Microscopic Characterization of Adiabatic Shear Bands in Additively Manufactured 316L Stainless Steel Hat-Shaped Specimens

The dynamic failure behavior of additive manufacturing (AM) materials is an important factor in their engineering applications. In this article, 316L stainless steel (SS316L) hat-shaped specimens along the material building direction were manufactured by a selective laser melting (SLM) machine. By carrying out split Hopkinson compression bar tests with impact bar speeds of 20m/s and 50m/s respectively, morphological characteristics of the adiabatic shear band (ASB) of the hat-shaped specimen were investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) results show that a plastic deformation band with a width of approximately 750μm is formed in the shear area of the hat-shaped specimen at an impact speed of 20m/s, and no ASB is formed. At an impact speed of 50m/s, an ASB with a width of approximately 20∼80μm was observed, and the ASB was located between a plastic deformation region and the molten pool rows. The Electron Backscatter Diffraction (EBSD) results show that there are nanoscale grains in the ASB, and a strip-like preferred orientation of grains appears in the shear region, which coincides with the molten pool rows. This may be related to the remelting mechanism. Finally, the evolution mechanism of the ASB in the SS316L hat-shaped specimen was also explained. The research provides insights into the revelation of the adiabatic shear dynamic failure mechanism of AM materials, the prediction of dynamic instability behavior of AM materials, and even the failure modes of customized AM materials.