Crystallization of the metallic glass Fe78B13Si9

The microstructures and kinetics with heating for an amorphous Fe₇₈B₁₃Si₉ alloy were studied by X-ray diffraction, transmission electron microscopy, differential thermal analysis and differential scanning calorimetry. The first crystallization takes place by the simultaneous formation of -(Fe,Si) and Fe₃B having the shapes of dendrite and spherulite, respectively. Metastable Fe₃B then transformed into a stable phase of Fe₂B at a higher temperature. The activation energy for crystallization and the Avrami exponent were determined. It was found that crystallization behaviour in Fe₇₈B₁₃Si₉ is controlled by nucleation rather than growth.     

Viscous behaviour and glass formation in Fe78B13Si9 amorphous alloy

Using a rotational viscometer, the viscosity of molten Fe₇₈B₁₃Si₉ alloy was measured over the temperature range 1165–1350 °C. The temperature dependence of the viscosity of liquid alloy is adequately described by the Arrhenius equation. However, this expression cannot be directly extended to the undercooled liquid temperature region. In this paper a proper equation derived from the free volume theory is proposed to describe the viscosity-temperature behaviour of Fe₇₈B₁₃Si₉ alloy in the temperature range of the undercooled liquid and above its melting point. Furthermore, the isothermal time-temperature-transformation curve for crystallization is constructed based on the assumption of homogeneous nucleation and crystal growth, together with the temperature dependence of the viscosity. The critical cooling rate required to form a glass of Fe₇₈B₁₃Si₉ alloy was calculated to be approximately 10⁵° Cs^–1.     

非晶Fe78Si9B13合金结构对磁性的影响

研究了普通退火对非晶Fe78Si9B13合金磁性能和结构的影响.实验发现:经不同温度退火1h后,试样的静态磁性能在Ta=390℃呈现最佳值;损耗则在Ta=440℃呈现最低值;在Ta=440℃经不同时间退火后,试样在ta=2h呈现横向感生磁各向异性.由退火后试样的初始磁导率与温度的关系及磁致伸缩系数的变化结果表明,当有极少量的α-Fe(Si)晶体相析出时,可明显改善合金的动态磁性能;当α-Fe(Si)晶体相进一步析出时,可使合金呈现良好的恒导磁特性.     

恒电感非晶Fe78 Si9B13合金铁芯的研究

研究了普通退火对非晶Fe78Si9B13合金铁芯电感的影响.实验发现在不同退火温度(450～490℃)非晶合金铁芯的电感均随退火时间的延长单调下降;退火温度越低,电感下降的速率越小.合金经480℃×60min退火,有适当数量的α-Fe(Si)晶体相析出后,可呈现良好的恒导磁特性,形成横向感生磁各向异性;非晶合金铁芯具有较低的电感,很强的抗直流偏磁场能力和良好的恒电感特性.     

非晶Fe78Si9B13磁粉芯的制备及性能研究

以气流磨法制备的Fe78Si9B13非晶粉末为原料成功制备了非晶磁粉芯。研究了退火温度和成型压力对磁粉芯性能的影响规律。结果表明,在低于起始晶化温度的条件下,非晶磁粉芯的损耗随退火温度的提高而先降低后增大,磁导率变化规律则相反,并在350℃时到达最佳值;成型压力增大导致磁粉芯的密度提高,对应的损耗降低,导磁率增大,并在2000MPa左右达到最大值。     

Fe78Si9B13非晶合金磁芯封装及其软磁性能

研究了Fe78Si9B13非晶合金磁芯进行环氧封装及封装后对非晶合金磁芯软磁性能的影响。结果表明对磁芯进行环氧封装,有效改善磁芯的机械强度同时,能改善带材表面的平整度,在带材表面形成一层绝缘层,显著降低了非晶合金磁芯高频下的损耗值,封装后的非晶合金磁芯在Bm=1T,f=1kHz下,损耗值比封装前下降了14%。综合考虑机械强度大小、磁化难易、损耗高低等因素,封装胶浓度为2%时封装效果最佳。     

Crystallization of (Fe, Co)78Si9B13 alloys: influence of relaxation processes

Crystallization of Fe78-xCoxSi9B13 amorphous alloys has been studied by differential scanning calorimetry (DSC), thermomagnetic gravimetry and X-ray diffraction techniques. Thermal stability of the amorphous alloy monotonically decreases with increasing cobalt content. The devitrification process as detected by DSC occurs in two main stages partially overlapping in temperature, but magnetic characterization reveals a third stage for cobalt-rich alloys. Primary precipitation of -(Fe, Co) is followed by a polymorphic reaction to give (Fe, Co)2B phase. Fe3B-type phase is also detected at the end of the first crystallization stage for iron-rich alloys and -Co(Si) and Co2B phases are found in fully crystallized samples for x=60. The influence of relaxation processes on the crystallization was investigated, but no significant effects of pre-annealing on the crystallization parameters resulted. © 1998 Chapman & Hall     

