316L steel  – surfaces oxides – no bulk oxides
New powder particles:
Single fcc austenitic phase, alloying elements in full solid solution with no intergranular precipitates (characteristic of rapid cooling rate during gas atomisation)
coarse microstructure with mainly equiaxed grains, grain boundary segregation Cr, Mo, and Mn – coarser grain + segregation: slower cooling rate?
Surface of spatter particles:
preferential Mn + Si oxides,
AlSi10Mg  – surface oxides – no bulk oxides
non homogeneous: outer shell with core, no intermetallic compounds (Mg2Si), Si-rich areas in the core,
larger than particle, homogeneous structure, no intermetallic compounds distinguishable, no oxide in the bulk, surface Mg-rich oxides,
Ti64  - no surface or bulk oxides
compositional analysis (EDS) shows all elements in full solid solution, no surface oxides
- Regardless of the material, condensate particles are larger than the starting pre-alloyed powders with a spherical morphology.
- Selective oxidation occurs at the surface of the condensate particles of 316L and Al-Si10-Mg.
- No oxides were observed in the bulk microstructure of the spatter particles.
- The analysis suggests that the formation of surface oxides is underpinned by surface enrichment of the most volatile element present in the alloy. If these elements also have great affinity to oxygen, as in the case of Mn, Si, and Mg, thick oxides layers (up to several um) can be formed.
- The laser spatter formed during the processing of Ti-6Al-4V contains no oxides, likely because the alloy has no alloying elements with high volatility.
- Promoting efficient conduction melting will decrease oxidation occurring and spatter(waste).
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8 MARCO SIMONELLI, CHRIS TUCK, NESMA T. ABOULKHAIR, IAN MASKERY, IAN ASHCROFT, RICKY D. WILDMAN, and RICHARD HAGUE, A Study on the Laser Spatter and the Oxidation Reactions During Selective Laser Melting of 316L Stainless Steel, Al-Si10-Mg, and Ti-6Al-4V, METALLURGICAL AND MATERIALS TRANSACTIONS A DOI: 10.1007/s11661-015-2882-8