Laser Directed Energy Deposition of Bulk 316L Stainless Steel

Abstract

Laser directed energy deposition (DED) of high-density parallelepiped 316L stainless steel specimens has been performed while varying laser power, scanning velocity, powder mass flow rate and layer thickness. An extensive set of analyses has been performed into the resulting dimensions, surface roughness, microstructure, hardness, tensile strength, build substrate temperature, deposition efficiency, production time and specific energy input with the aim of differentiating variations in component performance and process efficiency for components that have already been optimized in terms of density. Average layer height is found to be an approximately linear function of the powder line mass flow rate, while samples with the same powder feed per unit length have similar microstructures despite differences in scanning velocity and total powder feed rate. The hardness of specimens is generally higher than bulk 316L stainless steel, while yield and ultimate tensile strength are similar or higher than the bulk material but with dependence on the load direction. Deposition efficiency is strongly influenced by the scanning strategy and laser off time, with values as low as 42% with a “raster” scanning strategy and up to 84% with a “snake” scanning strategy. The large number of analyses performed on high-density components provides important new insight into factors affecting build quality and process efficiency that go beyond simply maximizing density, suggesting that significant further improvements can be obtained. Such knowledge is exploitable for application-specific process optimization and implementation of open and closed-loop height control strategies for production of bulk 316L stainless steel components.