Rotatable precipitates change the scale-free to scale dependent statistics in compressed Ti nano-pillars

Abstract

Compressed nano-pillars crackle from moving dislocations, which reduces plastic stability. Crackling noise is characterized by stress drops or strain bursts, which scale over a large region of sizes leading to power law statistics. Here we report that this “classic” behaviour is not valid in Ti-based nanopillars for a counterintuitive reason: we tailor precipitates inside the nano-pillar, which “regulate” the flux of dislocations. It is not because the nano-pillars become too small to sustain large dislocation movements, the effect is hence independent of size. Our precipitates act as “rotors”: local stress initiates the rotation of inclusions, which reduces the stress amplitudes dramatically. The size distribution of stress drops simultaneously changes from power law to exponential. Rotors act like revolving doors limiting the number of passing dislocations. Hence each collapse becomes weak. We present experimental evidence for Ti-based nano-pillars (diameters between 300 nm and 2 μm) with power law distributions of crackling noise P( s ) ∼ s − τ with τ ∼ 2 in the defect free or non-rotatable precipitate states. Rotors change the size distribution to P( s ) ∼ exp(− s / s 0 ). Rotors are inclusions of ω-phase that aligns under stress along slip planes and limit dislocation glide to small distances with high nucleation rates. This opens new ways to make nano-pillars more stable.

Plastic yielding and deformation bursts in the presence of disorder from coherent precipitates

“…1 [35]). One may notice that this size scale is close to typical micropillar experiments [9,12,15,23], but here the use of periodic boundaries implies that we are simulating a part of a bulk system. A total of 24 initial dislocations in the slip system 1 2 110 {111} imply an initial dislocation density ρ 0 ≈ 2.0 × 10 12 m −2 .…”

“…These considerations then lead us to the question of how one may, by controlling the precipitate content of a 3D crystal, tune its mechanical properties [12,14,23] and how that relates to the statistical physics aspects-relaxation, burst size distributions-for a given precipitate microstructure. Previous studies [24][25][26][27] have addressed the problem of individual dislocations interacting with precipitates.…”

Fluctuations in crystalline plasticity

“…Studies revealed a much weaker size effect on strength in alloys compared with pure materials. This was interpreted as the fingerprint of a tailored internal length scale, which also suggested the possibility of the reduction of plastic intermittency [119][120][121]. The framework proposed in Section 2.4, and particularly our equations (4) and ( 5), can be used to rationalize these observations.…”

Crackling noise and avalanches in minerals

“…The mild movements still constitute avalanches in the description of (Salje and Dahmen 2014). Coexistence of mild and wild movements is well known for restructuring processes in many materials under external forcing, like ice (Weiss 2019), martensites (Chen et al 2019), dislocation (Pan et al 2019) and in crack propagation (Bonamy et al 2008;Laurson et al 2010). Mild processes are much more difficult to observe than spiky jerks (Casals et al 2019) where the optical observation of domain wall movements proved particularly useful (Casals et al 2020).…”