【作者】 刘瑶；

【导师】 王正品；

【作者基本信息】 西安工业大学 ， 材料加工工程， 2012， 硕士

【摘要】 M5锆合金以其优越力学性能和耐腐蚀性能在核电站包壳管材料中得到了广泛应用。然而随着反应堆技术向高燃耗、长换料周期方向的发展,对现有的包壳材料提出了更高的要求。本研究针对在M5锆合金焊接封头中含有板条马氏体组织以及马氏体组织在钢铁材料中的优异表现,开展对M5锆合金马氏体化的相关研究工作,以期通过改变M5锆合金的组织结构而达到提高其力学性能和耐腐蚀性能的目的,进而满足核反应堆技术的发展需要。本文采用金相显微镜、透射电镜、维氏硬度试验、动态腐蚀试验和能谱分析等测试手段分别对M5锆合金焊接封头的组织结构和力学性能、Zr-4合金和M5锆合金的腐蚀动力学和耐腐蚀性能以及腐蚀产物及形貌进行了比较系统的研究,主要研究结果如下：M5锆合金包壳管焊接封头金相和透射观察表明：在室温下M5锆合金母材的显微组织为αzr+βNb,,β相较均匀地分布于α相内；焊缝中心部位组织主要为晶界a-Zr (Nb)+棒针状马氏体,透射电镜下可见清晰而规则的板条α’马氏体束及板条束内大量位错分布；热影响区基本为a-Zr (Nb)和板条α’马氏体两相共存或a-Zr、βNb及板条α’马氏体三相共存的组织状态。α’马氏体板条束的宽度由焊缝中心至过渡区逐渐变小。由同心圆截点法对M5锆合金包壳管焊接封头的晶粒度研究结果显示,焊缝中心区域的晶粒度高达六级到七级,熔合线附近的晶粒度为八级到九级,热影响的晶粒度达到九级到十级,而母材晶粒相当细小,晶粒度仅为十三级到十四级。M5锆合金包壳管焊接封头显微硬度试验结果表明,M5锆合金焊接封头焊缝中心硬度值高于热影响区和母材,由焊缝—热影响区—母材顺序依次呈抛物线降低。纵向显微硬度因为电子束的堆焊,使得峰值出现在热影响区。这和焊缝中心板条α’相马氏体及期内的大量位错分布密切相关。对Zr-4合金和M5锆合金的380℃和400℃动态腐蚀试验结果表明,两种合金在不同温度下的腐蚀动力学曲线均符合抛物线规律,但M5锆合金的腐蚀速率要明显低于Zr-4合金。扫描电镜形貌观察显示,腐蚀后两种合金的表面颜色变成黯灰色,但仍具有金属光泽。其中Zr-4试样表面出现灰白色块状氧化膜,出现了轻微的疖状腐蚀,而M5表面则未发现疖状腐蚀。同时,Zr-4腐蚀层与包壳管基体金属的结合不如M5牢固。能谱分析则表明,两种合金的腐蚀产物均为Zr02和ZrO的固溶物。更多还原

【Abstract】 As the cladding material of light-water nuclear reactor, M5 zirconium alloy is widely used in industrial applications with its excellent mechanical properties and corrosion resistance,. However, with the development of the nuclear reactor technology of high fuel consumption and long period of changing the cladding material, there is a new challenge for the exsiting cladding material. In view of the good performance of the martensite in steel, The comprehensively study on the martensite in M5 alloy welding joints to meet the needs of the development of the nucear power plant.The microstrucuture, mechanical properties, corrosion dynamics, corrosion resistance and corrosion products of Zr-4 and M5 alloy were mainly investigated by using of OM, TEM, SEM, Vickers hardness test, dynamic corrosion test and energy spectrum analysis. The results were as follows.The metallograph and microhardness test of M5 alloy cladding tube showed that the structure of base metal was azr+βNb with fineβNb homogeneously distributed in azr matrix. The soldered area consists of grain boundary a-Zr (Nb) and acicular martensite with high density of dislocations under TEM; The microstructure of HAZ presents the coexisting structures of a and a’duplex phases system, or the three-phase coexisting strucuture of a’,α’andβ. The width of martensite became narrower from WM to HAZ. The Grain size of Center of the weld was 6-7, the fusion zone is 8-9 and the size of base metal was only 13-14.Microhardness test indicated that the grain size of melted zone on the welding plug head was higher than that of other positions. For the different distributions of dislocations the highest microhardness value was on HAZ.The dynamic corrosion test at 380℃and 400℃revealed that the corrosion dynamics of Zr-4 and M5 alloys abided by parabolic law and the corrosion speed of M5 alloys was obviously lower than that of Zr-4 alloys. The surface of the two alloys changed from bright to gray. There were some tiny gray oxidation film on the surface of Zr-4 rather than on M5 alloys, which showed that corrosion resistance of M5 was superior to that of Zr-4. The spectrum analysis showed the oxide products of M5 were probably ZrO2 and ZrO.更多还原