Investigation of Mechanical Deformation in Small-Scale Metallic Systems: Interfaces and Boundaries in Nano-pillars

California Institute Of Technology, Pasadena CA

Investigators

Abstract

TECHNICAL SUMMARY: It has been shown that in single crystals yield (and fracture) strengths increase in a power law fashion with sample size reduction once micron scale is reached, and therefore can no longer be inferred from bulk response or from literature. While these studies provide a powerful foundation for the fundamental deformation processes operating at small scales, they are a far reach from representing real materials used in structural applications, whose microstructure is often complex, containing boundaries and interfaces. Both homogeneous (i.e. grain and twin boundaries) and heterogeneous (i.e. phase and precipitate-matrix boundaries) interfaces in size-limited features are crucial elements in structural reliability of most modern materials. They are also of particular importance to damage initiation. Addressing these issues represents key thrust of this proposed research, where experimental and computational methods will be applied to obtain insight into mechanical behavior and microstructural evolution in small-scale metallic systems, whose deformation is governed by intricate interactions of defects with interfaces as well as with free surfaces. This proposal presents a unified plan combining unique nano-scale sample fabrication techniques with state-of-the-art in-situ mechanical testing capability, and site-specific TEM microscopy, further supported by computational efforts. The objective of this project is to develop a physical understanding of deformation mechanisms operating in small-scale (sub-micron) nano-pillars containing known interfaces and their ensuing mechanical properties. Attention will be focused on studying the following interfaces in individual nano-pillars: (1) multiple grain boundaries spanning the pillar volume (nanocrystalline Cu); (2) periodic in-grown twin boundaries in Cu (nano-twinned Cu); and (3) a combination of nano-grains and nano-twins in Cu (nanocrystalline nano-twinned Cu). Proposed study promises to also shed light on the relative role of intrinsic vs. extrinsic length scales on deformation mechanisms in metals, which will have a transformative impact in development of materials with unprecedented mechanical properties through architectural control. NON-TECHNICAL SUMMARY: Useful properties of structural materials are generally governed by their bulk microstructure. For centuries, improvements in structural materials relied heavily on processing, which in turn, dictated resulting microstructure and properties. As materials sciences are entering a revolutionary era, where specific material properties are attained through not only material but also architecture control of its constituents, often with sub-micron dimensions. In order to utilize these new principles, whose properties are dictated by combination of material microstructure and structure's architecture (rather than by bulk properties only) into structural applications, it is imperative to quantify the processes occurring at the interfaces upon mechanical loading. This proposal presents a unified plan combining unique nano-scale sample fabrication techniques with state-of-the-art in-situ mechanical testing capability, and microscopy, further supported by computational efforts. The objective of this project is to develop a physical understanding of deformation mechanisms operating in small-scale (sub-micron) metallic nano-pillars with controlled atomic arrangements and their ensuing mechanical properties. Gained knowledge promises to be essential for the development and improvement of structural materials, while training graduate and undergraduate students in an exciting interdisciplinary field that combines materials phenomena with integrated theoretical and experimental studies will help train a new generation of scientists.