微纳米金属玻璃的高速加热超塑性成型与力学行为

Small scale (micro- and nano-scale) metallic glasses (SMG) have attracted extensive attention in the past ten years. Novel mechanical behavior of SMGs has been reported controversially because of preparation and/or testing problems. At the same time, the mechanism and structure origin of such behavior have not been explained either experimentally or theoretically, even though some phenomenon model was proposed. Our previous works have some preliminary results on such issues. Firstly, we will revise our metallic glassy wire preparation equipment to produce high-quality SMGs of various composition systems by introducing capacitor-discharge technique. Based on this, we will unravel the mechanism of superplastic forming of SMGs. Secondly, we will do instrumentation to characterize tensile and relaxation behavior of SMGs without extrinsic effects. Structure evolution during tension will also be investigated to unravel structure origin of mechanical behavior of SMGs. Finally, constitutive equation for depicting deformation of SMGs will be established by modeling coupling of shear transformation at aboriginal free volume and shear dilatation to unravel correlation between deformation behavior and structure evolution of SMGs. The project has implications for understanding fundamentals of superplastic forming and deformation behavior of SMGs and their application in micro- and nano-devices.

微纳米金属玻璃在过去十年里受到了人们广泛关注。其新奇力学行为被报导，这些报导因为样品制备和表征手段问题而存在争议。虽然有唯象模型试图解释微纳米金属玻璃的力学行为，但其物理机制和结构起源没有得到很好的解释。项目申请人在这些方面做了一些初步工作。我们将改进之前的微纳米金属玻璃超塑性成型设备，引入电容放电技术，用高速加热法制备高质量多成分体系的微纳米金属玻璃。在此基础上认清微纳米金属玻璃的超塑性成型机理。然后，我们将研制表征微纳米金属玻璃拉伸力学行为和弛豫行为的设备以去除外界因素的影响。我们也将表征拉伸过程中微纳米金属玻璃的结构演变以揭示形变的结构起源。最后，我们将模型化样品中原有自由体积的剪切转变与剪涨区域的剪切转变之间的耦合作用，建立微纳米金属玻璃流变本构方程以揭示其流变与结构演化的关联。本项目将帮助理解微纳米金属玻璃超塑性成型机理与流变的物理起源，为其走向微纳米器件中的应用奠定基础。

本项目主要研制了的快速加热金属玻璃丝制备设备和工艺。该设备采用精密钨灯丝对金属玻璃母体进行加热，并用LabVIEW控对对钨灯丝的电源Agilent E3642A进行编程控制，精确控制加热过程。当金属玻璃母体被加热到其过冷液相区的时候，被下面的砝码拉制成微纳米尺度的金属玻璃丝。在上述设备研发的基础上还探索空心微纳米金属玻璃丝的制备工艺，成功制备单孔和多空微纳米尺度金属玻璃丝，并对金属玻璃丝进行了非均匀结构表征。表征结果表明金属玻璃管的表面密度较低。理论研究表明表面的低密度区是由金属玻璃丝在拉制成型过程中，过冷液体表面张力的作用引入的自由体积造成的。管壁中的密度也是非均匀的其中的高密度区在沿着金属玻璃丝拉制的方向被拉长。说明过冷液体和固体金属玻璃一样也是密度不均匀的，这种非均匀结构在成型过程中被拉长而且被冻结下来。同时理论分析也说明，金属玻璃丝是从母体中一层一层的抽拉出来的。