Materials Science Research Lecture
***Refreshments at 3:45pm in Noyes lobby
Abstract:
Additive manufacturing (AM), aka 3D printing is a relatively new technology that has given rise to the "maker culture" and an intense interest in design. That has carried over into metals AM, which has jumped almost immediately into manufacturing of actual parts in a variety of alloys. In doing so it has liberated thinking about part design albeit within certain constraints and complex components have been deployed that were previously inaccessible, e.g., high temperature heat exchangers (HX). An example is described of the co-design of HX against printing constraints, alongside evolution in alloy choice. Printed material has exhibited creep properties comparable to wrought provided that porosity is minimized. Nothing is ever as simple as it seems, however, and the reliability of parts that must carry load depends on the internal microstructure, especially with respect to extreme value properties such as fatigue loading. This motivates detailed study of all aspects of materials microstructure ranging from defect structures to strain, all of which is ideally suited to the use of intense sources of high energy x-rays as only third generation light sources can deliver. Computed tomography (CT) has revealed the presence of porosity in all additively manufactured metals examined to date and confirmed that appropriate process control can limit it. Fatigue life in stress relieved and machined Ti64 is directly anti-correlated with pore content. CT has also provided data on surface condition that explains poor fatigue performance with as-printed surfaces. High speed radiography reveals even more crucial details of how laser light generates vapor cavities that can deposit voids past a critical instability point. "Hot" cracking has been imaged as it happens during the solidification process, which offers a fresh look at how to optimize alloys for 3D printing. High speed, high resolution diffraction in stainless steel, alloy 718 and Ti-6Al-4V reveals unexpected solidification and precipitation sequences and explains why standard TTT diagrams cannot be used. Diffraction microscopy reveals the highly strained nature of printed metals and how microstructure and internal strain state evolves during subsequent annealing. Permeating all these activities is machine learning as an invaluable tool and aid to the researcher.
Support from multiple agencies is gratefully acknowledged, including NASA, DOE/BES, DOE/NNSA, ONR, NSF, OEA, Commonwealth of Pennsylvania, and Ametek.
More about the Speaker:
I have been a member of the faculty at Carnegie Mellon University since 1995. I am also the Co-Director of the NextManufacturing Center on additive manufacturing. Previously, I worked for the University of California at the Los Alamos National Laboratory. I spent nine years in management with four years as a Group Leader (and then Deputy Division Director) at Los Alamos, followed by five years as Department Head at CMU (up to 2000). I have been a Fellow of ASM since 1996, Fellow of the Institute of Physics (UK) since 2004 and Fellow of TMS since 2011. I received the Cyril Stanley Smith Award from TMS in 2014, was elected as Member of Honor by the French Metallurgical Society in 2015 and then became the US Steel Professor of Metallurgical Engineering and Materials Science in 2017. I received Cyril Stanley Smith Award from the International Conference on Recrystallization and Grain Growth in 2019. I was an International Francqui Professor (Belgium) in 2022 and I will receive the ASM Gold Medal in 2024.
My group is supported by industry and Federal agencies. My research focuses on processing-microstructure-properties relationships with interests in additive manufacturing, the measurement and prediction of microstructural evolution, the relationship between microstructure and properties, especially three-dimensional effects, texture & anisotropy and the use of synchrotron x-rays.