Experimental Determination of the Solubility of Co in the Cr-Based Carbides Cr23C6, Cr7C3, and Cr3C2

Thermodynamic calculations based on the CALPHAD method are nowadays often applied in the design of new materials due to increasing demands on shorter lead times for development. However, such calculations rely heavily on the assessed thermodynamic descriptions, which in turn rely on the amount and quality of available experimental data, especially for binary and ternary sub-systems. The ternary Co-Cr-C system is an extremely important subsystem to, e.g., multi-component cemented carbide grades, such as W-Co-Cr-M-C (M = Ti,Ta,Nb,V,Zr,Hf), as well as Cr-containing Co-base alloys. In the case of the Co-Cr-C system, there is a lack of reliable data on the solubility of Co in Cr-carbides. Therefore, the present work concerns an experimental study of the solubility of Co in all three of the Cr-based carbides, i.e., Cr23C6, Cr7C3, and Cr3C2. This was done by synthesizing appropriate samples in the M7C3+M23C6+liquid and M7C3+M3C2+graphite three-phase fields. The results show that a recent thermodynamic description of the Co-Cr-C system is unable to reproduce the experimentally determined solubilities. Therefore, the present study provides important input for future alloy development and improvement of the thermodynamic description of the Co-Cr-C system.