HIGH TEMPERATURE MECHANICAL-PROPERTIES OF TI(C,N)-MO2C-NI CERMETS STUDIED BY INTERNAL-FRICTION MEASUREMENTS

Internal friction measurements were performed on TiC0.7No0.3-Mo2C-Ni m etal-bonded refractory materials, in order to study how the compositio n and the microstructure of cermets control the mechanical properties of these materials. A free inverted torsion-pendulum was used, oscilla ting in the 0.2-2 Hz frequency range, up to 1273 K. Isothermal I.F. sp ectra were measured in a forced torsion-pendulum in the 10-10(-4) Hz r ange, and up to 1400 K. One thermally activated I.F. peak at 1100 K (a t 0.5 Hz), is superimposed with a high temperature I.F. background. Th e amplitude of the background and the activation energy of the peak ar e strongly dependent on the Mo and C content in the material. Transmis sion electronic microscope observations give complementary results to identify the relaxation mechanisms. In the physical model proposed to describe the anelastic behaviour of these materials, the 1100 K peak i s attributed to the dragging of Mo atoms by dislocations in Ni-Mo-Ti a lloy, while the high temperature background is associated with long di stance displacements of dislocations in this binder phase. The refract ory skeleton gives a contribution to the high temperature background, and to another peak at 900 K. A comparison is made with I.F. measureme nts in WC-Co, that confirms the specific role of the metallic phase fo r each system.