Internal friction of boride cermets at elevated temperatures

Abstract

Measurement of the damping of Fe-based cermets containing a boride hard phase (Mo 2FeB 2) was carried out using newly developed equipment of a torsion pendulum type under static tensile stress: high damping under the conditions of high temperature and high applied load was expected. Three kinds of boride cermets fabricated by Toyo-Kohan were used in this study. The composition of Mo 2FeB 2 type hard phase in Fe-based cermets was 66 vol.% for V30, 51 vol.% for V50 and 59 vol.% for C50. The damping capacity at 300 K for the strain amplitude of 7×10 −5 was ∼2% for every sample and increased with increasing temperature. The damping level tended to decrease with increasing tensile stress, but still remained at a high level at a tensile stress of 50 MPa. A high temperature relaxation peak appeared in the heating process for V30, V50 and C50. The activation energy of the high temperature peak was 84.8 kJ/mol for V30, 89.3 kJ/mol for V50 and 91.3 kJ/mol for C50. The relaxation mechanism of this peak is due to chromium atom diffusion caused by the phase transformation from martensite phase to austenite phase in Fe matrix phase.