883-17.Furthermore,the corrosion resistance of BJ3 DP 316L SS is closer to CR 316 L SS,and the dominant corrosion mechanism is pit corrosion.However,the behavior of the pitting mechanism of BJ3 DP 316L SS is quite different from CR 316 L SS.It must be noted that BJ3DP316 L SS is more prone to multiple lights pitting corrosion behaviors,while CR 316 L SS exhibit local heavy pitting corrosion behaviors,this is mainly due to the difference in their microstructures and the content of alloying elements in the passive film.