摘要:
从非晶合金的微观结构出发,基于处理强无序和具有随机几何结构系统常用的理论方法——逾渗理论来描述非晶合金剪切屈服时的塑性流变.为了更好地理解非晶合金剪切带萌生时的临界问题,结合已有的“自由体积(free volume)模型”和“剪切转变区(shear transformation zone)模型”,建立了非晶合金剪切转变的逾渗模型.以Cu25Zr75二元非晶合金为例,计算了在剪切转变区内易发生塑性流动的原子团簇剪切失稳的逾渗阈值,并粗略估算了这些原子团簇的大小.研究发现,剪切失稳的逾渗阈值与临界约化自由体积浓度(xc～2.4％)有着相似的特性,不同之处在于其值与自由体积的分散度有着密切联系.研究结果作为非晶合金的韧脆转变问题提供了新思路.
Abstract:
According to the microstructure of amorphous crystal,the percolation theory,which is a theoretical approach to dealing with the inhomogeneous physical systems or random fractals,is used to describe the plastic flows of amorphous alloys under shear yielding.In order to understand in depth the critical problems about the shear band initiations in amorphous alloys,a percolation model for shear transformations of these alloys is established by combining with the existing free volume model and shear transformation zone model.Taking the binary amorphous alloy Cu25Zr75 for example,the percolation threshold for the shearing instability of the atomic clusters prone to producing plastic flows in the shear transformation zone is calculated when a shear band comes into being.In addition,the size of the abovementioned cluster is also roughly estimated.The calculated results show that the percolation threshold of the shearing instability is similar to the critical reduced free volume value (xC) of ～ 2.4％ for the onset of yielding in amorphous alloy although this threshold is closely related to the dispersity of free volume.The present study may provide a new idea and method of studying the ductile-brittle transition in amorphous alloy.
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