The Property Of Co-based Bulk Metallic Glasses

Differential scanning calorimetry calorimeter (DSC),nanoindentation and synchro-tron radiation were used to study the thermodynamic and mechanic properties of CoTaBamorphous alloy．The research result of DSC showed that the crystallization at continuous heat underthe condition with different heat rate,the characteristic temperatures T_g,T_x,T_pofCo₅₆Ta₉B₃₅alloys moved toward to high temperature rang,which showed that the glassand crystallization transition have dynamic effects controlled by thermodynamic. Thecrystallization activation energy was calculated by the Kissinger and the Ozawa equation,the values were730.9and711.2kJ/mol respectively, the results showed that theamorphous alloys had a strong thermal stability and strong anti-crystallization ability. Thecalculation of local activation energy for crystallization indicated that the non-isothermalcrystallization became first increased and than decreased. Avrami exponent n showed thatthe nucleus growth mechanism changed from the interface-controlled growth to thediffusion–controlled growth.The indentation size effect and creep behaviour of Co₅₆Ta₉B₃₅amorphous alloy wereinvestigated by the technique of nanoindentation. The results showed that the amorphousalloy exhibited prominent serrated flow at low loading rate while the plastic deformationwas continuous at high loading rate. The relationship between hardness and indentationdepth showed significant indentation size effect. Creep rate sensitivity index(m) wascalculated from different loading rates, average value was6.9×10^-4, showed significantcreep resistance.The compression behavior of Co₅₄Ta₁₁B₃₅amorphous alloy was investigated atroom temperature in a dia-mond-anvil cell instrument using in-situ high pressure energydispersive X-ray diffraction with a synchrotron radiation source. The radial distributionfunction (RDF) and pair distribution function g(r) under high pressure were calculatedbased on the synchrotron radiation X-ray data via Fourier transformation. It was foundthat the structure of amorphous alloy was stable. Fractal theory further confirmed this conclusion. The equation of state of the bulk metallic glasses was determinated by fittingthe experimental data according to the Bridgman equation.