【摘要】 用透射电镜、扫描电镜和扫描探针显微镜研究了锆-4样品在高压釜中(360℃/18.6MPa去离子水)腐蚀后氧化膜的断口形貌、氧化膜不同深度处的显微组织和晶体结构。结果表明:氧化膜生成时形成的压应力,使晶体中产生了许多缺陷,稳定了一些亚稳相,在氧化膜底层中有单斜、四方、立方晶体结构甚至非晶相存在;在氧化膜的中间层及表面层中,空位和间隙原子等缺陷发生扩散、湮没和凝聚,内应力发生弛豫,亚稳相转变成稳定的单斜结构;空位被晶界吸收形成了纳米尺寸的孔洞簇,弱化了晶粒间的结合力,在表面张力的作用下,晶粒逐渐成为球形;孔洞簇的形成并发展成裂纹,使氧化膜失去了原有良好的保护性,导致腐蚀转折,这是氧化膜的显微组织在腐蚀过程中发生演化后的必然结果。更多还原

【Abstract】 The microstructure and crystal structure of oxide films in different depth of oxide thickness, and the morphology of fracture surface of oxide films, which are formed on Zircaloy-4 specimens during the autoulave tests in deionized water at 360 ℃/ 18.6MPa, have been investigated by transmission electron mi- croscopy, scanning electron microscopy and scanning probe microscopy. The results show that except the stable monoclinic crystal structure, the meta-stable phases including cubic, tetragonal and amorphous phases can be observed in the bottom layer of oxide films due to the presence of defects induced by the compressive stress in oxide crystals during the formation of zirconium oxide. Under the action of temperature, stress and time, the diffusion, annihilation and condensation of defects as vacancies and interstitials will be taken place in the middle and surface layer of oxide films. The inner stress of oxide crystals will be relaxed and the meta-stable phases will transform to the stable phase. Vacancies absorbed by grain boundaries form the clus- ters of pores in nanoscale, which will weaken the bonding force between grains. In this case, the grains will become gradually spherical due to the action of surface tension. Based on the formation of the clusters of pores and the development of cracks in oxide films,the phenomenon of corrosion transition will be induced due to the loss of protective characteristic of oxide films. This is an inevitable result caused by the micro- structure evolution of oxide films during the autoulave tests.更多还原