High Temperature Mechanical Properties of Ti(C, N)-Mo₂C-Ni Cermets Studied by Internal Friction Measurements

Abstract
internal friction measurements were performed on TiC_0.7N_0.3Mo₂C-Ni metal-bonded refractory materials, in order to study how the composition and the microstructure of cermets control the mechanical properties of these materials. A free inverted torsion-pendulum was used, oscillating in the 0.2-2 Hz frequency range, up to 1273K. Isothermal I.F. spectra were measured in a forced torsion-pendulum in the 10-10^-4 Hz range, and up to 1400K. One thermally activated IF. peak at 1100K (at 0.5Hz), is superimposed with a high temperature I.F. background. The amplitude of the background and the activation energy of the peak are strongly dependent on the Mo and C content in the material. Transmission 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 1100K peak is attributed to the dragging of Mo atoms by dislocations in Ni-Mo-Ti alloy, while the high temperature background is associated with long distance displacements of dislocations in this binder phase. The refractory skeleton gives a contribution to the high temperature background, and to another peak at 900K. A comparison is made with I.F. measurements in WC-Co, that confirms the specific role of the metallic phase for each system.