Abstract:
Thermal and physical properties of glass-coated amorphous metal fibers have been investigated. It is demonstrated that an amorphous metal having a composition of Fe_{77.5}Si_{7.5}B_{15} undergoes a two-stage crystallization process when heated, and that the lower temperature crystallization can be completed without the higher temperature crystallization occurring. Scanning electron microscopy shows that such “Partial- Crystallization” creates a nanocrystalline, apparently interconnected structure within an amorphous matrix. The activation energy for the lower and upper temperature crystallizations have been calculated to be approximately 424 kJ/mol and 361 kJ/mol, respectively, using differential scanning calorimetry and Kissinger’s analysis. Crystallization temperature is heating rate dependant; at 10 ºC per minute, the two crystallizations occur at 540.5ºC and 550.5ºC respectively. Using a programmable dental furnace, a sample can be subjected to a heating curve and quenched in air, causing only the first crystallization to occur. The material so prepared is shown to have properties distinguished from the as-received material. The ultimate tensile strength of a partially crystallized fiber is measured to be 10-40% weaker than that of an as received sample. A core composition of Co_{68.15}Fe_{4.35}Si_{12.5}B_{16} has also been tested and has a single crystallization temperature (at 10ºC/min) of 552ºC with an activation energy of 503 kJ/mol. Using thermo-magneto-gravimetric analysis, Curie temperatures have been measured for the amorphous metal compositions; 426ºC for Fe_{77.5}Si_{7.5}B_{15}, and 319ºC for Co_{68.15}Fe_{4.35}Si_{12.5}B_{16}.
