HIGH-TEMPERATURE PROPERTIES OF TICN-MO2C-CO CERMETS STUDIED BY MECHANICAL SPECTROSCOPY

Low frequency internal friction measurements were performed on TiC0.7N 0.3-Mo2C-Co cermets in an inverted torsion-pendulum working with force d oscillations. A thermally activated high temperature background and three thermally activated peaks were observed in the internal friction spectra. Two peaks, which are stable during thermal treatments, appea r (at 1 Hz) at about 1050 K and 1200 K respectively. The third peak, a ppearing at about 950 K, is only observed during the first heating of the as-received samples. In order to locate the relaxation phenomena, similar measurements were performed on carbide-carbonitride skeletons, in which the metallic binder phase was chemically removed. Complement ary microstructural characterizations, performed by conventional TEM, allow one to identify the physical mechanisms responsible for the IF p eaks and background.