The Dynamic Failure Behavior Of Additively Manufactured 316L Stainless Steel At High Strain Rate

Laser additive manufacturing technology is one of the most innovative metal material manufacturing processes currently.Compared with traditional manufacturing processes,the layer-by-layer processing method of additive manufacturing technology has many advantages,such as ultra-high design freedom,near-zero material waste,and a shorter molding cycle.Therefore,laser additive manufacturing is considered to be a disruptive advanced manufacturing technology with broad application prospects in aerospace,transportation,safety protection,and other fields.However,few studies to date have delved into the mechanical properties and failure behavior of laser additively manufactured metals under high-speed shock.This paper systematically studies the dynamic mechanical properties,failure behavior,and microstructural evolution of additively manufactured(AM)316L stainless steel.The main research contents include:(1)Based on the Split Hopkinson Pressure Bar(SHPB)technology,a high strain rate dynamic shock compression shear experiment of AM 316 L stainless steel was carried out.The mechanical properties of AM 316 L under dynamic conditions such as ductility,strain hardening,yield to failure,and strain rate effects are analyzed.The AM 316 L exhibits strain rate insensitivity and the relative brittleness of the material compared to the wrought 316 L.(2)The deformation failure of AM 316 L stainless steel under dynamic shock compression shearing is observed based on metallographic microscope technology,and fracture failure,adiabatic shear band failure,and local plastic deformation failure are studied.AM 316 L exhibits distinctly discontinuous adiabatic shear band propagation.The plastic torsional deformation process of the molten pool blocks the propagation of cracks between the molten pools formed by different laser tracks.The characteristic molten pool structure of deposition molding affects the deformation failure characteristics,and the microscopic mechanism during the failure process will affect the dynamic mechanical properties of the AM 316 L.(3)Based on Electron Back-scattering Patterns(EBSD)technology,the initial grain morphology and distribution of AM 316 L stainless steel molten pool deposition molding are characterized.The local crystal morphology and microstructural evolution under the adiabatic shear band and local plastic deformation failures are characterized in multi-scale.The extremely high initial forming dislocation density and small grain size allow the AM 316 L to achieve a high yield strength of the material,but make the material more brittle.The columnar crystal structure radially distributed with the laser focus deposited with the molten pool is stretched along the shear direction under dynamic impact.The microscopic features of molten pool deposition affect the dislocation motion of the material and the hardening and softening of the material during plastic deformation.(4)Through the calculation of grain orientation deviation,lattice curvature tensor,and local dislocation density tensor based on EBSD technology,the changes in grain orientation difference and dislocation density during dynamic plastic deformation are quantitatively analyzed.The grain misorientation has a distinct step at the molten pool boundary.The dislocation density after dynamic failure did not increase significantly.The grain misorientation becomes larger in the local grain boundaries while the distribution value of the overall grain boundary does not increase significantly.These partly explain the strain rate insensitivity of AM 316 L stainless steel.In the process of plastic deformation,the shear stress drives the rotation and slip of the grains.The grains tend to rotate asymptotically in a stable direction,and the crystal slip is deflected by the Schmidt factor.In summary,this paper systematically studies the dynamic mechanical behavior of AM 316 L stainless steel,and innovatively quantitatively analyzes the microstructure evolution process under adiabatic shear band failure and local plastic deformation failure.A link between the microstructural features and dynamic mechanical properties under dynamic failure behavior is established.It provides a theoretical basis for revealing the dynamic mechanical behavior of advanced manufacturing metal materials and provides scientific guidance for expanding the application of additive manufacturing materials in the dynamic impact field.