MSE Colloquium: Dr. Anthony Rollett, 3D Printing, Porosity, Synchrotron Experiments, and Machine Learning

U.S. Steel Professor of Metallurgical Engineering and Materials Science, Dept. of Materials Science & Engineering, Carnegie Mellon Univ.

Abstract

3D printing of metals has advanced rapidly in the past decade and is used across a wide range of industry. Many aspects of the technology are considered to be well understood in the sense that machines make parts and temperature histories with residual stress can be simulated. At the microscopic scale, however, more work is required to quantify, understand and predict defect- and micro-structures, which affect properties such as fatigue resistance. The most dramatic synchrotron-based technique is dynamic x-ray radiography (DXR) which provides ultra-high speed imaging of laser melting of metals and their powders. This has, e.g., enabled the keyhole phenomenon to be quantified, which in turn has demonstrated the importance of power density, as opposed to energy density. This latter quantity, while informative, also fails to capture the crucial boundary between full density and lack-of fusion porosity because it does not take account of melt pool overlap. Synchrotron-based 3D X-ray computed microtomography (µXCT) showed that essentially all metal powders exhibit porosity that partially persists into the printed metal. This explanation is reinforced by evidence both DXR and simulation. To illustrate the power of machine learning, Computer vision (CV) has successfully classified different microstructures, including powders. The power of CV is further demonstrated by its ability to detect and classify defects in the spreading of powder. High speed synchrotron x-ray diffraction is beginning to provide new information on solidification and phase transformation in, e.g., IN718, Ti-6Al-4V and stainless steel. High Energy (x-ray) Diffraction Microscopy (HEDM) experiments also is also providing data on 3D microstructure and local elastic strain in 3D printed materials such as Ti-6Al-4V and stainless steel.

Bio

 

Research group website

I have been a member of the faculty at Carnegie Mellon University since 1995. I am also the Co-Director of the newly formed 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 was chosen to be a Fellow of TMS in 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 and also the International Francqui Professor for 2019-2020, from the Francqui Foundation, Belgium. My research group is supported by AFOSR, DOE/BES, DOE/EERE, DOE/ARPA-E, NASA, PITA, NSF, Boeing, NextM and Northrop-Grumman. The focus of my research is on additive manufacturing, the measurement and prediction of microstructural evolution, the relationship between microstructure and properties, with a particular emphasis on three-dimensional effects, texture & anisotropy and the use of synchrotron x-rays.