Abstract
This study analyzes the local deformation behavior of austenitic stainless steel 316L, manufactured conventionally by casting and additively by laser metal deposition (LMD). We produced directionally solidified 316L specimens with most grains showing (001) orientations parallel to the longitudinal specimen axis. We conducted nanoindentation and scratch experiments for local mechanical characterization and topography measurements (atomic force microscopy and confocal laser scanning microscopy) of indentation imprints and residual scratch grooves for the analysis of the deformation behavior and, in particular, of the pile-up behavior. The local mechanical properties and deformation behavior were correlated to the local microstructure investigated by scanning electron microscopy with energy dispersive X-ray spectroscopy and electron backscatter diffraction analysis. The results show that the local mechanical properties, deformation behavior, and scratch resistance strongly depend on the crystallographic orientation. Nearly (001)-oriented grains parallel to the surface show the lowest hardness, followed by an increasing hardness of nearly (101)- and (111)-oriented grains. Consequently, scratch depth is the greatest for nearly (001)-oriented grains followed by (101) and (111) orientations. This tendency is seen independently of the analyzed manufacturing route, namely Bridgman solidification and laser metal deposition. In general, the laser metal deposition process leads to a higher strength and hardness, which is mainly attributed to a higher dislocation density. Under the investigated loading conditions, the cellular segregation substructure is not found to significantly and directly change the local deformation behavior during indentation and scratch testing.
Highlights
Due to the possibility of creating near-net shape components on demand, laser-based layer-by-layer densification of metallic powders by means of additive manufacturing is being increasingly used in a broad range of industrial applications
We have focused on local mechanical behavior during scratch and indentation testing of additively-manufactured (LMD) 316L microstructures, in comparison to conventionally cast, hot-rolled, and solution-annealed, as well as directionally solidified, 316L microstructures
We investigated the local mechanical behavior during scratch andscale indentation h* of the Nix-Gao model
Summary
Due to the possibility of creating near-net shape components on demand, laser-based layer-by-layer densification of metallic powders by means of additive manufacturing is being increasingly used in a broad range of industrial applications. A metal powder is fed by a nozzle and an argon gas jet into the local laser weld bath on the component to be produced. This process enables local buildup of a component by the systematic movement of the laser. There is a process-dependent repetitive remelting and reheating of already solidified structures with overlapping heat-affected zones. This leads to unique microstructures solidified away from thermodynamic equilibrium, with high residual stresses that are highly dependent on the processing parameters and the building direction. These microstructures have a higher hardness and strength than conventional microstructures [8]
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