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Herein, we report transparent LaGdZr 2 O 7 nano-grained ceramics with an average grain size of 10 nm prepared using the high-pressure sintering method at 5.0 GPa/450 °C. These ceramics showed improved plastic deformation as compared to transparent micro-grained LaGdZr 2 O 7 ceramics. Moreover, the fracture toughness of the nano-grained ceramics reached up to 3.4 MPam1/2, which is 79 % higher than that of the micro-grained samples. This improvement in the fracture toughness of the nano-grained ceramics was associated with the presence of a large number of weak grain boundaries in them. [ABSTRACT FROM AUTHOR]

Cubic boron nitride (cBN), a typical superhard material, has garnered significant interest for both fundamental scientific research and technical applications. Here, nanostructured cBN with high-density nanotwins and stacking faults was synthesized by rapid quenching using hexagonal boron nitride (hBN) as the starting material at a moderate temperature (2200 K) and low pressure (13 GPa). This synthetic nanostructured cBN exhibits high Vickers hardness (78 GPa), high fracture toughness (11.8 MPa·m1/2), and extremely high oxidization temperature (1565 K). We propose that the refined grain structure and excellent mechanical properties of the cBN synthesized in this study is attributed mainly to dislocation slips and (111) mechanical nanotwins that dominate this phase transformation. [ABSTRACT FROM AUTHOR]

High-performance polycrystalline cubic boron nitride (PcBN) was sintered without binders at 1500 °C in a pressure range from 11 to 15 GPa using commercial micrometre cubic boron nitride (cBN) with a diameter of approximately 2–4 μm. The results demonstrated that the sample sintered at 12 GPa and 1500 °C had the best mechanical properties and thermal stability. Its average Vickers hardness, fracture toughness, and thermal stability was 63 GPa, 15 MPa m1/2, and 1315 °C, respectively. The considerable improvement in the mechanical properties was mostly attributed to the high compactness, close bonding between grains, and the sample's internal defect structures. The relatively small specific surface area of the micron grains provides an advantage due to its high thermal stability. The amorphous regions observed in the sample's local areas may provide a new strengthening mechanism under high pressure and temperature. [ABSTRACT FROM AUTHOR]

Abstract A series of pure HfB 2 ceramics have been prepared by sintering nano-grained powder using high-energy ball milling at 700–1600 °C and 5.5 GPa. The HfB 2 ceramics are characterized via various techniques for their residual stress, grain size, density, microstructures and defects, hardness, fracture toughness, thermal stability, and oxidation resistance. All properties strongly depend on the treatment temperature, but the exact manner of dependence for each property varies. The results identified that the HfB 2 ceramic sintered at a relatively low temperature of 1000 °C and 5.5 GPa – a bulk pure nano-grained composite for the first time – has the best overall performance. It has a relative density of 99.6%, a Vickers hardness of 26 GPa, a fracture toughness of 5.2 MPa m1/2, and excellent thermal stability and oxidation resistance at high temperatures. Additional strengthening and stabilizing effects are provided by microstructures and defects such as large-angle grain boundaries, stacking faults and twinning. Simultaneous high temperature and high pressure is an effective sintering route for HfB 2 ceramics with grain-size ranging from nanometer to micron. [ABSTRACT FROM AUTHOR]