【作者】 叶林凤；

【导师】 张喜燕；

【作者基本信息】 广西大学 ， 材料物理与化学， 2008， 硕士

【摘要】 锆合金热中子吸收截面小,具有较好的耐腐蚀和高温力学性能,而广泛应用于核动力反应堆中作为燃料包壳材料和堆内结构材料。作为反应堆安全运行的第一道屏障,包壳的内壁受到裂变产物的侵蚀,外壁受到高温高压水的冲刷和腐蚀、中子辐照损伤及腐蚀吸氢都将导致包壳的力学性能下降。因此,提高包壳材料的耐腐蚀性能是首要任务。目前改善包壳的水侧耐蚀性能主要途径有:成分调整、组织控制和表面处理。本文通过对表面纳米组织以及普通粗晶组织Zr-4合金在高压釜中673k/10.3MPa条件下进行腐蚀试验,并对基体以及不同腐蚀时间的氧化膜进行透射电镜、扫描电镜以及X射线衍射观察与分析,主要得出以下结论:1、经高速喷丸处理后的Zr-4合金,通过TEM观察研究可知其平均晶粒尺寸随深度呈梯度变化。所得到的样品按平均晶粒尺寸的大小可分为三层:表层是平均晶粒尺寸为几纳米至十几纳米纳米组织结构比较致密和完整的的纳米层,其次为晶粒尺寸为几百纳米的过渡层,最后是靠近心部的组织仍保留原来粗晶组织结构的基体层。2、高压喷丸技术使Zr-4合金表面自纳米化的晶粒细化机理是:在不断加载的情况下,不同取向的孪晶之间的相互交截作用以及高密度位错的运动是导致晶粒细化并获得纳米晶体的主要原因。3、42天腐蚀试验后的TEM观察表明,普通粗晶Zr-4合金中ω-Zr层处的腐蚀程度比较严重,而纳米组织Zr-4合金中ω-Zr层处的腐蚀情况比较轻微,只有晶界附近被氧化。4、表面纳米化Zr-4合金的腐蚀幂函数n值比普通Zr-4合金的n值小,说明纳米组织Zr-4合金的腐蚀产物更具有保护性,其抗腐蚀性能优于普通Zr-4合金。5、表面纳米组织Zr-4合金的腐蚀速率转变时间为100天,而普通粗晶Zr-4合金的转变时间为42天左右,这表明纳米化Zr-4合金的腐蚀产物更具有保护性。6、利用X射线衍射（XRD）方法计算分析氧化膜内的应力大小得出表面纳米化Zr-4合金氧化膜内存在较大微观应力,而高的压应力有利于t-ZrO₂相的稳定,延缓相变的进行,从而降低腐蚀速率。实验数据表明,纳米组织Zr-4合金的腐蚀性能比粗晶组织Zr-4合金又更加优异的抗腐蚀性能。但是,影响表面纳米化Zr-4合金的腐蚀性能的因素不仅仅包括晶粒尺度,还包括合金成分、热处理工艺方法、表面状态、反应堆水化学、水冷却剂温度、辐照效应等等。而上述因素中的任何一个因素发生变化,都会导致材料腐蚀性能的改变。因此应全方位综合考虑这些因素的影响,从而全面认识锆合金的腐蚀性能与机制。更多还原

【Abstract】 Zirconium alloys are widely used as fuel claddings and internals in water-cooled nuclear reactors, due to its low thermal neutron capture cross-section, reasonable mechanical properties and adequate corrosion resistance in high temperature water. As the first safety barrier in reactors, fuel claddings are attacked by radioactive fission products and high temperature water. Waterside corrosion resistance becomes a key issue to be improved by composition adjustment, structure modification and surface treatment.In this paper, the matrixes and the oxide films of surface nano-structure (SNS)Zircaloy-4 alloy, as well as the coarse-grain structure(CGS) Zircaloy-4 alloy have been analyzed by means of TEM, SEM and XRD. Corrosion experience were operated in autoclave under the condition of 673k/10.3MPa. We draw conclusions as following:1、After high speed shot-peening(HSSP) processing, nano-structure (ns) layer was successfully obtained on the surface of Zircaloy-4.The final structure was characterized by nano-structure grains layer, ultrafine grains structure layer and basal coarse-grains structure. The mean grain sizes of them were several nano-meters, hundreds nano-meters and gradually to several micrometers respectively.2、The grain refinement mechanism during HSSP treatments proposed as follow: the peening loads will generate dislocations and eventually result in plastic deformation by twining in the surface layer of the material. Under repeated peening loads, grain refinement occurs in the random orientation twining grains through necking and closing off of small lengths of twins, as well as the movement of high-density faults . With the increase of peening time, ns layer will be developed and its thickness increases too.3、The TEM show that, after 42 days’ corrosion period, the corrosion only occurred on the grain boundary inω-Zr layer of SNS Zicaloy-4,while the CGS Zicaloy-4 corrosion seriously.4、The corrosion power function n of SNS Zicaloy-4 is much smaller than that of CGS Zicaloy-4, which indicates that the SNS Zicaloy-4 is much more protected.5、The transition time of corrosion rate of SNS Zicaloy-4 is about 100 days, however, the CGS Zicaloy-4 occurs at about 42 days, which mean that corrosion process of the former is lag behind than the latter.6、The XRD analysis shows that the value of stress in the oxide film of SNS Zicaloy-4 is higher than that of CGS Zicaloy-4, which is helpful to maintain the tetragonal zirconia, so to low down the corrosion rate. Experimental evidences indicated that the ns Zircaloy-4 has better corrosion resistant property. Not only the grain refinement can influence the corrosion resistance of Zircaloy-4, but also the alloy composition, heat treatment technique, the surface condition, chemistry of reactor coolant, temperature of reactor coolant , irradiation effects and so on. Ether of them changes, the corrosion property is change. Therefore, in order to have a comprehensive knowledge about the corrosion properties of Zircaloy-4, synthetically consideration of these factors are necessary.更多还原