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Diamond-like carbon (DLC) coatings enhance tool wear resistance across various temperatures. The sp3/sp2 bond ratio within DLC significantly impacts its properties and thermal stability. Elevated temperatures can alter DLC's structure, while metallic elements and interlayers like chromium can modify its microstructure and performance. To evaluate the potential of W-DLC coatings with a chromium interlayer on 40CrMoV5-1 hot work tool steel under elevated temperatures, mechanical and tribological properties were assessed at room temperature and at temperatures of 100, 200, 300, 400, and 500 °C. Nanoindentation revealed a maximum hardness of 14.1 ± 1.3 GPa for the coating deposited at room temperature, attributed to a high sp3 content confirmed by Raman spectroscopy. Hardness decreased to 9.3 ± 1.0 GPa at 400 °C due to graphitization. The elastic modulus remained relatively constant across all temperatures. Tribological tests indicated a low coefficient of friction (CoF) of 0.15 at room temperature, increasing to 0.35 at 100 °C. The CoF further rose to 0.5 at 200 °C, coinciding with increased graphitization. However, the CoF reduced to 0.45 and 0.35 at 400 °C and 500 °C, respectively, likely due to the formation of a WO3 tribo-film and the protective effect of the chromium interlayer. [ABSTRACT FROM AUTHOR]

In the realm of advanced anode materials for lithium-ion batteries, this study explores the electrochemical performance of a high-entropy oxide (HEO) with a unique spinel structure. The equiatomic composition of CrMnFeCoCu was synthesized and subjected to a comprehensive materials characterization process, including X-ray diffraction and microscopy techniques. The multicomponent alloy exhibited a multiphase structure, comprising two face-centered cubic (FCC) phases and an oxide phase. Upon oxidation, the material transformed into a spinel oxide with a minor presence of CuO. The resulting high-entropy oxide demonstrated excellent electrochemical behavior when utilized as an anode material. Cyclic voltammetry revealed distinctive reduction peaks attributed to cation reduction and solid electrolyte interphase (SEI) layer formation, while subsequent cycles showcased high reversibility. Electrochemical impedance spectroscopy indicated a decrease in charge transfer resistance during cycling, emphasizing the remarkable electrochemical performance. Galvanostatic charge/discharge tests displayed characteristic voltage profiles, with an initial irreversible capacity attributed to SEI layer formation. The HEO exhibited promising rate capability, surpassing commercial graphite at higher current densities. The battery achieved 80% (275 mAh g−1) of its initial stable capacity at a current density of 500 mA g−1 by the 312th cycle. Post-mortem analysis revealed structural amorphization during cycling, contributing to the observed electrochemical behavior. This research highlights the potential of HEOs as advanced anode materials for lithium-ion batteries, combining unique structural features with favorable electrochemical properties. [ABSTRACT FROM AUTHOR]

In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g−1. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g−1, an incredible discharge capacity of 543 mAh g−1 was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

This study shows that in an atmosphere containing water vapor, the oxide layer on the surface of the 9CrNB steel MarBN (Martensitic 9Cr steel strengthened by Boron and MX Nitrides) was formed by an outer layer of hematite Fe2O3 and Cr2O3 and an inner two-phase layer of Fe3O4 and Fe3O4 + (Fe, Cr)2O4, which was confirmed by XRD analysis. Part of the layer consisted of nodules and pores that were formed during the increase in oxides when the present H2O(g) acted on the steel surface. The diffusion mechanism at temperatures of 600 and 650 °C and at longer oxidation times supported the "healing process" with a growing layer of Fe oxides and the presence of Cr and minor alloying elements. The effects of alloying elements were quantified using a concentration profile of the oxide layer based on quantitative SEM analysis, as well as an explanation of the mechanism influencing the structure and chemical composition of the oxide layer and the steel-matrix–oxide interface. In addition to Cr, for which the content reached the requirement of exceeding 7.0 wt. % in the inner oxide layer, W, Co, Mn, and Si were also found in increased concentrations, whether in the form of the present Fe-Cr spinel oxide or as part of a continuously distributed layer of Mn2O3 and SiO2 oxides at the steel-matrix–oxide interface. After long-term high-temperature oxidation, coarser carbides of the M23C6 type (M = Fe,W) significantly depleted in Cr were formed at the oxide-layer/matrix interface. In the zone under the oxide layer, very fine particles of MC (M = V, Nb, and to a lesser extent also Cr in the particle lattice of the given phase) were observed, with a higher number of particles per unit area compared to the state before oxidation. This fact was a consequence of Cr diffusion to the steel surface through the subsurface zone. [ABSTRACT FROM AUTHOR]