Study On Structural Evolution And Flow Behavior Of Amorphous Fe-Si-B Alloys

The structural evolution process of Fe-Si-B alloy from amorphous state to crystalline state has been investigated systematically using XRD, DSC, DIL, SEM, TEM, electrical resistivity tester, tensile stress annealing apparatus and microhardness tester. This paper emphasizes on the relaxation and properties of amorphous Fe₇₈Si₉B₁₃ alloy during low temperature annealing; the tensile flow, thermal expansion behavior and structural transition during higher temperature annealing; the primary crystallization contraction and the structural evolution process of amorphous Fe-Si-B alloys.As a typical one of Fe-based amorphous alloy, amorphous Fe₇₈Si₉B₁₃ alloy was annealed systematically at low temperature in present research. The tests of bend, HV, electrical resistivity, SEM and XRD on the as-quenched and annealed ribbons were performed respectively. The results show that the electrical resistivity of amorphous Fe₇₈Si₉B₁₃ alloy ribbon annealed during early, stage fluctuates regularly and the fluctuation tendency accords with that of hardness. Based on the analysis, the fluctuation is originated from the change of ordering degree in the alloy; during annealing at 200℃ to 300℃ for 15minutes to 15 hours, there appear ordered Fe₃Si and FeSi structures. The time of formation of FeSi structures is very close to the critical time of ductile-brittle transition, which means that there exists a close relation between the formation of FeSi structures and ductile-brittle transition; the formation of FeSi structures plays an important role in the transition and makes the alloy become another amorphous state.During higher temperature annealing, there occur more complex and severe structural changes in amorphous Fe-Si-B alloy due to the stronger movability of atoms in amorphous alloys. Meanwhile, the alloy will go through the glass transition and is faced with crystallization, so that, the changes of viscosity and thermal expansion become remarkable since they are sensitive to the atom movability. In present research, the tests of tensile flow and thermal expansion on the amorphous Fe₇₈Si₉B₁₃ alloy ribbon were performed during continuous heating process with different heating rates. The results show that there occurs a remarkable structural transition. Using the in-situ XRD, the transition was determined as nucleation of α-Fe.The results also show that the structural transition and crystallization as well as relaxation and the spontaneous volume magnetostriction at low temperature are...