Atmospheres for laser powder bed fusion

Camille Pauzon¹, Pierre Forêt², Eduard Hryha¹

¹Chalmers University of Technology, Sweden, ²Linde GmbH, Unterschleissheim, Germany

Laser powder bed fusion has lately gone through important advances promoting its industrial adoption, such as the development of in situ monitoring systems. The present work will introduce some results enabled by this progress, connected to the effect of the process atmosphere on the stability of the generated melt pool and the properties of the built materials, for example with the use of atmosphere purity monitoring, process imaging, high resolution microscopy.  
Until recently, the role of the process atmosphere, which is traditionally established using inert argon gas, has been limited to reduce the oxygen content present in the process chamber from air level (21%) down to a typical threshold of 1000 ppm O2, with the aim to reduce the possible oxidation of the exposed material. 
The influence of residual impurities such as oxygen and nitrogen on the degradation of 316L stainless steel, Alloy 718 and Ti-6Al-4V powders exposed to the AM environment will be presented, as well as the associated properties of the as-built materials. Finally, insights on the beneficial use of addition of helium to the process gas to reduce spatter generation will be demonstrated.