快速凝固AlNiCuNd金属玻璃在纳米尺度上的初始晶化行为

Primary Crystallization Behaviour of Rapidly SolidifiedAl-Ni-Cu-Nd Metallic Glass on Nanometer Scale

采用熔体旋甩法制备了快速凝固Al87Ni7Cu3Nd3金属玻璃,并以等温加热和非等温加热模式处理试样。采用差示扫描量热分析、X射线衍射分析、配有选区电子衍射的高分辨电镜分析等测试手段,研究了富Al非晶合金的晶化过程及其部分晶化的微观结构。研究结果表明:快淬态薄带在微观下完全呈非晶态且分布均匀,但也包含高密度的淬态丛聚或晶籽;快速凝固Al87Ni7Cu3Nd3合金薄带在初始晶化期间从非晶基体中析出的主要是α Al纳米晶体颗粒。基于初始晶化的部分退火薄带显微组织特征可以描述为:大量的α Al晶体纳米颗粒均匀弥散分布在残余非晶基体中,α Al晶体颗粒大多处于相互独立的状态,且呈随机自由取向,但当加热温度太高时,可能会有少量Al3Ni细小颗粒出现;α Al晶体从非晶中析出是一个包括形核长大的完整过程,在初始晶化初期,α Al晶体颗粒以极高的速率析出,由于溶质(Ni和Nd等)浓度扩散场所引起的软钉扎作用,α Al晶体颗粒生长受阻,甚至在后期残留非晶相出现稳定化,初始晶化变得困难;在初始晶化过程中,阻碍α Al晶体生长的主导动力学机制是软钉扎,而不是几何钉扎。

Rapidly solidified Al_(87)Ni_7Cu_3Nd_3 metallic glass ribbons were prepared by using melt spinning, and were treated under both continuous heating and isothermal heating regime. Crystallization behavior of Al-rich metallic glass and its partial crystallized microstructural characteristics were examined by means of differential scanning calorimetric, conventional X-ray diffraction and high resolution transmission electron microscopy with selected-area electron diffraction. The results show that the rapidly solidified metallic glass ribbons are fully amorphous and homogeneous in the micron scale, but contain high density of quenched-in clusters or crystallite embryos. Main precipitates from the amorphous matrix are α-Al crystal nanometer particles during primary crystallization. Microstructures of the partially annealed ribbons, based on primary crystalliza-(tion,) can be characterized as high number density of α-Al crystal nanometer particles disperseuniformly in an amorphous matrix, and the α-Al crystal particles are in an isolate state, separatedwith each other, with random orientation. But when the crystallizing temperature is too high, perhaps a minor amount of fine Al_3Ni particles appear. Precipitation of α-Al nanocrystalline particles from the amorphous matrix is an integrated process of nucleation and growth. At the earlier stage of primary crystallization, the α-Al crystal particles precipitate at a very fast rate. With evolution of transformation, the growth of α-Al crystal particles is retarded due to soft impingement effect caused by concentration diffusion field of nickel or neodymium solute atoms. (Even) at the later stage the residual amorphous phase becomes so thermally stable that the primary crystallization is difficult to continue occurring.