Densieication of nonstoichiometric titanium carbide during sintering

Densieication of - DENSIFICATION OF NONSTOICHIOMETRIC TITANIUM CARBIDE DURING SINTERING S S Ordan'yan G S Tabatadze and L V Kozlovskii UDC 621.762

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DENSIFICATION OF NONSTOICHIOMETRIC TITANIUM CARBIDE DURING SINTERING S. S. Ordan'yan, G. S. Tabatadze, and L. V. Kozlovskii UDC 621.762 The sintering densification behavior of nonstoichiometric carbides has already been the subject of a number of investigations [1-5], in which it has been established that deviation from stoichiometry substantially accelerates the shrinkage (densification) of these materials. The work described below was undertaken with the aim of studying the effect of deviation from stoichiometry and degree of dispersion of powders of TiC x phases on their densification during sintering. It differed from other, similar investigations in that the starting ma- terials were TiC x phases produced by the method of self-propagating high-temperature synthesis (SHS).* Materials prepared by this method, which involves the utilization of heat liberated in the "combustion" zone, possess a number of specific characteristics: They have a non- equilibrium structure and their structural elements are in a stressed state. Thus, SHS in- troduces additional defects into nonstoichiometric MeC x phases. Some properties of the sub- stances investigated are given in Table i. Powders of the TiC x phases were subjected to vibratory milling under ethyl alcohol for periods ranging from 5 to 60 h. Specific surface determinations upon the milled powders, made by the method described in [6], revealed that the rate of comminution of the phases depended on their stoichiometry only in the initial, 20-h stage of milling. After 60-h comminution the specific surface of all the alloy powders was 5 m2/g. It is interesting to note that the comminution kinetics revealed in our work differed markedly from the comminution kinetics of equilibrium TiC x phases reported in [7]. Specimens were pressed, using a 5% solution of rubber in benzine as lubricant, under a pressure of 1 ton/cm 2. The compacts were dried in a vacuum and then sintered in an SShVL-125/ 25 vacuum furnace at a residual pressure of the order of i0 -~ mm Hg, the holding time at each temperature being 1 h. The sintering was followed by determinations of shrinkage, porosity, volume and relative densities; the relative densities were compared with densities deter- mined by x-ray diffraction. The results obtained revealed that, at any given degree of dis- persion of starting powders (Ssp ~ 4 mS/g), the relative densities of the TiC x phase alloys appreciably grew with increasing deviation from stoichiometry (Figs. 1 and 2). At a constant degree of dispersion the effect of phenomena linked with capillary forces on densification may be assumed to a first approximation to have been the same for all the materials; the different degrees of densification attained must have been due to different contributions from mechanisms controlled by the level of diffusional mobility in the lattices of the TiC x phases. Effective coefficients of self-diffusion in the TiC x phases at various temperatures were calculated with equations proposed in [8, 9].
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This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.

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Densieication of - DENSIFICATION OF NONSTOICHIOMETRIC TITANIUM CARBIDE DURING SINTERING S S Ordan'yan G S Tabatadze and L V Kozlovskii UDC 621.762

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