PHASE-EQUILIBRIA IN THE SYSTEMS TI-C-N, ZR-C-N AND HF-C-N

The phase equilibria at 1150 degrees C in the solid regions of the systems Ti-C-N, Zr-C-N and Hf-C-N were investigated by means of are-melted as well as hot-pressed alloys which were analysed for nitrogen and carbon and investigated by X-ray diffraction, metallography and electron probe microanalysis. In the Ti-C-N system the delta-Ti(CxN1-x)(1-y) phase has a broader homogeneity range with respect to the ([C]+[N])/[Ti] ratio than do the f.c.c. boundary phases TiN1-y and TiC1-y. The subnitride phase zeta-Ti4N3-x does not perceptibly dissolve any carbon. In the Zr-C-N system the metal-rich phase boundary of the delta-Zr(CxN1-x)(1-y) phase follows a nearly straight line between ZrC1-x and ZrN1-x. Phase diagrams of the Ti-C-N and Zr-C-N systems are presented. Owing to the low diffusion rates of carbon and nitrogen and the resulting inhomogeneous samples, the Hf-C-N system could be delineated but not clarified with respect to the phase equilibria where the hafnium subnitride phases are involved. Similarly to the delta-Ti(CxN1-x)(1-y) phase, the delta-Hf(CxN1-x)(1-y) phase has a broader homogeneity range than HfC1-y and HfN1-y have.