Tantalum nitride (TaN) compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and hightemperature (HPHT) method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressurevolume (P-V ) sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B 0 = 369(2) GPa with pressure derivatives of B 0 = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result (B 0 = 351 GPa), which is close to the recent theoretical calculation result (B 0 = 378 GPa). An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.

Nano-sized MgAl2O4 powders were treated at 500~1000 oC in a vacuum of 10-3Pa for 2 h, and then sintered at 500~900 oC under 1~6 GPa. The powders with and without vacuum-heat-treatment were investigated by means of Transmission Electron Microscope (TEM) and Sedimentation Test. It was found that the vacuum-heat-treatment of nano powder could effectively get rid of the absorbed gas on the surface of nano-particles. Bulk nanostructured transparent ceramics without cracks were sintered easily with the treated nano-sized powder. The success rate of nano-sinterning of bulk transparent ceramics was greatly increased when a suitable vacuum-heat-treatment process was used for the starting nano-sized powder.

Cubic boron nitride (cBN) is a excellent super hard materials with superior mechanical properties that has been widely used in different industrial applications. Conventional cBN was sintered with binder in the cBN powder, and the binder affect the mechanical properties of cBN. Here we report that we sinter the polycrystalline cBN on WC-16wt%Co substrates without any sintering agent at the pressure 5.5 GPa and temperatures of 1300-1600°C for 10 min. In the sintering, we used 1-2μm fine grained cBN powder as the starting materials, also, liquid substance infiltrated from the substrates and occurred chemical reactions with cBN powder. Reaction contents were investigated at different temperatures according to X-ray diffraction (XRD). Plenty of direct BN-BN bonding was formed in the scanning electron microscopy ( SEM) observation.The hardness of best samples reach 38.5 GPa under the loading force of 5 kg, which have high hardness for the formation of direct BN-BN fine grains in the sample. .

This paper aims to study the sintering process and mechanical properties of submicron polycrystalline diamond (SMPD) without any secondary phases and binder materials under pressure of 7-8 GPa and 1400 °C-1800 °C, using the bi-layer assembly and the conventional assembly methods. The as prepared samples were characterized by X-ray diffraction, scanning electron microscope, and Vickers indenter hardness tests. Well sintered specimen was obtained under the condition of 8 GPa and 1600 °C using the bi-layer assembly method, and an indentation test demonstrated a Vickers hardness of 52 GPa. The graphitization of diamond was found to be an important factor determining the hardness of samples sintered using the bi-layer assembly.