Fe_(73.5)Si_(13.5-x)Ge_xB_9Cu_1Nb_3(x=3,6)非晶合金的结晶动力学

Crystallization Kinetics of Amorphous Alloys Fe_(73.5)Si_(13.5-x)Ge_xB_9Cu_1Nb_3(x=3, 6)

用标准单辊甩带技术在大气环境下制备Fe73.5Si13.5-x Gex B9Cu1Nb3(x=3,6)非晶条带,分别在470℃、510℃、550℃和590℃对非晶条带进行真空等温退火1 h后,在非晶基体中形成了纳米晶相。用X射线衍射(XRD),透射电镜(TEM)和差示扫描量热法(DSC)测量研究了快淬态和热处理后样品的结构和结晶动力学。基于差热分析的数据,使用Kissinger,Ozawa和AugisBennett模型计算了非晶条带的结晶激活能,利用Johnson-Mehl-Avrami(JMA)方程计算了非晶条带初始结晶的局域Avrami因子n。局域Avrami因子n随晶化体积分数α的显著变化说明,非晶条带非等温初始结晶的机理在不同的晶化阶段是不同的。晶化初期的机理是扩散控制的三维形核和晶粒生长的整体晶化,形核速率逐渐减小;晶化中后期为一维形核和生长的表面晶化过程,形核速率近似为零。基于XRD和TEM测量结果,分别在510℃、550℃和590℃真空等温退火1 h后,在Fe73.5Si13.5-x Gex B9Cu1Nb3(x=3,6)非晶条带中析出的α-Fe(Si,Ge)相的平均晶粒尺寸D小于15 nm。

Amorphous ribbons Fe73.5Si13.5-xGexB9Cu1Nb3（x=3,6） were prepared by a normal single copper wheel melt spinning technique in atmosphere, which then were isothermally annealed at 470℃, 510℃, 550℃ and 590℃ respectively for 1 h in a vacuum furnace. The microstructure and crystallization kinetics of the ribbons were characterized by means of X-ray diffraction （XRD）, transmission electron mi- croscopy （TEM） and differential scanning calorimeter （DSC） measurements. While the crystallization acti- vation energies of amorphous ribbons were calculated by using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The local Avrami exponent n for primary crystalliza- tion was calculated by using Johnson-MehI-Avrami （JMA） equation. The significant variation of local Avra- mi exponent n with crystallization volume fraction a demonstrated that the primary crystallization kinetics of amorphous ribbons varied at different stages. In the initial stage, the crystallization mechanism was diffusion controlled bulk crystallization with three dimensional nucleation and grain growth, while the nucleation rate deceased with time. In the following stage, it was surface crystallization with one dimensional nucleation and grain growth, while the nucleation rate was near zero. The average sizes D of α-Fe （Si, Ge） grains for the samples annealed at 510℃, 550℃ and 590℃ for 1 h in a vacuum furnace were less than 15 nm as confirmed both by XRD and TEM measurements.