Defect Types and Formation Mechanism of Fe-Mn-Cr-Ni Medium Entropy Alloys Formed via Selective Laser Melting
In this study,a Fe-Mn-Cr-Ni medium entropy alloy is fabricated using selective laser melting.By varying the laser power and scanning speed,the surface imperfections and quality of the alloy samples with different energy density are evaluated.The result shows that as the bulk energy density increases,the relative density of the samples initially increases and then decreases,whereas the surface roughness initially decreases and then increases.Under a low bulk energy density(≤77.38 J/mm3),the powder on the alloy surface is sintered together owing to insufficient melting,thus resulting in a protruded surface.The main internal defects are spheroidization defects caused by powder non-fusion.Under a high bulk energy density(≥104.76 J/mm3),the droplets generate during the forming process splash and accumulate on the surface of the sample,thus causing a keyhole effect within the alloy and inducing microcracks.The hardness of the formed block first increases and then decreases as the bulk energy density increases.The sample with a bulk energy density of 88.44 J/mm3 exhibits the highest relative density(99.5%)and superior forming quality.Additionally,it exhibits as Vickers hardness of 211 HV,a tensile strength of 549 MPa,and an elongation of 21.8%.
medium entropy alloyselective laser meltingvolume energy densitydensityforming defect
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