Experimental and theoretical approach for mobile defect clusters introduced under heavy ion irradiations

离子和/或中子的辐照使引入晶格缺陷的材料的性能恶化。典型的缺陷之一是位移级联，在置换级联中产生“自发熔化”的体积，留下点缺陷。最近对位移级联的研究表明，间隙原子束是在级联过程中形成的，并且可能以较低的激活能在基质中移动。据推测，缺陷聚集在晶界、析出物、位错等缺陷处，导致装饰和扩散或阻碍位错运动。本工作研究了离子束对微结构演化的影响。本工作包括(1)在与离子加速器连接的透射电子显微镜上进行原位观察和(2)在离子辐照材料中进行横截面观察。(1)制备了完全退火的铜和金的电子透明度，并在670-870K的离子辐照下，在电子显微镜中观察到了与位移级联有关的移动缺陷。典型的行进距离范围为20~140 nm，但由于受观测区域的限制，行进距离上限较大。系统地分析了共格沉淀的寿命和迁移率方向，得出了形成Crowdion型间隙束的结论。(2)在离子辐照作用下，观察到了稀铜-钴体系中共格沉淀应变对比度的相干到非相干转变。这一效应在离子的范围内传播，强烈地表明了克隆子束的扩散，这是由通量、通量和温度的关系得出的结论。上述结果被总结为2007财年的两篇研究论文和一次国际会议。

Irradiation with ions and/or neutrons deteriorates properties of materials introducing lattice defects. One of the typical defects is displacement cascades in which "spontaneously melted" volumes are generated leaving point defects. The recent study on the displacement cascades revealed that bundles of interstitial atoms (crowdion bundles) are formed in the cascade process and may travel in the matrix with low activation energy. The defects are presumed to accumulate at defects such as grain boundary, precipitates, dislocations etc, inducing decorations and diffusion or retarding dislocation motion. In this work, the effects of the crowdion bundles on the microstructure evolution are investigated.This work consists of (1) in-situ observations in a transmission electron microscope (TEM) interfaced with an ion accelerator and (2) cross section TEM in ion-irradiated materials.(1) Electron transparency of fully-annealed copper and gold were prepared and set in the TEM for ion irradiations with heavy ions at the temperature from 670 to 870 K. Mobile defects associated with displacement cascades were observed. The typical traveling distance ranges 20 to 140 nm, however the upper limit was due to the limitation of observation area. The lifetime and the direction of mobility were systematically analyzed, and the formation of crowdion-type interstitial bundle was concluded.(2) Coherent-to-incoherent transition of strain contrast of coherent precipitates in dilute Cu-Co system was observed upon ion irradiation. The effect propagated over the range of ions, strongly indicating diffusion of crowdion bundles which is concluded by fluence, flux and temperature dependences.The above results were summarized as two research papers and an international conference in the fiscal year of 2007.