Transmission electron microscopy–investigation of the microstructure of rapidly quenched Co80B20 alloys

Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and magneto-optical Kerr effect have been used to characterize different crystallization states of melt-spun Co80B20 alloys. The microstructures have been prepared by isothermal annealing at temperatures of TA=325–600 °C for different annealing times. Samples annealed for ta=30 min show an onset of the crystallization at annealing temperatures TA less than 325 °C with the primary precipitation of both face-centered-cubic Co and hexagonal close-packed Co embedded in the amorphous matrix. By HRTEM it is revealed that Co grains with ordered as well as highly distorted lattices are formed, whereby a characteristic feature of the latter are stacking faults. The following step is the formation of orthorombic Co3B with an average grain size of 7.6 μm and of nanocrystalline Co grains, whereby still some amorphous phase is present. Fully crystallized samples were obtained for annealing temperatures higher than 412 °C (...