Fundamental Understanding of Deformation Mechanisms in Nanocrystalline Superplasticity

University Of California-Davis, Davis CA

Investigators

Abstract

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.