IMX Talks - Microstructures and mechanical properties of additively manufactured alloys

A detailed understanding of the correlations between the processing, microstructures, and mechanical performance of alloys is a must before they can be deployed for structural applications that demand a high degree of reliability. Such an understanding, which allows for tailoring of advanced alloys for the targeted performances, is well-established for those manufactured using the conventional (CM) routes, which offer several options for tuning the microstructures. However, some of them—especially microstructural tuning through the judicious selection of the thermo-mechanical processing steps—are not available for additively manufactured (AM) metallic components. Alloys made with AM techniques such as laser powder bed fusion (LPBF) have substantially finer microstructures (due to rapid solidification) and distinct mesoscale features. Consequently, their strength is often higher while the ductility is lower, vis-à-vis their CM counterparts. The meso-structural features, a result of the ‘bottom up’ approach of building components—line-by-line and layer-by-layer with in-situ alloying capability—can impart very high fracture toughness to these alloys. The presence of porosity, which is inevitable given that the feedstock is often powder, results in lowered unnotched fatigue resistance. Implications of these in terms of possible directions for designing AM alloys with high mechanical performance will be discussed.

Bio: After obtaining a PhD degree from Brown University under the supervision of Professor Subra Suresh and post-doctoral stints at UCSB and MIT, Ramamurty held faculty positions at the Nanyang Technological University, Singapore and the Indian Institute of Science, Bangalore, India, before returning to NTU in 2018 where he currently holds a President's Chair Professor position. His research interests include deformation and fracture behavior of amorphous as well as crystalline alloys, additive manufacturing, and the development and application of the nanoindentation technique. He is an editor of Acta Materialia and Scripta Materialia, and a Fellow of the Indian National Science Academy, Indian National Academy of Engineering, and TWAS-The World Academy of Sciences.