Diamond is the hardest naturally occurring material found on earth but single crystal diamond is brittle due to the nature of catastrophic cleavage fracture. Polycrystalline diamond compact (PDC) materials are made by high pressure and high temperature (HPHT) technology. PDC materials have been widely used in several industries. Wear resistance is a key material property that has long been pursued for its valuable industrial applications. However, the inevitable use of catalysts introduced by the conventional manufacturing process significantly reduces their end-use performance and limits many of their potential applications. In this work, an ultra-strong catalyst-free polycrystalline diamond compact material has been successfully synthesized through innovative ultra-high pressure and ultra-high temperature (UHPHT) technology. These results set up new industry records for wear resistance and thermal stability for PDC cutters utilized for drilling in the oil and gas industry. The new material also broke all single-crystal diamond indenters, suggesting that the new material is too hard to be measured by the current standard single-crystal diamond indentation method. This represents a major breakthrough in hard materials that can expand many potential scientific research and industrial applications.

We report experimental results of phase stability and incompressibility of CrN. The obtained bulk moduli for cubic and orthorhombic CrN are 257 and 262 GPa, respectively. These results invalidate the conclusion of phase-transition-induced elastic softening recently reported based on nonmagnetic simulations for cubic CrN [Nature Mater. 8, 947 (2009)]. On the other hand, they provide the only experimental evidence to support the computational models involving the local magnetic moment of Cr atoms [Nature Mater. 9, 283 (2010)], indicating that atomic spin has a profound influence on the material's elastic properties. We also demonstrate that nonstoichiometry in CrN${}_{x}$ has strong effects on its structural stability.

Quantitative measurements of pressure gradients have been made in the pyrophyllite and magnesium oxide (MgO) pressure-transmitting mediums using large-volume cubic apparatus. The relationships of pressure gradients along the axis of symmetry of the pyrophyllite and MgO cubes versus corresponding cell pressures have been established at room temperature. Our experimental results indicated that the pressure gradients increase as the cell pressure increases and that the pressure gradient in the MgO pressure-transmitting medium is about twice as high as that in the pyrophyllite pressure-transmitting medium at the same cell pressure. When the cell pressure reaches 5.5 GPa, the pressure gradient along the axis of symmetry of the pyrophyllite cube is about 50 MPa/mm. When the cell pressure reaches 7.7 GPa, the pressure gradient along the axis of symmetry of the MgO cube is about 140 MPa/mm. The experimental data obtained in the present work not only adapt to the cubic apparatus but also provide reference for the tetrahedral press and the double-stage multi-anvil apparatus (the octahedral compression).