Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials.

Carbon, the fourth most abundant element in the Universe, possesses numerous allotropes with diverse bonding character (sp¹-, sp²- and sp³-hybridized bonds) and structural motif of the constituting atoms. In particular, the carbon materials with a fully or nearly 100% sp³-hybridized strong C-C bonds often lead to excellent mechanical properties, chemical stability, thermal and optical properties, such as crystalline diamond and diamond-like amorphous carbon (DLC). In this review, we systematically summarize the synthesis, microstructure, mechanical properties, thermal and optical properties of ultrahard carbon materials with current experimental results on nano-polycrystalline diamond (NPD), nanotwinned diamond (NTD), micro-grained polycrystalline diamond (MPD), and amorphous diamond/carbon. In addition, we discuss the difference of spectra of XRD, Raman and EELS between various nanocrystalline diamond powder and ultrahard carbon materials. Finally, we provide our insights into the future development and applications in the research of ultrahard carbon bulk materials by high-pressure and high-temperature techniques according to the current advantages, limitations and challenges in the experiment.

We analyse the loading force transmissions for two kinds of loading structures directed at multistage octahedral cell of high pressure device, and build a mechanical relationship for high pressure producing efficiency. The relationship between cell pressure and hydraulic load is calibrated at room temperature for 14/8, 12/6 and 10/4 cell assemblies using the phase transitions of Bi, ZnTe, ZnS and GaAs under high pressure. Also we discuss qualitatively the influences of both mechanical configuration and hardness of last stage anvil on high pressure producing efficiency of octahedral cell. The experimental results show that both mechanical configuration and hardness of last stage anvil are key factors for affecting high pressure producing efficiency, what is more, the mechanical configuration is more important. The larger the geometry configuration of octahedral cell, the higher the high pressure producing efficiency is; high pressure producing efficiency of 6-8 type loading configuration is higher than that of 2-6-8 type loading configuration; when the pressure of octahedral cell approaches to Vickers hardness of last stage anvil, the harder the last stage anvil, the higher the high pressure producing efficiency and the higher cell pressure is.