November 2023 Volume 5

FORGING RESEARCH

Using Bright X-Ray Beams To Look Inside Alloy Processing By Darren C. Pagan and Lukas A. Kissell

Lab X-ray diffraction is an important tool for non-destructively characterizing the microstructure and residual stress state of manufactured alloy products. By measuring the positions and intensity of scattered X-rays from a sample, the crystal structure, orientation, and stress are determined, which can be critical information for optimizing manufacturing processes and final products. A limitation to these measurements is that they are generally confined to the surface of a sample, as the low-energy X-rays generated in a lab cannot penetrate an alloy, and relatively dim laboratory sources lead to long collection times, limiting the number of measurements that can be made. To address these issues, the past two decades have seen a major proliferation of the use of synchrotron X-ray sources for the study of alloy structure, processing, and performance. Synchrotrons are particle accelerators originally designed for high-energy physics, but a by-product of particle acceleration, X-rays, have become an indispensable tool for materials science and engineering. If a laboratory source has the brightness of a candle, a synchrotron has the brightness of the lights of a football stadium. The bright X-ray beams from synchrotrons are now allowing researchers and engineers to directly watch movies of mechanisms that have been previously hidden during both processing simulation and performance testing. With these measurements, new insights are being gained about both old (e.g., understanding the origins of fatigue failure) and new (e.g., controlling microstructure during additive manufacturing) metal alloy challenges. Despite the impact that these new measurements are having on many aspects of metal alloy research, to date, they have not been extended to probing critical industrial manufacturing processes such as forging. The challenge lies in recreating the complex thermomechanical conditions encountered during manufacturing, while still allowing an X-ray beam to enter and exit the sample chamber. For example, forging shapes an alloy with multiaxial distortional stresses, often at high temperatures and pressures. A recent FIERF microgrant supported developing new synchrotron compatible measurement capabilities for studying industrial manufacturing, including forging, at Penn State and the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory with the aim of using synchrotron measurements to accelerate industrial process design.

Figure 1: A synchrotron-compatible multi-anvil assembly which can mimic conditions found during industrial processing while allowing an X-ray beam to probe material evolution. To make this possible, inspiration was taken from the geological community. To recreate and study the flow of rocks in the Earth’s mantle, synchrotron-compatible multi-anvil hydraulic presses have been developed that allow for application of multiaxial loads at high temperatures (500 to 2000 °C) to relatively large samples containing tens of thousands to millions of individual crystals. A schematic of an example anvil system is provided. While at a glance,

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