Carbon – Chromium – Titanium

Abstract

Interest in the C-Cr-Ti system was motivated by the development of new advanced materials. These are nickelor cobalt-bonded TiC alloys (additionally alloyed with chromium carbide), Ti metal-matrix composites (where the matrix is one of the well known beta-alloys, such as Ti-13V-11Cr-3Al (UNS R58010), Ti-3Al-8V-6Cr-4Zr-4Mo (Beta C), Ti-15V-3Al-3Cr-3Sn (Ti-15-3), Ti-5Al-2Sn-2-Zr-4Mo-4Cr (Ti-17) and the strengthening phase is titanium carbide [2001Man, 2003Che]), and Cr-based refractory alloys strengthened by titanium carbide particles [1996Iva2, 2001Iva]. The solid solubility of chromium carbide, Cr3C2, in titanium carbide, TiC, was investigated to some extent by [1936Mol] who found that the solubility limit at 1600°C was less than 70 mass% Cr3C2 and at 1000°C it was less than 40 mass% Cr3C2. [1954Car] reported the results of studies of the solid solubility Cr3C2 in TiC over the temperature range 1250-1900°C. In addition, the rest of the quasibinary system TiC-Cr3C2 has been studied in outline by using metallographic methods. [1960Ere] made a preliminary study of the C-Cr-Ti system. They examined the microstructure of three ternary alloys with compositions located at the intersection points of the Cr-TiC line with the Ti-Cr3C2, Ti-Cr7C3, and Ti-Cr4C (Cr23C6) joins. Based on the metallography and a comparison of the Gibbs energies of formation of titanium and chromium carbides, [1960Ere] concluded that the phase equilibria in this system favor the formation of TiC, and that the Cr-TiC section may be quasibinary. [1962Kur] examined the effect of carbon on the temperature of the beta transformation in titanium-chromium alloys. Thermal analysis of titanium alloys with 2 at.% C and between 0 and 16.6 at.% Cr showed that carbon increases the temperature of the eutectoid transformation in Ti. The carbide phase that separates in these alloys contained only TiC. But the eutectoid temperature reported by [1962Kur] was 728°C rather than 667°C as accepted in the present assessment in accordance with [2000Zhu]. Partial isothermal sections at 1100, 800, and 600°C in the Ti corner of the phase diagram were constructed by [1962Kur]. [1966Ras] studied phase equilibria over the entire composition range and the isothermal section at 1350°C has been presented. [1973Guh] examined alloys of the Cr-TiC section and reported that it is quasibinary of the eutectic type. But the eutectic temperature reported by [1973Guh] (1100°C) was in serious contradiction with the results of [1966Ras] and [1972Fil], who annealed Cr-based alloys at 1350°C but observed no melting. Phase equilibria in the partial Cr-Ti-TiC system were studied by [1982Iva, 1985Iva1, 1985Iva2]. It was shown, that a partially quasibinary section with the eutectic temperature of 1670°C is located on the Cr0.069Ti0.031-TiC0.8 section [1985Iva1, 1985Iva2]. A projection of the solidus surface of the partial Cr-Ti-TiC system as well as isothermal sections of the Cr rich corner at 1527 and 1350°C have been presented by [1985Iva2]. These results were confirmed using thermodynamic modeling by [1984Dan] and experimental studies performed by [1990Ere]. [1990Ere, 1990Sle] constructed the fusion diagram projection, reaction scheme and a number of vertical sections. All of these results were reviewed briefly by [1994McH]. An extensive study of this system was conducted by [1997Boo]. The melting behavior of ternary alloys in the C-Cr-Ti system was investigated using 48 different compositions. DTA studies were carried out on 24 ternary alloys. The ternary alloys fabricated for melting point determination, DTA, and solid state studies were prepared by short duration (2-5 min) hot pressing of blended mixtures of the elemental powders of Ti, Cr, C and/or the carbides TiC and Cr3C2. Temperatures of 1300°C and 1500°C were selected for the solid state investigation of the system. The liquidus surface, as well as isothermal sections at 1300, 1390, 1510, 1650, 1790, 2000, and 2800°C were constructed based on the results of TA, DTA and X-ray diffraction. These results were reviewed by [1999Ban]. On the basis of the results presented by [1997Boo], and using the C-Ti [1998Oka], Cr-Ti [Mas2], and C-Cr [Mas2] binary systems, a reaction scheme and liquidus surface have been drawn by [1999Ban] after corrections in accordance with the accepted binaries.