Deformation Behavior Of Amorphous Fe₇₈Si₉B₁₃ Alloy And Fe₇₈Si₉B₁₃/Ni Laminated Composite

Amorphous Fe₇₈Si₉B₁₃ alloy found in 1970s is metastable material. Itsexcellent magnetic properties and low cost attract extensive attention. Thismaterial has a range of desirable magnetic properties such as high magneticpermeability, low coercive force, low core loss and good frequency dispersiveproperties and is so far recognized as the best combination properties of softmagnetic material. Over the last twenty years, most studies have been focused onthe oxidation behavior, the effect of crystallization behavior on magneticproperties, crystallization products and their microstructure, the embrittlementcaused by crystallization and high-temperature viscosity of amorphousFe₇₈Si₉B₁₃ alloy. However, the investigation on the fracture behavior at roomtemperature, the deformation behavior at high temperature and improved theductility of amorphous Fe₇₈Si₉B₁₃ alloy was few reported. At ambienttemperature plastic deformation in amorphous alloys occurs by the localizedshear bands which led to catastrophic failure. The low plasticity constraintsamorphous alloys used as structural materials.Thus the study and development ofamorphous alloys have been focused on increasing the plasticity and toughnessof amorphous alloys.To improve the ductility and used thickness of amorphousFe₇₈Si₉B₁₃ ribbon, Ni/Fe₇₈Si₉B₁₃ laminated composite was prepared in this paper.The stress relaxation forming of amorphous Fe₇₈Si₉B₁₃ ribbon well belowits crystallization temperature (TBxB=540℃) was investigated. The effects oftemperature, time and pre-annealing on stress relaxation behavior were studied.The stress relaxation phenomenon could be explained by the Free Volume Model.The variation of the microstructure and microhardness during stress relaxationforming process was studied using X-ray diffraction (XRD), atomic forcemicroscopy (AFM), transmission electron microscopy (TEM) and Vickersmicrohardness test, respectively. FeSi andα-Fe nanocrystalline phases appearwhen amorphous Fe₇₈Si₉B₁₃ ribbons were relaxed at 300℃.The specimensnanocrystallized partially under temperature and stress well below TBxB. Due tonanocrystals embedded in the amorphous matrix, the microhardness of therelaxed specimens greatly increased in contrast with the as-quenched state. The irreversible viscous flow contribution and reversible anelastic strain contributionwere separately described by simple experiments and could be reasonablyexplained according to topological short-range ordering (TSRO) and chemicalshort-range ordering (CSRO).The tensile fracture morphology of amorphous Fe₇₈Si₉B₁₃ Bribbon at roomtemperature was observed by SEM. The effects of specimen size and tensilevelocity on facture morphology were also studied. The fracture mechanism ofamorphous Fe₇₈Si₉B₁₃ Bribbon could be understood in terms of the ellipse criterion.The fracture surface consists of mirror, mist and river-pattern zones with crackpropagating. The formation of nanoscale damage cavity structure is a maincharacteristic morphology in all the fracture regions. The nanoscale periodiccorrugation patterns are formed in the mirron region by the self-assembly of thedamage, which wavelength is about 150nm. No effect of specimen size andtensile velocity on the wavelength size.Uniaxial tensile tests were carried out in the temperature range of430℃⁵30℃and at a strain rate of 8.33×10P-4PsP-1P to evaluate the plasticdeformation of amorphous Fe₇₈Si₉B₁₃ Bribbon. The microstructure of specimensafter tension was studied by XRD and SEM. The maximum elongation of 36.3%is obtained at 500℃, exhibiting the good high-temperature defomation ofamorphous Fe₇₈Si₉B₁₃ Bribbon. The suitable gas pressure bulging conditions forthe specimens are 500℃, 3.4MPa and 30min. Under the conditions, the relativebulging height (RBH) of 0.45 is obtained. The thickness distribution of bulgedspecimens is uniform.Fe₇₈Si₉B₁₃/Ni laminated composite was prepared in the form of three-ply(Ni-Fe₇₈Si₉B₁₃-Ni) laminated structure by electrodeposition method. The averagegrain size of Ni layers is about 50nm. The interface of laminated composite wasinvestigated by SEM equipped with energy dispersive scanning (EDS) and lineanalysis techique. The laminated composite has a good interfacial bondingbetween amorphous layer and nano-Ni layers due to the mutual diffusion ofatoms in Fe₇₈Si₉B₁₃ and Ni layers during the process of electrodeposition. Thelaminated composite possesses a very high tensile strength (2090MPa) andreasonable tensile elongation (8.5%), which is well larger than that of monolithicamorphous Fe₇₈Si₉B₁₃ ribbon (1.39%). The aim of enhancing the plasticity of amorphous ribbon by producing laminated composite is gained.The effects of temperature, initial strain rate and volume fraction of nano-Nilayer on tensile properties of Fe₇₈Si₉B₁₃/Ni laminated composite were studied.The elongation of 115.5% was obtained at 450℃and at an initial strain rate of8.33×10P-4PsP-1P containing VBNiB=0.77, which is greatly higher than that of monolithicamorphous Fe₇₈Si₉B₁₃ ribbon (36.3%). Bulging tests were carried out to evaluatethe plastic forming properties of Fe₇₈Si₉B₁₃/Ni laminated composite. Under theconditions of 450℃, 4MPa and 30min, good bulging part with RBH of 0.4 wasobtained.