Hardness of materials at high temperature and high pressure

• Published in: Philosophical magazine (Abingdon, England) England), 2009-09, Vol.89 (25), p.2117-2127
• Main Authors: Mukhanov, V.A., Kurakevych, O.O., Solozhenko, V.L.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; hardness theory; high pressure; high temperature; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; Specific materials; superhard materials; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; Tribology and hardness
• ISSN: 1478-6435; 1478-6443; 1478-6433
• DOI: 10.1080/14786430903032563

The intrinsic character of the correlation between hardness and thermodynamic properties of solids has been established. The proposed thermodynamic model of hardness allows one to easily estimate hardness and bulk moduli of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements or on the enthalpy at the melting point. The correctness of this approach is illustrated by an example of the recently synthesized superhard diamond-like BC 5 and orthorhombic modification of boron, γ-B 28 . The pressure and/or temperature dependences of hardness were calculated for a number of hard and superhard phases, i.e. diamond, cBN, B 6 O, B 4 C, SiC, Al 2 O 3 , β-B 2 O 3 and β-rh boron. Excellent agreement between experimental and calculated values is observed for temperature dependences of Vickers and Knoop hardness. In addition, the model predicts that some materials can become harder than diamond at pressures in the megabar range.