Amorphous carbonas one of disordered carbon materials usually exhibits different mechanical, electrical, optical and thermal properties from crystalline carbon materials. Exploring high-performance amorphous carbon materials is always a research hotspot. In this paper, a high-strength amorphous carbon composed of onion-like structural elements was reported. This kind of amorphous carbon was obtained via treating carbon black at high temperature and high pressure (i.e., 1700–2000 ℃ and 6 GPa), which shows excellent mechanical properties. The nano indentation hardness, indentation elastic recovery, uniaxial compressive and flexural strength of the sample with best performance are 5.1 GPa, 80.1%, 956.4 MPa and 216.0 MPa, respectively. The compressive and flexural strengths of the amorphous carbon are 5.6 times and 2.8 times greater than those of Toyo Tanso ISO-68 graphite, respectively. This kind of amorphous carbon also has a good conductivity, and its room-temperature resistivity can be as low as 75.7μΩ·m. This high-strength conductive amorphous carbon can be widely used as electrode and mold materials.

As one of the important materials, nanocrystalline Au (n-Au) has gained numerous interests in recent decades owing to its unique properties and promising applications. However, most of the current n-Au thin films are supported on substrates, limiting the study on their mechanical properties and applications. Therefore, it is urgently desired to develop a new strategy to prepare n-Au materials with superior mechanical strength and hardness. Here, a hard n-Au material with an average grain size of ~ 40 nm is prepared by cold-forging of the unique Au nanoribbons (NRBs) with unconventional 4H phase under high pressure. Systematic characterizations reveal the phase transformation from 4H to face-centered cubic (fcc) phase during the cold compression. Impressively, the compressive yield strength and Vickers hardness (H_V) of the prepared n-Au material reach ~ 140.2 MPa and ~ 1.0 GPa, which are 4.2 and 2.2 times of the microcrystalline Au foil, respectively. This work demonstrates that the combination of high-pressure cold-forging and the in-situ 4H-to-fcc phase transformation can effectively inhibit the grain growth in the obtained n-Au materials, leading to the formation of novel hard n-Au materials. Our strategy opens up a new avenue for the preparation of nanocrystalline metals with superior mechanical property.

Glassy carbon (GC) is a type of non-graphitizing disordered carbon material at ambient pressure and high temperatures, which has been widely used due to its excellent mechanical properties. Here we report the changes in the microstructure and mechanical properties of GC treated at high pressures (up to 5 GPa) and high temperatures. The formation of intermediate sp²–sp³ phases is identified at moderate treatment temperatures before the complete graphitization of GC, by analyzing synchrotron X-ray diffraction, Raman spectra, and transmission electron microscopy images. The intermediate metastable carbon materials exhibit superior mechanical properties with hardness reaching up to 10 GPa and compressive strength reaching as high as 2.5 GPa, nearly doubling those of raw GC, and improving elasticity and thermal stability. The synthesis pressure used in this study can be achieved in the industry on a commercial scale, enabling the scalable synthesis of this type of strong, hard, and elastic carbon materials.