Additive manufacturing (AM) has received significant attention in recent years because of its potential to transform the commercial production of components, particularly for high-value, low-volume applications, where part geometries and other requirements make them difficult or impossible to produce via conventional processing methods. One inherent drawback to current AM technology is the reproducibility of microstructures and properties of materials created via the additive process. This is because most of the alloys currently in use for AM applications were originally developed for dramatically different processing routes, namely conventional cast and/or wrought processes. Thus, the microstructures and properties of alloys built using AM processes can be dramatically different than nominally identical wrought counterparts. In many cases, properties also show significant variation from build to build using the same AM process, making component design using such materials impossible. In the present work, we investigate the processing-structure-relationships in additively manufactured materials, focusing on thermal processing in the solid state, i.e. post-built material. Specifically, Inconel 625 and 17-4 PH stainless steel are investigated. As expected, as-built microstructures are comparable to welded materials, and they respond in a similar manner to thermal processing as welded alloys. However, differences are also observed, resulting from the unique processing history of AM alloys compared to conventional materials. For example, composition differences arising from the gas atomization of powder feedstock. Using both computational modeling and experimental investigation the differences in microstructural evolution behavior of conventional and AM materials are highlighted; and post-build thermal processing regimens are identified to develop more uniform predictable AM-produced microstructures. Finally, the future of AM will also be discussed, where the dream is to employ alloys specifically designed to take advantage of AM processing instead of repurposing alloys designed for other applications. Some possible considerations for AM alloy design will be discussed.
Dr. Eric A. Lass is an Assistant Professor at the University of Tennessee, Knoxville. He received a B.S. in Materials Science & Engineering from Michigan Technological University in 2001, an M.S. in Materials Engineering from Rensselaer Polytechnic Institute in 2003, and a Ph.D. in Materials Science and Engineering in 2008 from the University of Virginia. Before arriving in Knoxville, Dr. Lass spent 10 years at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. Dr. Lass’ research interests are in process-structure-property relationships, specifically the application of thermodynamics and kinetics to microstructural evolution and phase transformations in metals and alloys, and in understanding how microstructural evolution can be controlled to enable the design of new materials and processes. His current projects include additive manufacturing of Fe-, Ni-, Co-, and Al-based alloys, microstructural evolution in high performances alloys like Ni- and Co-based superalloys and complex concentrated alloys (a.k.a., high-entropy alloys), and Integrated Computational Materials Engineering (ICME) assisted materials design.