Gas Pore Formation in Powder Bed Fusion

Additive manufacturing (AM) of metal materials based on powder bed fusion technology is widely used now in many industries. A known limitation of this type of manufacturing is the formation of gas pores in bulk material arising from stochastic events related to molten metal fluid instabilities of a vapor depression. Here we present a combined X-ray imaging and infrared pyrometry study of pore formation in repeated adjacent tracks, and quantify the correlations of pore positions and sizes for a common material (Aluminum 6061) of interest in AM as a function of its laser processing conditions. We find in both cases that an existing pore in one track often catalyzes the formation of another pore in a consecutive track at the distance of closest approach. In a raster scan strategy commonly used to construct bulk material, this phenomenon has the result of forming perforations, or lines of pores transverse to the scanning direction in a rastered patch. If controlled, this effect can be eliminated to improve the yield strength of the build, or exploited to create programmable failures for specific purposes.<br/><br/>Distribution A. Approved for public release: distribution unlimited. (AFRL-2023-5001) Date Approved 10-10-2023.