The Mechanism of Plastic Deformation in Quasicrystals

本研究的目的是通过分析位错滑动的基本过程来阐明准晶塑性变形的微观机理。对单晶准晶进行高温变形，并对其塑性变形进行热激活分析和电镜观察。Al-(Cu, Ni)- co十方准晶的主要结果是：【环圈1】屈服强度对样品的质量有敏感的依赖性：高质量样品的屈服强度是低质量样品的两倍；【encircled2】滑移在周期方向上的屈服应力与准周期方向上的屈服应力差别不大，【encircled3】引入的位错是直线的。Al-Pd-Mn二十面体准晶的主要结果是：【encircled1】由应力松弛试验估计的相缺陷产生的位错滑动的拖应力在流动应力的20 ~ 50%范围内，【encircled2】真应力与真应变的对比分析表明，在真应变为0.5左右达到最大值后，真应力不断向最小值降低，然后在高应变时逐渐硬化。【encircled3】活化分析表明，最大流动应力和最小流动应力受不同的活化焓控制。基于这些结果，我们提出了以下微观变形机制：【encircled1】对位错滑动的阻力由相应变产生的非热分量和佩尔斯势产生的热分量组成，【encircled2】由于晶格的准周期性，扭结对形成焓不是唯一的；在完美准晶格中，位错滑动速度受较大的扭结对形成焓的支配，而在相缺陷准晶格中，由于扭结迁移比扭结对形成容易得多，位错滑动速度受较小的扭结对形成焓的支配。

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.