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Hexagonal boron nitride (hBN) was used as the additive in improving the hardness and thermal stability of polycrystalline diamond compact under high temperature and high pressure. Indentation testing on diamond/cubic boron nitride (cBN) composites indicated a Vickers hardness of 96 ± 7 GPa, rivaling the hardness of monocrystal diamond. Thermal gravimetric analysis (TGA) suggested that the composites of diamond/cBN are thermally stable in air up to ∼910 °C which is higher than that of pure polycrystalline diamond compact (∼750 °C). Raman, TGA, x-ray photoelectron spectroscopic and microstructure analyses all revealed the features of diamond/cBN composition beyond both diamond and cBN. [ABSTRACT FROM AUTHOR]

Alumina nano-powder was used as the cement in bonding coarse spherical particles to fabricate transparent alumina ceramics under high pressure and modest temperature. Observations on the microstructure, density and microhardness of Al 2 O 3 specimens prepared at 500–1200 °C under 5.0 GPa provided significant effects of additive nano-particles on the sintering of samples. The high pressure initiated plastic deformation of spherical particles, rearranged nano-particles filling the clearance among spherical particles and bonding each other to densify the products. The additive particles also contribute to grain boundary strengthening to obtain samples with enhanced transparency and microhardness. [ABSTRACT FROM AUTHOR]

Single-phase BC4N can be formed at high pressure and temperature, starting with either a mixture of diamond and cubic boron nitride or graphite and hexagonal boron nitride. The samples exhibit extreme Vickers hardness (85±4GPa), reaching the hardness of single crystal diamond. Within a random solid solution model, the X-ray diffraction patterns of cubic BC x N solid solutions were calculated. The results indicate that the prepared B–C–N materials are continuous solid solutions with a zinc-blende structure. [Copyright &y& Elsevier]

We propose a sintering mechanism of transparent Y3Al5O12 nanoceramics under high pressure. Through analysis of the porosity, grain size and residual stress for the nanostructured YAG compacts prepared at high pressure and modest temperature (HPMT, 2.0–5.0GPa and 300–500°C), the nanosintering behavior was systematically investigated. High pressure can initiate the plastic deformation of nanograins to eliminate pores and enhance the local atomic diffusion among grain boundaries, thus producing fine nanostructured and near fully dense transparent YAG bulks. [Copyright &y& Elsevier]

Pressure is an important thermodynamic parameter in addition to temperature and chemical composition during material sintering process. However, few experimental images intuitively describing the densification process of grains during compression, especially for the high melting point ceramics. Here we observed deformation evolution and mechanical response of spherical alumina particles after high pressure treatment. By analyzing the plastic deformation and grain boundary characters of spherical alumina particles, and the boundary stress and yield stress variation of grains under various pressures and temperatures, a clear picture of the high-pressure powder densification and sintering process is depicted. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report a method combining the top-down and bottom-up approaches for the fabrication of nanocrystalline ceramic, which can break down the Y 2 O 3 nanorods and consolidate the broken nanoparticles to 99.1% relative density. The lab-mad nanorods with a length of about 500 nm and a diameter of about 20 nm, exhibit better compressibility and sinterability than the spherical nanopowders when the compaction pressure exceeds 0.4 GPa and the sintering condition is 5 GPa/500 °C, respectively. The obtained nanocrystalline ceramic shows a maximum transmittance of 81.3% in the infrared region, hardness as high as 10.5 GPa and fracture toughness of 2.21 MPa m1/2. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High-purity (Ta 0.2 Nb 0.2 Hf 0.2 Zr 0.2 Ti 0.2)C high-entropy ceramics are successfully synthesized using high-pressure solid-phase reactions. The high-entropy phase formation route and the effect of pressure tuning on the structural and mechanical properties of the ceramics are systematically investigated. An interesting process is observed whereby a double phase high-entropy carbide is formed, followed by the defusing of one phase into another, and the eventual formation of a high-entropy phase. Moreover, an abnormal, pressure-induced enhancement of the bulk modulus and strength is observed, resulting from the crystal plane distortion in high-entropy carbides. These results reflect the unusual lattice distortion effects of continuous, pressure-induced tuning on the structure and properties of high-entropy carbides. [Display omitted] [ABSTRACT FROM AUTHOR]

Boron suboxide (B 6 O) with superhardness holds great promise for a wide range of practical applications, but suffers from a low fracture toughness due to the formation of unusual nanoscale amorphous bands. Understanding of the underlying deformation mechanisms in this material, however, has been hindered limited experimental evidences. Here we report the discovery of new mechanisms for the formation of amorphous bands in B 6 O under nonhydrostatic pressure, based on in-situ high-pressure optical absorption measurements and analysis of postmortem samples. We find that the bandgap of B 6 O is sensitive to plastic deformation, offering an effective approach for exploring deformation behaviors of this material. Two new amorphous bands are identified along two distinct crystallographic planes of (1 1 ¯ 0 4 ¯) and (4 3 ¯ 1 ¯ 8 ¯) associated with unbonded O-O pairs. Our findings establish a methodology for in-situ probe of plastic deformation in brittle materials, and demonstrate how their properties can be altered by plastic deformations under nonhydrostatic pressures. [Display omitted] [ABSTRACT FROM AUTHOR]

The Vickers hardness of polycrystalline γ-boron (γ-B) was measured using a diamond indentation method. The elastic properties of polycrystalline γ-B were determined using an ultrasonic measurement method. Under a loading force of up to 20N our test gave an average Vickers hardness in the asymptotic hardness region around 30.3GPa. We also measured the hardness and elastic properties of polycrystalline β-B and cubic boron nitride–Ti3SiC2 (PcBN) for comparison. The hardness and elastic properties of polycrystalline γ-B were found to be very close to those of PcBN. [Copyright &y& Elsevier]

A novel method for preparing highly transparent hydroxyapatite bioceramics at relatively low temperatures (325–450°C), i.e. about 60% lower compared with other commonly used preparation methods, has been developed under ultrahigh pressure (UHP; 2.0–5.0GPa). UHP can remarkably restrain grain growth, enhance density and microhardness and we have characterized the morphology, density and mechanical properties of the prepared ceramics. We reason that these bioceramics are highly transparent due to the negligible light scattering from the nanosized grains and pores in the samples. [Copyright &y& Elsevier]