析出相对微纳铝单晶强度离散性与位错雪崩的调控规律及微观机理研究

微纳金属单晶的力学行为具有强随机性，表现在两方面：（1）强度高度离散；（2）位错呈雪崩式运动，导致材料在无法预知的瞬间突发尺寸不定的塑性变形。析出相可有效抑制此随机行为，但作用机理还不明确，尚未如析出强韧化一样形成理论体系。尤其是，目前研究从随机位错雪崩整体统计规律出发，还未能表征位错雪崩单体激发和演化的微观进程，及其析出调控；另一方面，本申请明确论证，强度离散规律强烈依赖于位错雪崩的强弱，而这一关联尚未建立。本项目将以铝和铝合金单晶微柱为模型材料，利用新型纳米力学测试系统，研究微纳力学随机行为的尺寸效应和析出调控。本项目致力于，首次精确测量位错雪崩单体的平均速率构型，从而窥探析出相对位错雪崩形成和演化调控的微观机制；探明强度离散性和位错雪崩之间的本质关联；利用先进的晶格位错动力学模拟，系统性地绘制析出调控图谱。研究结果可为金属单晶在微纳尺度下的安全服役提供理论借鉴和模型参考。

Submicron and nano-sized single crystals are featured by stochasticity under external driving, in views of the strongly scattered strength and the random dislocation avalanches prevailing during plastic flow. Consequently, small crystals may collapse plastically under unpredictable external stress. We focus on the ability to control this stochasticity by metallurgical methodologies and have quantified the effects of precipitates on the statistics of dislocation avalanches. However, these studies only analyzed dislocation avalanches statistically, without entering microscopic details of a single avalanche for technical obstacles. As a result, fundamental mechanisms of precipitate effects on the evolution process of dislocation avalanches at small time scales remain unknown. On the other hand, we clearly show in this proposal that the strength statistics and the dislocation avalanches, which were always investigated separately, essentially dependent on each other. By using Al and Al alloys as a model system, we will precisely measure the average velocity shape of dislocation avalanche based on a novel nanomechanical testing system and an advanced dislocation dynamic simulation method, allowing us to investigate coupling effects of precipitates and external size on the evolution process of dislocation avalanches for the first time. We will also study the strength statistics in a same framework with dislocation avalanches, with an aim to systematically understand the stochasticity at small scales and build a comprehensive precipitation tuning map. The results will benefit the security service of single crystals for the obtained theoretical interpretations and quantitative model from this proposal.