On Porosity and Its Mitigation and Closure in Additively Manufactured Alloys

Porosity has long been observed in manufacturing metal alloys, which is much more frequent in additively manufactured (AM) alloys than in those manufactured by traditional methods such as cast and wrought. The common origin of porosity is strongly depending on specific manufacturing process parameters and conditions. In general, pore structures can originate from a variety of factors, including trapped gas, incomplete fusion, cooling rate, feedstock quality, processing parameters and conditions, etc. By carefully controlling the manufacturing process and conditions, the porosity in AM-alloys can be mitigated. Besides, post-AM treatment, e.g., hot isostatic pressing and/or cold working, can reduce the porosity (in both the size and density) through plastic deformation and materials flow. Here, we present a glimpse on porosity and its effect on mechanical performance of AM alloys. Mitigation and closure of porous structures will also be discussed mainly based on recent observations in aluminum- and nickel-based AM alloys, representing high-temperature high-strength and low-density applications, respectively.