Microstructure and properties of parts manufactured by directed energy deposition of water-atomized low-alloy steel powders

Abstract

Abstract The feasibility of using water-atomized low-alloy steel powders [Fe-0.11C-0.59Mn-0.43Si-0.45Cu-0.3Cr-0.45Ni-0.15Mo-0.05 V (wt.%)] for additive manufacturing using a laser-based directed energy deposition (DED) process was evaluated. Different processing parameter combinations were assessed to arrive at optimum parameters to fabricate different sample geometries, which were characterized in terms of microstructures and mechanical properties. Selected samples were also evaluated after homogenization at 1075 °C for 10 min. The results show that DED of water-atomized low-alloy steel powders is possible, yielding unique non-directional and refined microstructures with fine spherical oxide particles dispersed throughout the matrix. The maximum tensile strength and total elongation achieved in the as-built condition were 315 MPa and 3.4%, respectively, which improved to 350 MPa and 10.3% after heat treatment. The presence of a sizeable fraction of oxide nanoparticles, which presumably originated from the oxide layer of the water-atomized powder, enabled retention of microhardness/strength after heat treatment despite grain coarsening. However, the porosity and loss of C and Mn were found to be the major concerns with water-atomized powder. We believe that inconsistent powder flow due to the irregular morphology of the powders is the primary cause of the porosity. On the other hand, the high laser absorptivity of the powders due to their rough surface texture and surface oxides could be responsible for the loss of alloying elements due to excessive powder and/or melt pool temperatures. Although the results of our study are quite encouraging, powder characteristics like size and/or morphology need to be further optimized to exploit the full potential of this additive manufacturing methodology.