Abstract
A number of potentially super-hard materials were examined using ab-initio methods. Low Gibbs free energy polymorphs of diamond-like materials for y = 0 to 7 in the stoichiometric type C8-y By, were identified at absolute zero of temperature. These were proposed as possible super-hard materials with useful applications. The materials with y = 0 to 3, that is, diamond (C), cubic C7B (c-C7B), rhombohedral C3B (r-C3B) and orthorhombic C5B3 (o-C5B3) were found to be dynamically and mechanically stable. A diamond standard was used as a stable comparison. Results of their bulk modulus calculations suggest that these materials were potentially super-hard in character. Systematic trends were established, the hardness was observed to reduce with increasing boron content. The materials under study were all determined as being brittle with diamond being the most brittle, C3B and C5B3 are the least brittle with B/G values of 1.32. Of the materials studied, diamond was determined to have the lowest degree of elastic anisotropy with a Universal Elastic Anisotropy Index of only 0.041 while C5B3 had the highest anisotropy of 1.160, making it the most susceptible to micro-cracks. Our electronic band structure studies of c-C7B, which was predicted to be the hardest in the C8-y By system after diamond, showed that the top of the valence band was about 1.7 eV above the Fermi level with a band gap between the valence and conduction bands, making c-C7B a hole-type conductor having a likely increase in conductivity with increased applied hydrostatic pressure. Key words: Phase stability, elastic anisotropy, ultra-hard material.
Highlights
Super-hard materials have important applications in high speed machining tools for cutting and drilling as well as abrasives and wear-resistant coatings because of their strength
Materials with super-hard characteristics are known to have a value of the bulk modulus that exceeds 250 GPa (Lowther, 2000)
We study the energetic, dynamical, mechanical and anisotropic properties of diamond-like materials for y = 0 to 7 in the stoichiometric type C8-y By
Summary
Super-hard materials have important applications in high speed machining tools for cutting and drilling as well as abrasives and wear-resistant coatings because of their strength. Diamond is extremely hard but at high temperatures and in the presence of oxygen it becomes unstable due to oxidation reactions (John et al, 2002). It is not suitable for machining steel and other alloys of iron because of its redox reactions with iron and some other metallic elements (Nassau and Nassau, 1979) at temperatures exceeding 80 K. Cubic boron nitride (c-BN) is a super abrasive which is more thermally stable than diamond and is better suited for machining steel. Despite the high oxidation resistance temperature and high chemical inertness of c-BN, it is only about half as hard as diamond (Singh, 1986). The possible replacement of both diamond and c-BN by better
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
