The Mechanism of Plastic Deformation in Quasicrystals

本文旨在通过对位错滑移基本过程的分析，阐明准晶塑性变形的微观机制。我们在高温下使单个准晶变形，并进行了塑性变形的热激活分析和电子显微镜观察。对Al-（Cu，Ni）-Co十次准晶的主要结果是：屈服强度对样品质量敏感，高质量样品的屈服强度是低质量样品的两倍，周期方向和准周期方向的屈服应力相差不大，引入的位错是直的。Al-Pd-Mn二十面体准晶的主要结果是：由于相位子缺陷产生而引起的位错滑移的拖曳应力（其已经从应力松弛测试中估计）在流动应力的20 - 50%的范围内，真应力vs真应力-应变分析表明，在出现最大值后，真应力在真应变为0.5左右时继续向最小值下降，然后变为逐渐硬化在较高应变下，[encircled 3]激活分析表明，最大流变应力和最小流变应力由不同的激活模式控制。基于这些结果，我们提出以下微观变形机制：位错滑移的滑移阻力由相子应变产生的非热分量和Peierls势产生的热分量组成，由于晶格的准周期性，扭结对形成焓不是唯一的，在理想准晶格中，位错滑移速度由大的扭结对形成焓决定，而在相位缺陷准晶格中，位错滑移速度由小的扭结决定。对形成焓，因为扭结迁移比扭结对形成容易得多。

The purpose of the present research is to ellucidate the microscopic mechanism of plastic deformation of quasicrystals by analyzing the elementary process of dislocatin glide. We deformed single quasicrystals at high temperatures, and performed thermal-activation analysis of plastic deformation and electron microscopy observation. The main results for Al-(Cu, Ni)-Co decagonal quasicrystals are : 【encircled1】the yield strength depends sensitively on the quality of the sample : those of high quality samples are twice as high as those of low quality samples ; 【encircled2】the yield stress for slip in periodic direction is not much different from that in quasiperiodic direction, 【encircled3】dislocations introduced are straight. The main results for Al-Pd-Mn icosahedral quasicrystals are : 【encircled1】the dragging stresses for the dislocation glide due to phason defect production, which have been estimated from the stress-relaxation tests, are in the range of 20 to 50% of the flow stress, 【encircled2】true-stress vs true-strain analysis shows that after exhibiting maximum the true stress continuously decreases towards minimum at around the true strain of 0.5 and then changes to gradual hardening at higher strain, 【encircled3】activation analysis showed that the maximum flow stress and minimum flow stress are governed by different activation enthalpies. Based on these results, we propose the following microscopic deformation mechanism : 【encircled1】glide resistance to dislocation glide consists of athermal component due to phason strain production and thermal component due to Peierls potential, 【encircled2】due to the quasiperiodicity of the lattice the kink-pair formation enthalpy is not unique, 【encircled3】in the perfect quasilattice the dislocation glide velocity is governed by the large kink-pair formation enthalpy while in phason-defected quasilattice it is governed by small kink-pair formation enthalpy since kink migration is much easier than the kink-pair formation.