Transition metal nitrides mechanical properties

These materials are generally black and hard since thin films are easy to lay down [273], some are used as tool coatings [ 274J. These desirable mechanical properties have made transition metal nitrides the subject of several reviews [275. 276. 277J and books [278. 279],... 

Transition element carbides and nitrides are applied as cutting tools because of their extreme hardness and wear resistance. In some cases nitrides and carbides (e.g., of titanium) form solid solutions over the entire compositional range other transition metal nitrides and carbides exhibit fairly different structures and are not completely soluble. Carbon contents within the range of few percentage points usually do not influence the mechanical properties of transition metal nitrides, and vice versa. Hence, completely carbon-free nitrides or nitrogen-free carbides are not required, especially for the titanium compounds. 

A mixture of metallic, covalent and ionic components prevails in the bonding of transition metal carbides, nitrides, and carbonitrides. The metallic character is shown by the high electrical conductivities of these compounds. The bonding mechanism has been described extensively by a variety of approaches for calculating the density of states (DOS) and hence the electron density in f.c.c. transition metal carbides, nitrides, and oxides [11]. In the DOS of these compounds there is a minimum at a valence electron concentration (VEC) of 8, which corresponds to the stoichiometric composition of the group ivb carbides TiC, ZrC, and HfC. Transition metal carbides have a lower DOS at the Fermi level than the corresponding transition metal nitrides, hence the electrical properties such as electrical and thermal conductivity and the superconducting transition temperature, T, are lower than those of the nitrides. 

The summary provided here illustrates the mechanical properties that characterize the transition metal carbides and nitrides. The materials are hard, strong, and somewhat brittle, and resemble ceramic substances. These properties are reviewed by Santhanam (chapter 2), who also describes the commonly used cobalt-binded cermets. 

Carbides and nitrides based on the transition metals of Groups 4 through 6 of the Periodic Table have a number of special physical and mechanical properties that make them attractive for use in engineering applications. This paper discusses these properties and how they are exploited in cemented carbides and carbonitrides used in metalcutting and nonmetalcutting applications. 

This is the first book devoted to the theoretical modelling of refractory carbides and nitrides and alloys based on them. It makes use of computational methods to calculate their spectroscopic, electric, magnetic, superconducting, thermodynamical and mechanical properties. Calculated results on the electronic band structure of ideal binary transition-metal carbides and nitrides are presented, and the influences of crystal lattice defects, vacancies and impurities are studied in detail. Data available on chemical bonding and the properties of multi-component carbide- and nitride-based alloys, as well as their surface electronic structure, are described, and compared with those of bulk crystals. 

The papers presented in the conference span the spectrum of activity in the science of alloys. The theoretical presentations ranged in content from fundamental studies of electronic structure, to first-principles calculations of phase diagrams, to the effects of charge transfer, to the temperature dependence of short-range order parameters. They encompassed the study of mechanical properties, the properties of dislocations, of phase evolution, and computer simulations. Experimental studies were presented based on a variety of state of the art experimental techniques, from TEM to synchrotron diffraction. The phenomena studied varied from the precipitation of nitrides in steel, to the wetting of interfaces between two different crystal structures, to the ordering of vacancies in carbides. And the materials whose properties were measured ranged from Transition metals, to the Lanthanides, to the Actinide series of compounds and alloys. 

Studies in the past few decades have shown that carbides and nitrides of early transition metals, such as V, Ti, Mo, W, Nb, etc., possess useful electrical, magnetic, mechanical, and optical properties (7). Since then, newer applications other than their traditional use in structural materials and cutting tools have been investigated (2). One of these applications has been catalysis where numerous studies have shown activity resembling those exhibited by noble group elements (i). The catalytic activity of these compounds is believed to be due to modification of the crystalline and electronic structure of the parent metal by the presence of the non-metal component (2,4,5). 

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