Plate-like precipitate effects on plasticity of Al-Cu alloys at micrometer to submicrometer scales

TL;DR

This study investigates how plate-like $ heta^ extprime$-Al$_2$Cu precipitates influence the strength, plastic fluctuations, and deformation mechanisms of Al-Cu alloys at micrometer to submicrometer scales, revealing size-dependent effects on plasticity and stability.

Contribution

It provides new insights into the size-dependent effects of plate-like precipitates on plasticity and stability in Al-Cu alloys at small scales, combining experimental and theoretical analysis.

Findings

Precipitates strengthen materials and suppress fluctuations at larger scales (≥3 μm).

Breakdown of pinning landscape at smaller scales reduces suppression of intermittency.

Enhanced strain hardening and reduced jerkiness occur at intermediate sizes with precipitate shearing.

Abstract

The continuous miniaturization of modern electromechanical systems calls for a comprehensive understanding of the mechanical properties of metallic materials specific to micrometer and sub-micrometer scales. At these scales, the nature of dislocation-mediated plasticity changes radically: sub-micrometer metallic samples exhibit high yield strengths, however accompanied by detrimental intermittent strain fluctuations compromising forming processes and endangering structural stability. In this paper, we studied the effects of plate-like $\theta^\prime$-Al$_2$Cu precipitates on the strength, plastic fluctuations and deformation mechanisms of Al-Cu alloys from micro-pillar compression testing. The plate-like precipitates have diameters commensurate with the external size of the Al-Cu micro-pillars. Our results show that these plate-like precipitates can strengthen the materials and suppress plastic fluctuations efficiently at large sample sizes ($\geq 3 \mu m$). However, the breakdown of the mean-field pinning landscape at smaller scales weakens its taming effect on intermittency. Over an intermediate range of sample sizes allowing the precipitates to cross the entire pillar, an enhanced apparent strain hardening and a sharp decrease of jerkiness are observed, in association with the presence of {100}-slip traces along the coherent $\theta^\prime$-Al$_2$Cu precipitate/$\alpha$-Al matrix interface and precipitate shearing. These complex effects of plate-like precipitates on plasticity are analyzed, experimentally and theoretically, in view of the interferences between external and internal sizes, and the related modifications of the underlying plastic mechanisms.