Pan Yan, Wu Haijun, Wang Xiaofei, Sun Qiaoyan, Xiao Lin, Ding Xiangdong, Sun Jun, Salje Ekhard K H
State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore.
Sci Rep. 2019 Mar 7;9(1):3778. doi: 10.1038/s41598-019-40526-5.
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 with τ ∼ 2 in the defect free or non-rotatable precipitate states. Rotors change the size distribution to P(s) ∼ exp(-s/s). 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.
压缩纳米柱因位错移动而发出噼啪声，这降低了塑性稳定性。噼啪声的特征是应力下降或应变突发，其在很大尺寸范围内呈比例变化，导致幂律统计。在此我们报告，由于一个违反直觉的原因，这种“经典”行为在钛基纳米柱中并不成立：我们在纳米柱内部定制析出物，这些析出物“调节”位错通量。这并非是因为纳米柱变得太小以至于无法维持大的位错移动，因此该效应与尺寸无关。我们的析出物起到“转子”的作用：局部应力引发夹杂物的旋转，这显著降低了应力幅度。应力下降的尺寸分布同时从幂律变为指数分布。转子就像旋转门一样限制通过的位错数量。因此每次崩塌都变弱了。我们给出了钛基纳米柱（直径在300纳米至2微米之间）的实验证据，在无缺陷或不可旋转析出物状态下，噼啪声的幂律分布为P(s) ∼ s ，τ ∼ 2。转子将尺寸分布改变为P(s) ∼ exp(-s/s)。转子是ω相夹杂物，在应力作用下沿滑移面排列，并将位错滑移限制在小距离内且成核速率很高。这为使纳米柱更稳定开辟了新途径。
