Room Temperature Microplasticity and High Temperature Internal Friction of Mo₂FeB₂ Based Hard Alloys

Abstract

Influence of strain amplitude and temperature on the internal friction of Mo₂FeB₂ based hard alloys were measured by torsional vibration method. The strain amplitude dependency of internal friction was observed. It became clear from the study about Granato-Lücke plots that the mechanism of this relaxation is attributed to break away model of dislocation. It was observed that microplasticity at room temperature appeared in order of C70(Mo₂FeB₂-54%iron based binder(10%Cr, 5%Ni)), V31(Mo2FeB2-34%iron based binder(6%Cr, 6%Ni)), H71(Mo₂FeB₂-54%iron based binder(17%Cr, 19%Ni)). In the temperature dependency of internal friction of the hard alloys containing martensite phase in the bonding phase, relaxation peak caused by the phase transformation from austenite phase to martensite phase was appeared at 1033-1068 K and its activation energy and phase transformation temperature were 140-145 kJ/mol and 1093-1173 K, respectively. At following high temperature, a conspicuous increase of the internal friction probably based on plastic flow of the grain boundary was observed. Its activation energy was 106-218 kJ/mol.