Understanding the events that take place during metal melting and resolidification is a key success factor of metal SLM technology. Investigation into spatter generation reveals that surface oxides enriched in the most volatile alloying elements of the material are present in the residue.
Research shows that the melting regime and the melt pool stability depend on the presence of oxides that might form during SLM. Considering the O2 partial pressure present in SLM build chambers, it is likely that the high temperatures reached by the melt pool could trigger the formation of oxide films.
Thin (nm range) protective oxide layers found on metals such as stainless steel and titanium alloys, can be stirred by the melt pool dynamics  and may have a negligible effect on the SLM production. However, the process may not completely disrupt or vaporise thicker oxides layers. These oxide residues tend to lower wetting ability, induce balling and deteriorate the melt pool stability .
For typical energy inputs used in SLM (10E5 to 10E7 W/cm2), some metallic compounds may evaporate to a certain extent [1,3]. Little has been studied on material evaporation during SLM, but research on laser welding reports that the evaporation affects laser absorption, giving rise to the re-deposition of fumes inside the building chamber and contributes to the ejection of laser spatter from the melt pool.[4–7]
As it originates directly from the melt pool, spatter can provide important information regarding the oxidation reactions that occur during SLM. Here we summarise findings for three widely used materials.
316L steel  – surfaces oxides – no bulk oxides
AlSi10Mg  – surface oxides – no bulk oxides
Ti64  - no surface or bulk oxides
New and spatter particles:
compositional analysis (EDS) shows all elements in full solid solution, no surface oxides
The compositional analysis of the oxides found on the laser spatter shows selective oxidation of mainly Mn (and Si) in 316L stainless steel and Mg in Al-Si10-Mg.
1. S. Das: Adv. Eng. Mater., 2003, vol. 5, pp. 701–11.
2. E. Louvis, P. Fox, and C.J. Sutcliffe: J. Mater. Process. Technol., 2011, vol. 211, pp. 275–84.
3. F. Verhaeghe, T. Craeghs, J. Heulens, and L. Pandelaers: Acta Mater., 2009, vol. 57, pp. 6006–12.
4. M.J. Zhang, G.Y. Chen, Y. Zhou, S.C. Li, and H. Deng: Appl. Surf. Sci., 2013, vol. 280, pp. 868–75.
5. D.K. Low, L. Li, and P. Byrd: J. Mater. Process. Technol., 2003, vol. 139, pp. 71–76.
6. S. Li, G. Chen, S. Katayama, and Y. Zhang: Appl. Surf. Sci., 2014,vol. 303, pp. 481–88.
7. A.F.H. Kaplan and J. Powell: J. Laser Appl., 2011, vol. 23, pp. 1–8.
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
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