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Effects of Thermal History and Isostatic Pressing on the Microstructure Evolution of Metallic Components Manufactured by Selective Laser Melting (SLM)
R-D. Li, T-C. Yuan, Q-S. Wei, L. Wang and Y-S. Shi

The influences of thermal history and isostatic pressing on the microstructure evolution of a selective laser melting (SLM) component were studied in this paper. It showed that with the increase of line energy density from 1.1 to 1.9 J/mm, the as received grain size tended to coarsen from 0.7 to 1.2 μm, due to the longer thermal duration. The layer thickness also had an appreciable effect on the microstructure evolution. With the increase of layer thickness from 0.05 to 0.5 mm, the grain size coarsened from not more than 1 μm and 3 to 5 μm, because of the lower heat conductivity of powder and resultant longer solidification duration at a thicker layer thickness. The cantilever structure of SLM part also had a great influence on the microstructure evolution. In the inner of SLM part with a cantilever structure, the grain size of the cantilever zone was larger than that in the non-cantilever zone. In the lower limb of SLM part with a cantilever structure, with the gradual increase on the sloped angle, the microstructure evolved from cellular, to dendrite, then isometric in sequence. Hot isostatic pressing (HIP) technology, as a post-treatment route of SLM, could enable the crystal growth from about 1 μm to 20 to 100 μm, accompanied with many substructures with triangle shapes.

Keywords: Selective laser melting (SLM), microstructure evolution, thermal history, isostatic pressing, line energy density, layer thickness, cantilever structure

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