Fundamental Understanding of Deformation Mechanisms in Nanocrystalline Superplasticity

这个建议的目的是获得一个基本的理解，在纳米晶材料的塑性变形机制。纳米结构的金属材料将通过几种加工方法来生产，包括高压扭转铸造材料，脉冲电沉积和金属玻璃结晶。在高温塑性过程中，晶粒间的沿着滑动是主要的流变特性之一。超细晶纳米晶材料包含非常大的界面密度，它们提供了一个独特的机会，研究晶界的结构状态及其在高温塑性晶界滑动的作用。 智力上的优点在于试图将微观结构信息与从这种纳米级材料中获得的力学数据在真正减小的长度尺度上的塑性上下文中关联起来。 特别强调的是，在真正的纳米尺度结构中，在基体内部产生晶内位错的困难，以及它对当前纳米晶塑性模型中的滑移调节过程的影响。该补助金将探讨所观察到的超塑性随晶粒尺寸减小而增加是否是一种普遍现象。提高超塑性应变速率将减少成形时间，并使其成为经济可行的工艺。降低超塑性成形温度将允许利用一些现有的成形技术用于工业上重要的金属间结构材料的车间实践。这些结果在形成具有复杂形状的传感器和器件方面具有重要的技术意义，这些传感器和器件可以受益于具有大的环境温度强度和硬度的纳米晶基体。

This proposal is designed to gain a fundamental understanding of the deformation mechanisms of plasticity in nanocrystalline materials. The nanostructured metallic materials will be produced by several processing methods that include high-pressure torsion of cast material, pulsed electrodeposition, and crystallization from metallic glass. The phenomenon of sliding along the grain interfaces is one of the dominant rheological characteristics in elevated temperature plasticity. The ultrafine-grained nanocrystalline materials contain a very large density of interfaces and they offer a unique opportunity to study the structural state of grain boundary and its role on grain boundary sliding in elevated temperature plasticity. The intellectual merit lies in attempting to correlate the microstructural information with the mechanical data obtained from such nanoscale materials in the context of plasticity in really diminished length scales. Special emphasis will be given to the difficulty of intragranular dislocation generation inside the matrix in truly nanoscale structure and its implication to slip accommodation processes in current models of nanocrystalline plasticity at elevated temperatures.The grant explores whether the observed increase in superplasticity with decreasing grain size is a general phenomenon or not. Increasing superplastic strain rate will decrease forming time and will make it an economically viable process. Lowering superplastic forming temperature will allow utilization of some of the existing forming technology for shop-floor practice in industrially significant intermetallic structural materials. The results are expected to be technologically significant in forming of sensors and devices with complex shapes that can benefit from the nanocrystalline matrix with large ambient temperature strength and hardness.