The field of materials science has received significantly more attention in the previous decade with the growing recognition that many innovations require new materials to make them a reality. The continued exponential growth of computing capacity has led to the burgeoning field of computational materials science – perhaps best exemplified by the Materials Genome Project – where new materials can be discovered using materials property data, thermodynamics, and the fundamental principles of chemistry and physics. However, in order for calculations to be accurate, the models employed must be reliable. As Dr. Christopher Hefferan and his colleagues at Carnegie Mellon University working under the direction of Professors Robert Suter and Gregory Rohrer discovered, even long-standing models of microstructural development of engineering alloys may not describe material behavior in important ways.
The microstructure of metal alloys is composed of grains – the fundamental building block of the material. A host of processing conditions – including composition, temperature, and deformation – determine the size and shape of the grains that exist in any metallic part. In turn, the grain size will control the mechanical properties of the alloy, including strength and toughness. Computational material science can model entire alloys that have never been made yet can predict the microstructure of that material – in part based on the previous “knowledge” that the velocity of a grain boundary is related to the curvature of that boundary. Knowing which grain boundaries will move faster than others as the material is heated or cooled or deformed is necessary to know whether a metal will be composed of a single grain, millions of tiny grains, or somewhere in between.
Using the Advanced Photon Source’s synchrotron radiation light source at Argonne National Laboratory, Dr. Hefferan conducted a series of experiments that tracked a macroscopic nickel polycrystal (many grains) through a series of heating steps. Here, the individual evolution of thousands of grains were monitored as they were exposed to incremental stimulation through annealing — a fundamental heat treatment that occurs in many processes necessary to make finished parts from metal alloys. The results demonstrated that while many theoretical models suggest grain boundary velocity and curvature are directly correlated, these are not the only driving forces that dictate microstructural development. Notably, the network formed by the connected grain boundary skeleton also influences this evolution.
While he graduated from Carnegie Mellon University in 2012, Dr. Hefferan’s work formed the experimental basis for the paper just published in Science “Grain boundary velocity and curvature are not correlated in Ni polycrystals” (Bhattacharya et al., Science 374, 189–193 (2021) 8 October 2021) of which he was co-author.
Dr. Christopher Hefferan is a Senior Consulting Scientist and has been employed by RJ Lee Group since 2012; the Company congratulates him on this significant scientific accomplishment.
This work was supported by the National Science Foundation under grant DMR 1628994 to Gregory Rohrer and Robert Suter of Carnegie Mellon University. The Advanced Photon Source is a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357 (to Robert Suter of Carnegie Mellon University).
The Science family of journals is published by the American Association for the Advancement of Science (AAAS), the world’s oldest and largest general science organization. The nonprofit AAAS serves 10 million people through primary memberships and affiliations with some 262 scientific societies and academies.