Study On The Influence Of SLM Process Parameters On The Microstructure,Performance And Deformation Mechanism Of AISI 316L

Selective Laser Melting（SLM）is one of the commonly used additive manufacturing methods.It has obvious advantages for metal parts that are difficult to directly produce with traditional processing technology,small batches,and individual needs.In this paper,AISI316L stainless steel is prepared by the SLM method,and the process parameters are optimized by analyzing single-layer single-pass,single-layer multi-pass and bulk samples under different process parameters.and the process parameters were optimized.The microstructure,composition characteristics,mechanical properties,and deformation behavior of the sample under the optimized process parameters of AISI 316L stainless steel prepared by SLM method are systematically studied.When the laser power is constant,the depth and width of the molten pool decrease with the increase of the scanning speed.When the scanning speed is constant,the depth of the molten pool increases with the increase of the laser power,and the width of the molten pool does not change significantly.Increasing the laser power or decreasing the scanning speed will increase the melt channel height.But when the laser power is too large and the scanning speed is too small,the solution in the molten pool will splash and reduce the height of the molten channel.If the scanning distance is too small,the height of the adjacent melt channel is gradually increasing.If the scanning distance is too large,the surface of the melt channel will be uneven.When the overlap ratio ranges from 27%to 38%and the laser energy density ranges from 83 to 104 J/mm³,the quality of the formed layer is better.When the overlap ratio is 33.67%,the sample has the highest density with a value of 98.68%.The optimized process parameters are:the laser power is 250 W,the scanning speed is 1200 mm·s^-1,and the scanning distance is 80μm.The block sample adopts the Cross-hatching scanning strategy and is printed along the positive z-axis.Therefore,the microstructure of the xz plane and the yz plane are similar.The AISI 316L stainless steel prepared by the SLM method has a single-phase austenite structure,which has a large number of hexagonal,elongated hexagonal cell structures and bar-columnar substructures.Most of the crystal grains in the xy plane grow along the（220）crystal plane preferential orientation,and the majority of the crystal grains in the yz plane preferentially grow along the（111）crystal plane.In addition,columnar crystals with（111）orientation in the yz plane may be epitaxially grown through one or more fusion lines.The roughness of the xy plane is Rz=23.0μm,Ra=2.12μm,and the roughness of the yz plane is Rz=32.43μm,Ra=4.33μm.The Brinell hardness of the xy plane is 178.66 HB,and the Brinell hardness of the yz plane is 187.62 HB.The tensile strength of the sample is696.73 MPa,the yield strength is 571.37 MPa,the elongation is 52.59%,and the yield ratio is 0.82.There are a large number of dimples with sizes ranging from 100 to 600 nm and pores ranging from 8 to 70μm in the tensile fracture.Nano-scale dimples increase the deformation energy required in the fracture process,thus delaying fracture and improving plasticity.When the strain amount of the sample reaches 30%,the deformation twinΣ3 grain boundary increases significantly.When the strain amount reaches 52.59%,theΣ3 grain boundary reaches 35.3%at most.When the grain orientation is close to<111>or<110>,the grain size is larger,and deformation twins are prone to occur.When the orientation is close to<001>,the grain size is smaller and deformation twins are not prone to occur.As the amount of strain increases,the average density of Geometrically Necessary Dislocation（GND）increases from 3.63×10¹⁴ m^-2 to 8.17×1014 m^-2.GND increases dislocation resistance through dislocation interaction and back stress,thereby increasing the yield strength of the material.As the amount of strain increases,both dislocation slip and twinning increase.The two coordinate with each other,therefore,the AISI 316L stainless steel prepared by the SLM method has high strength and good plasticity.