Neutron Diffraction Study of Phase Transformations at the Lower Boundary of the Homogeneity Range of Cubic Titanium Carbide TiCx

A neutron diffraction study was made of phase transformations in cubic titanium carbide TiCx at the lower boundary of the homogeneity range TiC0.33–TiC0.47. It was found that the lower boundary of the homogeneity range of the disordered face-centered cubic δ-phase of titanium carbide at 1475 K is at the composition TiC0.33. The high-temperature metastable δ-phase in the composition range TiC0.33–TiC0.47 remains structurally stable at T ≤ 800 K. It was shown that the lower boundary of the homogeneity range of the stable ordered cubic single δ'-phase is at the composition Ti2C0.98. Below this composition, the stable δ'‑phase in the composition range Ti2C0.66–Ti2C0.94 was observed in equilibrium with α-Ti, which suggested that the lower boundary of the homogeneity range of the stable δ'-phase is at the composition Ti2C0.66. In the equilibrium state, the degree of long-range order and the size of antiphase domains in the δ'-phase increase with decreasing carbon content.

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