PNNL

Abstract

High speed shear deformation is ubiquitous in engineering applications, ranging from material processing methods such as friction stir processing/extrusion and in tribological contacts. However, analyzing the microstructural evolution of materials while they are undergoing high speed shear deformation have been a long-standing challenge [1]. This led to predominant reliance on ex situ microscopy before and after shear deformation [1, 2]. But ex situ microscopy lacks the ability to analyze dynamic and transient hierarchical microstructural evolution mechanisms that could occur during shear deformation of materials. Therefore, to better understand the dynamic mechanisms of mass and energy transfer in materials under shear deformation, we developed a first of its kind high-speed rotational diamond anvil cell (HS-RDAC) for synchrotron-based in situ high-energy x-ray diffraction (XRD) (Figure 1 (a, b). We studied the time resolved lattice strain evolution, XRD peak broadening and changes in spatial variation of shear deformation induced alloying in pure metal and metal alloy sheets and powder mixture using the HS-RDAC. These in situ results were combined with detailed ex situ microstructural characterization before and after the shear deformation using transmission electron microscopy and atom probe tomography, which revealed the different stages of evolution of a shear deformation induced hierarchical nanostructure. Multiscale computational simulations including computational fluid dynamics, crystal plasticity, molecular dynamic simulation and density functional theory uncovered the mechanisms behind morphological changes, evolution of defect structures and changes in driving force for shear deformation induced intermixing. This in situ HS-RDAC capability, in combination with ex situ microstructural characterization and computational simulations, can provide new insights into the hierarchical microstructural evolution pathway during shear deformation. Figure 1. (a) The schematic of the high-speed rotational diamond anvil cell (b) the photograph of the HSRDAC installed at the beamline. References: [1] P Bellon, RS Averback, F Ren, N Pant, Y Ashkenazy, JOM, 73, 7 (2021), p 2212-2224. https://doi.org/10.1007/s11837-021-04709-8 [2] B Gwalani, M Olszta, S Varma, L Li, A Soulami, E Kautz, S Pathak, A Rohatgi, P V Sushko, S Mathaudhu, C A Powell, A Devaraj, Communications Materials, 1, 1, 85 (2020). https://doi.org/10.1038/s43246-020-00087-x [3] The authors acknowledge funding from the Laboratory Directed Research and Development (LDRD) funding as a part of the Solid Phase Processing Science Initiative (SPPSi) from the Pacific Northwest National Laboratory. Some of the experiments are conducted using facilities at the Environmental Molecular Sciences Laboratory, a DOE national user facility funded by the Biological and Environmental Research Program and located at Pacific Northwest National Laboratory. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA's Office of Experimental Sciences. The Advanced Photon Source is a U.S. 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.