Electronic mechanism of hardness enhancement in transition metalcarbonitrides

Journal Article · Sat Aug 01 04:00:00 EDT 1998 · Science

OSTI ID:898260

Jhi, Seung-Hoon; Ihm, Jisoon; Louie, Steven G; Cohen, Marvin L

Transition-metal carbides and nitrides are hard materials widely used for cutting tools and wear-resistant coatings. Their hardness is not yet understood at a fundamental level. A clue may lie in the puzzling fact that transition-metal carbonitrides that have the rock-salt structure (such as TiC[x]N[1-x]) have the greatest hardness for a valence-electron concentration of about 8.4 per cell[1-3], which suggests that the hardness may be determined more by the nature of the bonding than by the conventional microstructural features that determine the hardness of structural metals and alloys. To investigate this possibility, we have evaluated the shear modulus of various transition-metal carbides and nitrides using ab initio pseudopotential calculations. Our results show that the behavior of these materials can be understood on a fundamental level in terms of their electronic bandstructure. The unusual hardness originates from a particular band of sigma bonding states between the non-metal porbitals and the metal-porbitals that strongly resists shearing strain or shape change. Filling of these states is completed at a valence-electron concentration of about 8.4, and any additional electrons would go into a higher band which is unstable against shear deformations.

• Research Organization: COLLABORATION - Seoul NationalU./Korea
• Sponsoring Organization: USDOE Director, Office of Energy Research
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 898260
• Report Number(s): LBNL--42223
• Journal Information: Science, Journal Name: Science Journal Issue: 6732 Vol. 399; ISSN 0193-4511; ISSN SCEHDK
• Country of Publication: United States
• Language: english

Related Subjects

36 MATERIALS SCIENCE
CARBONITRIDES
CHEMICAL BONDS
ELECTRONIC STRUCTURE
HARDNESS
MICROSTRUCTURE
SHEAR PROPERTIES
TRANSITION ELEMENT COMPOUNDS