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Hardness is an important indicator of the wear resistance of tool materials. The study of the effect of hardness on the wear resistance of tool materials has significant practical applications. In this experimental work, a series of polycrystalline cubic boron nitride (PcBN) and diamond (PCD) compacts with different hardness are sintered under high temperature and pressure, and these samples were fashioned into turning tools, used for edge wear testing in the granite turning process. Based on the measurements above, the relationship between hardness and wear resistance in two materials with identical grain sizes (1–2 µm) was examined, and the results reveal a significant positive correlation between the hardness and wear resistance of the two materials. Remarkably, the relationship between hardness and wear resistance in two materials complies with the same type of fitting function. But incredibly, the wear resistance of the two materials exhibits inconsistency as the hardness increases. Specifically, below 40 GPa Vickers hardness, both materials exhibit comparable wear resistance. However, above 40 GPa, the difference in wear resistance between the two materials becomes more pronounced with increasing hardness. At the Vickers hardness of 70 GPa, the abrasion ratio of the PCD is approximately 3.5 times that of the PcBN, and it is anticipated that the disparity between them will continue to expand within the broader range of hardness. Further analysis reveals that the intrinsic hardness of the crystal grains significantly impacts the wear resistance of polycrystalline materials. [ABSTRACT FROM AUTHOR]

A transparent alumina ceramic with a transmittance of 71.7% at 640 nm is fabricated by sintering mixed metastable Al2O3 powder at 5.0 GPa/600 °C. The spherical starting particles are deformed and highly densified during compression, and transformed into α‐Al2O3 at 5.0 GPa/500 °C. High pressure suppresses the growth of transformed grains to produce alumina bulks with an average grain size of approximately 52 nm at 600 °C. In addition, the Hall–Petch effects combined with the pressure‐induced curvilinear grain boundary and Moiré fringe‐like defects enhance the transparent alumina sample to yield a Vickers hardness of 26.4 GPa (0.5 kgf). However, these microstructures do not enhance the fracture toughness of the transparent alumina ceramics. [ABSTRACT FROM AUTHOR]

Carbon has been proposed to be a potential light element in the Earth's solid inner core. However, its presence and concentration in the core remain limited constrained. In this study, we measured the equation of state of an iron‐carbon alloy with ∼1.5 wt.% (∼6.64 at.%) carbon up to ∼185 GPa and ∼3,750 K via shock compression. The Hugoniot equation of state of the Fe‐1.5wt.%C alloy was determined to be Us (km/s) = 3.94 (0.15) + 1.62 (0.08) Up with an initial density of 7.77 (0.03) g/cm3, where Us and Up are the shock wave velocity and particle velocity, respectively. Hugoniot data combined with the Mie‐Grüneisen equation of state allow us to build the thermal equations of state of the Fe‐C alloy at high pressure‐temperature (P‐T) conditions. Investigations on the pressure‐density relation of Fe‐C alloys by the shock experiments and synchrotron X‐ray diffraction measurements by Pamato et al. (2020), https://doi.org/10.1029/2020jb020159 have indicated that carbon should occupy interstitial sites of iron lattice at high P‐T conditions. The thermal equation of state of the Fe‐1.5wt.%C alloy provided here shows that Fe‐1.5wt.%C is ∼1.65% denser than the inner core under conditions relevant to the inner‐core boundary. This study indicates that iron alloyed with an upper bound of ∼2.2 (0.3) wt.% (∼10.7 [1.6] at.%) carbon may match with the Preliminary Reference Earth Model (PREM) in the Earth's inner core. Thus, interstitial carbon in iron helps to explain the observed density deficit of the inner core, although other light elements are also expected. Plain Language Summary: Carbon (C), as an essential life element, is likely to be present in the Earth's core. Previous investigations revealed that carbon would be alloyed interstitially in the hexagonal close‐packed (hcp) iron lattice at high pressures which occurs in the Earth's core and thus affect the thermodynamic and seismic velocities of the core in a different way. In this study, we determined the density of Fe‐1.5wt.%C alloy up to ∼185 GPa and ∼3,750 K via hypervelocity impact experiments. Experimental results were used to develop reliable thermal equations of state for Fe‐1.5wt.%C alloy under the Earth's inner‐core conditions. Our results support that a small amount of carbon may occupy the interstitial sites of hcp‐iron at extreme pressure and temperature, and the proposed model suggests an upper bound of ∼2.2 wt.% carbon in the Earth's inner core assuming it as the major light element. Key Points: Hugoniot equation of state of Fe‐1.5wt.%C alloy has been investigated to ∼185 GPa and ∼3,750 K via shock compressionA certain amount of carbon (e.g., 1.5 wt.%) in solid iron takes the interstitial sites under conditions relevant to the Earth's inner coreAn upper bound of ∼2.2 wt.% carbon is suggested in the Earth's inner core based on the density deficit of the Earth's core [ABSTRACT FROM AUTHOR]

High‐pressure structural evolution of CeOCl, a lanthanide oxychloride, was investigated by in situ high‐pressure Raman scattering and first‐principles calculations. We report the novel observation of discontinuities in Raman wavenumber at the pressure of approximately 7 GPa, which are related to an isostructural phase transformation caused by an increase of Bader charge transfer from Ce to Cl and O. In addition, the mode‐Grüneisen parameters (of CeOCl) were given and discussed. This is helpful for us to better understand applications of the Ce‐based compounds. [ABSTRACT FROM AUTHOR]

Abstract: Ferroelectrics with perovskite‐like layered (PL) structure are well‐known for their high Tc and the application prospect of high‐temperature‐piezoelectric sensing. In this study, the PL‐structure Eu2Ti2O7 was prepared by 1‐step high‐pressure sintering, which show the pyrochlore structure of Eu2Ti2O7 would change into PL structure at 11 GPa, 1300°C. The PL‐structure Eu2Ti2O7 is metastable, which will change back to pyrochlore structure at about 900°C in the air. The PL‐structure Eu2Ti2O7 was confirmed as a high‐temperature ferroelectric material for the first time. The ferroelectric domain switching was directly observed using piezoelectric force microscope. The piezoelectric constant of the PL Eu2Ti2O7 ceramic was measured as 0.7‐0.9 pC/N and its thermal depoling temperature (Td) was determined as 800°C, which is associated with the PL‐pyrochlore transition. [ABSTRACT FROM AUTHOR]

Chromium mononitride (CrN) exhibits interesting magnetic, structural, and electronic properties for technological applications. Experimental reports on these properties are often inconsistent owing to differences in the degree of nonstoichiometry in CrN x. To date, the preparation of bulk and stoichiometric CrN has been challenging; most products are in the form of a thin film produced by non-equilibrium processes, and are often nonstoichiometric and poorly crystallized. In this work, we formulated a solid-state ion-exchange route for the synthesis of CrN under high pressure. The final CrN product is phase-pure, stoichiometric, and well-crystallized in the bulk form. Near-stoichiometric and well-crystallized CrN can be synthesized using the same route at atmospheric pressure, making massive and industrial-scale production technologically feasible. The successful synthesis of stoichiometric and bulk CrN is expected to open new opportunities in diverse areas of fundamental research. [ABSTRACT FROM AUTHOR]

Phase transitions of the title compound are investigated by high pressure in situ DTA up to 5 GPa. [ABSTRACT FROM AUTHOR]