(Digital Presentation) Understanding Metal Additive Manufactured Surfaces

Metal additive manufacturing (AM) is being pursued as manufacturing technique in order to shorten development cycles and reduce cost through rapid iteration and agile design. Metal AM allows for designs that were not previously possible, optimizing the balance between mechanical strength and weight. However, rough as-built surfaces do not meet engineering specifications, with roughness measurements between Sa = 5 – 60 mm. Furthermore, depending on the build angle the surface roughness varies widely within a single part. These rough surfaces result in different surface morphology and chemistry compared to other manufacturing methods which has a direct impact on the susceptibility to localized corrosion and mechanical performance. This variation is also amplified depending on the machine used to build the material. We have extensively characterized the surface roughness, and corrosion response of AM 316L stainless steel (SS) that has been built on different machines which result in significantly different surface properties. Our team is also developing environmentally friendly surface finishing techniques to reduce the surface roughness to meet specifications, increase corrosion performance, and drastically reduce the part-to-part variations. We have used optical methods to measure the surface roughness of as-built AM 316L SS, A20x (AM aluminum alloy), and Ti6-4. Aqueous and atmospheric corrosion measurements have been performed on 316L SS. Finally, EDS/SEM measurements reveal there is significant chemical segregation on the surface of the as-built material; however, surface treatment methods being developed by the group have been shown to remove this layer. Post-processing surface treatments result in a more homogeneous surface and improve the performance of the material.