非晶Fe_(78)Si_9B_(13)合金磁致低温纳米晶化的超精细结构研究

用低频脉冲磁场处理了非晶Fe78Si9B13合金,以红外非接触测温仪测量处理过程的温升,用Mssbauer谱、XRD和TEM等手段观察样品的超精细结构变化。结果表明,脉冲磁场处理过程中,非晶Fe78Si9B13合金发生了低温纳米晶化,试样温升均7℃,晶化析出相仅为α-Fe(Si),晶粒尺寸约为10nm,析出量为2.428%～6.992%,所形成的非晶-纳米晶双相合金的平均超精细磁场较原始非晶发生了明显变化,其单峰向低位场移动,在高位场又有出现另一单峰的迹象,脉冲处理参数不同,各峰出现的位置不同。     

Crystallization of amorphous Fe73.5Si13.5B9Nb3Cu1

A study is reported on the devitrification behaviour of the amorphous alloy Fe73.5Si13.5B9Nb3Cu1. Samples of the studied glass underwent isothermal and non-isothermal heat treatments in a thermal analysis apparatus. In addition some samples were very rapidly heated to very high temperatures by means of a laser beam. In this way a large temperature range was explored and information was obtained on the overall thermal evolution of the studied amorphous alloy. The experimental results suggest that, as recently proposed in the literature, nanocrystallization can be linked to a rate limiting Nb diffusion stage in the crystal growth process. However topological short range ordering (TSRO) and chemical short range ordering (CSRO) also affect the devitrification behaviour. In the case of the studied alloy, three temperature ranges can be defined. At low temperature only TSRO occurs. Above a temperature that lies approximately in the range 450–500°C, glass in glass phase separation occurs up to a temperature that lies approximately in the range 700–750°C, above which it appears to be very limited. The occurrence of glass in glass phase separation appears to be necessary to obtain a fine microstructure, because Nb concentrates in the boron depleted, iron rich glassy phase. The occurrence of TSRO prior to demixing should be avoided if nanocrystallization is desired. All this appears to be satisfied by isothermally treating the sample at a temperature of 555°C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of pre-annealing or pre-cold-working treatments on the structural evolution of Fe78B13Si9 amorphous alloys

The effects of pre-annealing or pre-cold-working treatments on the structural modifications occurring during the heating of an Fe₇₈B₁₃Si₉ amorphous alloy are reported. Structural relaxation and crystallization stages were investigated with the help of internal friction measurements, Mössbauer spectroscopy and transmission electron microscopy. It is shown that pre-annealing involves atomic reorganizations, the effects of which are more obvious on the relaxation stage than on the crystallization one. Moreover, pre-cold-working implies atomic disturbances which modify the structural relaxation as well as the crystallization stage. The results are explained on the basis of the atomic structure of the amorphous alloy, consisting of atoms clusters, the characteristics of which are responsible for the observed phenomena.     

Effects of annealing on magnetic properties of Fe78B13Si9

We have annealed amorphous Fe₇₈B₁₃Si₉ samples at temperaturesT _a = 355 to 460 ° C for timet _a = 10 to 60 min, in an atmosphere with purging of nitrogen gas. After thermal treatment, we examined the hysteresis loop, DSC curve, and the X-ray diffractogram of each sample. The coercivityH _c, the peak inductionB _max, and the lossW _h were analysed to study the affects of annealing. Stress-relief and partial crystallization are two important parameters in determining optimal annealing conditions.     

低频脉冲磁场处理非晶Fe78Si9B13合金纳米晶化的DSC研究

用低频脉冲磁场处理非晶Fe78Si9B13合金,采用差示扫描热分析(DSC)的方法测定了不同升温速率下非晶Fe78Si9B13合金的DSC曲线,利用Kissinger方程计算出了晶化过程的激活能.结果表明,晶化激活能由处理前的433.6kJ/mol降到200kJ/mol以下,提高了晶核形核速率,抑制了晶核长大速率,从而实现了非晶合金的低温纳米晶化.     

非晶合金Fe78Si9B13的纳米晶化及电阻研究

采用QJ36型单双臂两用电桥四点接触法对脉冲磁场处理后的非晶合金Fe78Si9B13试样的比电阻进行了研究。实验结果表明，脉冲磁场处理后试样的比电阻与磁场强度存在一极小值关系，并出现电阻反常现象(在一定参数下电阻升高)；比电阻随磁场频率增加而呈非单调减小。由电子显微镜分析可知，脉冲磁场处理可使非晶合金Fe78Si9B13发生纳米晶化，由此可知电阻反常现象是试样纳米晶化的结果。