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

• Published in: Materials & Design 2020-03, Vol.188, p.108444, Article 108444
• Main Authors: Zhang, Peng, Bian, Jian-Jun, Zhang, Jin-Yu, Liu, Gang, Weiss, Jérôme, Sun, Jun
• Format: Article
• Language: English
• Subjects: Condensed Matter; Dislocation dynamics; Materials Science; Physics; Plastic fluctuations; Size effects
• ISSN: 0264-1275; 0261-3069; 1873-4197; 0264-1275
• DOI: 10.1016/j.matdes.2019.108444

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 endangering structural stability. In this paper, we studied the effects of plate-like θ′-Al2Cu precipitates on the strength and plastic fluctuations of Al-Cu alloys from micro-pillar compression testing. The particularity of our samples is that 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 through the Orowan mechanism at large sample size. However, the breakdown of the mean-field pinning landscape weakens its suppression effect on plastic intermittency. On the other hand, the plastic intermittency can be inhibited efficiently at small sample size by using the plate-like θ′-Al2Cu precipitates penetrating the entire micro-pillar, in association with the presence of {100}-slip traces along the coherent precipitate/Al matrix interface and enhanced strain isotropy. Besides these experimental observations, we also aim to extract the laws common in different Al alloys, and address the specific plastic mechanisms for Al-Cu micro-crystals. [Display omitted] •Different structures are constructed in Al-Cu pillars by adjusting the ratio of sample and plate-like precipitate diameters.•A complex sample size dependent plasticity is observed, showing three distinct regimes.•The intermittent plasticity can be effectively inhibited when the plate-shaped precipitates penetrate the entire sample.•The relation between power-law exponent of strain burst distribution and wildness is universal.