Abstract
This study evaluates the elevated temperature mechanical performance of 316H stainless steel produced using directed energy deposition (DED) additive manufacturing (AM) from three separate collaborative research programs focused on understanding how AM variables affect creep performance. By combining these studies, a critical assessment of variables was possible including the DED AM method (laser powder and gas metal arc wire), laser power, sample orientation relative to build orientation, chemical composition, and post-processing heat treatment. Detailed microstructure characterization was used to supplement creep and chemistry results to provide insights into potential mechanistic differences in behavior. The study found that sample orientation was a critical variable in determining lower-bound creep behavior, but that in general the lowest creep strength orientation and the lowest creep ductility orientation were not the same. Heat treatment was also an important variable with as-printed materials showing for specific test conditions improved performance and that underlying substructures formed due to inhomogeneous chemical distributions were not completely removed when using standard wrought solution annealing heat-treatments. The chemistry of the final deposited parts differed from the starting stock and may be an important consideration for long-term performance which is not fully appreciated. Overall, the study found that while all the DED materials tested fell within an expected wrought scatter band of performance, the actual creep performance could vary by an order of magnitude due to the many factors described.
