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The stability of nanostructured metal alloys is currently being extensively investigated, and several mathematical models have been developed to describe the thermodynamics of these systems. However, model capability in terms of thermal stability predictions strongly relies on grain boundary-related parameters that are difficult to measure or estimate accurately. To overcome this limitation, a novel theoretical approach is proposed and adopted in this work to identify W-based nanocrystalline alloys which are potentially able to show thermodynamic stability. A comparison between model outcomes and experimental findings is reported for two selected alloys, namely W-Ag and W-Al. Experimental results clearly highlight that W-Ag mixtures retain a segregated structure on relatively coarse length scales even after prolonged mechanical treatments. Moreover, annealing at moderate temperatures readily induces demixing of the constituent elements. In contrast, homogeneous nanostructured W-Al solid solutions are obtained by ball milling of elemental powders. These alloys show enhanced thermal stability with respect to pure W even at high homologous temperatures. Experimental evidences agree with model predictions for both the investigated systems.

Transition metal dichalcogenide (TMD)-based coatings are known for their low friction performance, which is attributed to the formation of a tribolayer consisting almost exclusively of pure well-ordered TMD. However, the formation of such a tribolayer and its wear track coverage is still unknown. In this study, we employed surface mapping and nanotribological techniques to study the properties of the wear tracks of composite W-S-C coatings. Our analysis revealed that the as-deposited coating consisted of two phases, with significantly different nanoscale frictional properties. We attributed the phases to nanocrystalline WS 2 (low friction) and amorphous solution of carbon and WS 2 (high friction). The two phases wear at different rates, especially at lower loads, where we observed faster depletion of nanocrystalline WS 2 . In the wear track, sparse flat WS 2 flakes were identified, suggesting that the recrystallization of the WS 2 phase occurs only at the spots where the contact pressure is the highest.

Achieving the theoretical strength of a metallic alloy material is a demanding task that usually requires utilizing one or more of the well-established routes: (1) Decreasing the grain size to stop or slow down the dislocation mobility, (2) adding external barriers to dislocation pathways, (3) altering the crystal structure, or (4) combining two of the previous discrete strategies, that is, implementing crystal seeds into an amorphous matrix. Each of the outlined methods has clear limitations; hence, further improvements are required. We present a unique approach that envelops all the different strength-building strategies together with a new phenomenon-phase transition. We simulated the plastic deformation of a Zr-Nb nanolayered alloy using molecular dynamics and ab initio methods and observed the transition of Zr from hexagonal close-packed to face-centered cubic and then to body-cenetered cubic during compression. The alloy, which was prepared by magnetron sputtering, exhibited near-theoretical hardness (10.8 GPa) and the predicted transition of the Zr structure was confirmed. Therefore, we have identified a new route for improving the hardness of metallic alloys.

The application of magnetic oxides in spintronics has recently attracted much attention. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors. To combine oxide spintronics and semiconductor technology, we fabricated Fe 3 O 4 films through epitaxial growth on a Si(111) substrate by inserting a γ-Al 2 O 3 buffer layer. Both of γ-Al 2 O 3 and Fe 3 O 4 layer grew epitaxially on Si and the films exhibited the magnetic and electronic properties as same as bulk. Furthermore, we also found the buffer layer dependence of crystal structure of Fe 3 O 4 by X-ray diffraction and high-resolution transmission electron microscope. The Fe 3 O 4 films on an amorphous-Al 2 O 3 buffer layer grown at room temperature grew uniaxially in the (111) orientation and had a textured structure in the plane. When Fe 3 O 4 was deposited on Si(111) directly, the poly-crystal Fe 3 O 4 films were obtained due to SiO x on Si substrate. The epitaxial Fe 3 O 4 layer on Si substrates enable us the integration of highly functional spintoronic devices with Si technology.