Phase transformations in the W–Cr system at the nanoscale

An Overview of Nano Multilayers as Model Systems for Developing Nanoscale Microstructures

“…Hf-Ti, Mo-Au, Ta-Hf and W-Cr NMMs (2 µm total thickness), comprising alternating mixed and pure solute layers, were deposited on Si (100) substrates via DC magnetron sputtering following procedures described in previous manuscripts [ 17 , 18 , 19 , 20 ]. In these manuscripts, more detailed discussions of both the experimental approach and findings can be found.…”

“…For these scans, the enthalpy of the endothermic and exothermic transformations was measured over a baseline that was extracted using Origin Lab. In order to experimentally observe the microstructural changes correlating to these transformations, each multilayer system was annealed for 96 h at various temperatures up to 1000 °C inside a GSL1100X vertical tube furnace (MTI Corporation, Richmond, CA) under vacuum (5 × 10 −4 Pa) [ 17 , 18 , 19 , 20 ]. At the end of the heat-treatment, the samples were rapidly quenched in a low vapor pressure oil.…”

“…At the end of the heat-treatment, the samples were rapidly quenched in a low vapor pressure oil. The initial as-sputtered and final tailored microstructures (1000 °C) are the focus of this article in order to capture a more general understanding of the concluding microstructural transformations where details on intermediate microstructures can be found elsewhere [ 17 , 18 , 19 , 20 ]. Transmission electron microscopy (TEM) lamellas exposing the cross-section of the films were prepared via focus ion beam (FIB) lift-out techniques within a JEOL FIB-4500 microscope (JEOL, Tokyo, Japan), where the surface was protected from beam damage with a thin layer of C. The microstructure and local compositions of the films were studied via TEM imaging of the lamellas in a JEOL JEM-2100F TEM (JEOL, Tokyo, Japan) equipped with an Oxford X-MaxN 100 EDS detector.…”

“…Therefore, NMMs can leverage the favorable characteristics of nanostructured materials that can be credited to the high density of grain boundaries (GBs) and interfaces while expanding possible microstructural arrangements. As a result of these valuable attributes, NMMs have demonstrated capability as model systems for developing new equiaxed nanostructured materials [ 16 , 17 , 18 , 19 , 20 , 21 ]. Individual studies on different resulting microstructures are highly encouraging [ 22 , 23 , 24 ], but what remains in question is an overarching view of the mechanistic relationships between different initial multilayer structures and the final nanostructure achieved after thermally-driven microstructural transformations [ 25 ].…”

“…The contributions of both interface properties and composition are generalized to identify global relationships between predictions of nanoscale microstructures and the final observed nanostructured microstructures. In this article, we present the microstructural synergies and differences within four distinct model systems (Hf-Ti [ 18 ], Ta-Hf [ 19 ], W-Cr [ 20 ], Mo-Au [ 17 ]) in their as-sputtered condition and after annealing at 1000 °C for 96 h. These model binary material systems were chosen because they are all predicted to exhibit nanocrystalline stability at high temperatures [ 30 , 31 ]. Furthermore, these systems are non-equiatomic to promote enhanced diffusion on the path toward multi-layered-to-equiaxed microstructural transformations.…”