Basic Process Principle Of Fabricating Metallic Glasses Fibers Through Melt Extraction Technique

Metallic glass fibers of Co_68.25Fe_4.25Si_12.25B_15.25 and Fe_73.5Si_13.5B₉Nb₃Cu₁ alloys were prepared through Melt Extraction Technique (MET) in this dissertation. Based on MET, the mathematic model of the extraction process was founded and the fundamental principle was discussed.Differential Thermal Analysis (DTA) result with a continuous heating rate of 0.67K/s, shows that there are obvious crystallization peaks in both fibers. The starting temperature of the first and second crystallization peaks of Co_68.25Fe_4.25Si_12.25B_15.25 alloy are 829.2K and 915K, respectively; and those of Fe_73.5Si_13.5B₉Nb₃Cu₁ alloy are 802.6K and 951.2K respectively. It indicates clearly that the matrix structure of fibers is amorphous.By increasing the rotating speed of the wheel from 2400r/min to 2700r/min, the average diameter for Fe-based fibers decreases from 72.2μm to 50.9μm, implies the trend of decreased in diameter connected with higher extracting speed of fibers. The diameters of Co-based fibers increased sharply and the fasciation may be resulted in when the feeding speed of the melt increased from 0.1mm/s to 0.3mm/s, shows that the diameters of fibers is sensitively related with the feeding speed of the melt. By increasing the temperature of the melt, the diameter of the fiber could be reduced and the roundness could be improved as well, however, the degree of amorphism of the fiber may be deteriorated by high temperature.The average length is 75mm for Co-based fibers, and 110mm for that of Fe-based, the maximum length is 100mm for Co-based fibers, and 150mm for Fe-based. It is considered that the extracting velocity and the surface fluctuation of the melt are the two main factors that controlling the available length of the fibers, so the continuity of fibers related with material characteristic, process technique, as well as the conditions of the equipment.Based on the Energy Conversation Principle and Mass Conversation Principle, the macro-model for the fiber forming during the extracting of the melt was founded, according to the characters of the movement of the melt during extracting. And it is simulated by Matlab7.0 software for the influence and relationship of the extracting velocity, embed depth and other parameters to the fiber's diameter. The results are consistent well with experiments. Moreover, the results shows that the process parameters during the extracting couple each other, and a parameters space correspond to that of a predefined fiber diameter, in which the process parameters can be easily selected, the predefined fiber diameters can be attained.It is showed by SEM that the surface deficiencies of fibers include kink, fin, crack, denudation, enclosed mass, Rayleigh wave and cross-section concave. The evenness of fibers is caused to be changing periodically by Rayleigh waves, which is resulted from the gathering of the extracted melt when it is not solidified in time as it ascends with wheel. The concave of the cross-section is resulted from the contact face remained between wheel and melt, which may debase the roundness of fibers.