Texture and damage evolution in additively manufactured 18 %Ni-M350 maraging steel under dynamic impact loading: Processing parameters and heat treatment effects

Abstract

The mechanical and microstructural responses of 18 % Ni M350 maraging steel produced by additive manufacturing (AM) using the direct energy deposition (DED) laser process under impact loading are investigated. The material is manufactured using low and high energy area density (EAD) to identify the influence of AM processing parameters on the impact strength, microstructural, and texture evolution during deformation. In addition to the as-built (AB) state, maraging steel samples subjected to solutionizing and aging heat treatment (HT) are also investigated. Electron backscatter diffraction (EBSD) is used to characterize texture evolution under impact loading. The test results reveal that the low-EAD material exhibits the greatest impact strength for the applied strain rates that ranged from 200 to 3300 s−1 in its as-built state. This finding is attributed to the high local misorientation that is closely correlated with the dense dislocation network generated as a result of the rapid cooling process. The activation of a new slip systems {112}〈111¯〉 and {123}〈111¯〉 is observed after deformation at high strain rates in the as-built material. A higher degree of new slip system activation in low-EAD samples suggests a higher susceptibility to the initiation of an adiabatic shear band (ASB). The effects of processing parameters on impact strength, strain, and propensity to defects are eliminated by heat treatment. The improvement in impact strength of the steel materials after heat treatment can be attributed to the dominance of precipitate-dislocation interactions as the primary strengthening mechanism. Furthermore, heat-treated materials exhibit the highest susceptibility to deformation-induced defects, such as adiabatic shear bands and fracture.