Microstructure evolution of 316L produced by HP-SLM (high power selective laser melting)

Abstract

New generation of selective Laser Melting (SLM) machines are evolving towards higher power lasers as well as multi laser systems in order to increase the productivity. The increase in laser power and the modification of the laser power distribution leads to microstructural and mechanical property variations that are still not well understood.This work aims at better understanding the interaction of a 1 kW top-hat power distribution laser on a well know material, 316 L stainless steel. The influence of texture and microstructure on relative density and crack density, when varying scan rotation, was evaluated. The high power (HP) laser and low power (LP) laser were compared with respect to microstructure and mechanical properties. HP leads to an increase in morphological and crystallographic texture together with a coarsening of the cell structure in contrast to the more random and finer cells found in LP processed material. Hot isostatic pressing was applied as a post-process treatment in order to close remaining pores and cracks. This helped in achieving higher elongations for LP and HP processed materials, while competitive mechanical properties to the 316 L material specifications were obtained in both cases.