Meaning
Internal voids filled with inert gas represent a persistent class of material defect in metal powders and consolidated parts produced by powder bed fusion. When metal is atomized using inert gas, argon porosity arises as gas becomes trapped within the solidifying droplets. These microscopic pockets persist through subsequent laser processing because the inert gas does not dissolve into the solid metal matrix.
Sourcing decisions for critical aerospace components often depend on verifying that powder feedstock has minimal internal gas content.
Entrapment Process
High pressure gas jets break up the molten metal stream during the atomization stage of powder production. Turbulent flow during this breakup causes a portion of the atomizing medium to become enclosed in the molten droplets. Once enclosed, the gas cannot escape before the droplet freezes.
This mechanism locks the gas inside the finished powder particles.
Analysis Technique
Pycnometry measures the density of the powder to reveal the presence of internal voids. Powder samples are weighed and then evaluated using helium displacement to find the apparent volume. Comparing this value to the theoretical density of the alloy gives a measure of the closed void space.
X-ray computed tomography provides a detailed spatial view of the internal voids.
Industrial Consequence
During the consolidation process, these gas pockets remain in the build and can cause microstructural failures. The pocket behaves as a stress concentrator during cyclic loading. Mechanical failure begins at these sites.
