Experimental study of carbides in the Ti–Cr–C system

The Ti–Cr–C system has been studied by producing samples within the MC–M3C2–M7C3 (M = Ti, Cr) and MC–M3C2–graphite equilibria. The main purpose was to determine the solubility of Cr in MC; however, the solubility of Ti in $$\hbox {M}_3\hbox {C}_2$$ and $$\hbox {M}_7\hbox {C}_3$$ was also of interest, as well as the C content in MC. Heat treatments have been performed at 1673 and 1773 K for 300 h. Thereafter, the phase compositions have been measured with energy-dispersive X-ray spectroscopy (EDS) and wavelength-dispersive X-ray spectroscopy (WDS). X-ray diffraction (XRD), in combination with Rietveld refinement, has been used to determine the lattice parameter for MC. Density functional theory (DFT) calculations were performed to estimate the lattice parameter for MC as a function of composition, and the Rietveld refined lattice parameters for MC have then been recalculated to compositions in order to verify the EDS measurements. The results show that the EDS and XRD measurements give equal results. One conclusion is that, with the current conditions, 300 h is a sufficient heat treatment time in order to reach thermodynamic equilibrium. The other main conclusion is that the solubility of Cr in MC, in general, was overestimated by previous studies due to too short heat treatment times, but also that the solubility is very temperature dependent, especially for the MC–M3C2–graphite equilibrium. This clear temperature dependence was not taken into account in the existing thermodynamic description found in the literature.