【作者】 刘玲；

【导师】 陈鼎；

【作者基本信息】 湖南大学 ， 机械工程， 2022， 硕士

【摘要】 锆合金因其优异的综合机械性能、导热性能、抗辐照能力和耐水侧腐蚀性能被广泛应用于核反应堆的燃料包壳材料和结构材料。目前,国际上应用最广的是Zr-Sn系合金Zr-2和Zr-4。为了应对更高的燃耗要求,各国开始开发新型锆合金,目前比较主流的研究方向是Zr-Sn-Nb系合金,中国也紧跟国际研究前沿趋势,研发了N18、N36等Zr-Sn-Nb系合金。锆合金的吸氢和腐蚀行为对其使用性能和使用寿命影响较大,因此Zr-Sn-Nb系合金的综合吸氢性能、耐腐蚀性能及其吸氢和腐蚀机理是目前的研究热点。尽管研究人员对Zr-Sn-Nb系合金的吸氢或腐蚀性能分别进行了探索,但针对Zr-Sn-Nb系合金吸氢和腐蚀之间关系的关注度较少,并且对于氢加速腐蚀现象的机理有多种解释,目前尚无定论。故本文研究对象为两种新型Zr-Sn-Nb系合金,通过电化学工作站,对材料进行电解渗氢,引入不同程度的氢含量,使其表面具有氢化层。使用金相显微镜（OM）、扫描电镜（SEM）、能谱分析（EDS）、X射线衍射（XRD）等分析手段,对渗氢前后、氧化前后以及电化学腐蚀前后的两种Zr-Sn-Nb系合金进行表征;研究了渗氢时间对材料吸氢量以及吸氢产物的影响;通过氧化实验研究了在氢化锆层上生长的氧化膜组成和形貌;通过电化学分析手段研究了不同氢含量时,两种Zr-Sn-Nb系合金的电化学腐蚀行为,并探讨了电解渗氢时的吸氢机理和腐蚀机理。研究结果表明:（1）Zr-Sn-Nb合金A渗氢时间小于24 h时,氢化物类型为δ-Zr H_1.66,渗氢时间达到24 h及以上时,氢化物类型为δ-Zr H_1.66和ε-Zr H_1.801;Zr-Sn-Nb合金B渗氢后,相组成主要为α-Zr、δ-Zr H_1.66,渗氢时间达到48 h出现ε-Zr H_1.801相。δ-Zr H_1.66相含量随渗氢时间增加而增加,氢化物聚集程度随渗氢时间增加而加重。渗氢后,Zr-Sn-Nb合金A表面氢化锆聚集性比Zr-Sn-Nb合金B大。（2）氧化实验表明:渗氢时间小于24 h时,两种Zr-Sn-Nb合金的氧化膜呈黑色,由T-Zr O₂和M-Zr O₂组成,结构比较致密;当电解渗氢时间达到24 h及以上时,Zr-Sn-Nb合金A中M-Zr O₂含量上升,氧化膜出现分层,结构较为疏松。（3）动电位极化实验表明:两种Zr-Sn-Nb合金渗氢后,腐蚀电位正移,Zr-Sn-Nb合金A的腐蚀电流密度和腐蚀速率随渗氢时间呈波动性变化。Zr-Sn-Nb合金B的腐蚀电流密度和腐蚀速率随渗氢时间增加而增加。渗氢时间小于24h时,Zr-Sn-Nb合金A的耐腐蚀性优于Zr-Sn-Nb合金B。在两种Zr-Sn-Nb合金中都发生了钝化现象。（4）电化学阻抗谱实验表明:不同电解渗氢时间的Zr-Sn-Nb合金A与原材料相比,其电荷转移电阻Rct从大到小依次为A-24h、A-8h、A-0h、A-4h、A-48h,表明氢含量最高的A-48h溶解趋势和溶解速率最大,A-24h耐腐蚀性最好,此时氢含量为270 ppm。阻抗谱测试结果则表明在氢含量较小时,钝化膜致密性上升,氢含量较大时,钝化膜具有较多孔隙,缺少保护性。更多还原

【Abstract】 Zirconium alloys have been used in nuclear reactor as fuel cladding materials and structural materials due to their excellent comprehensive mechanical properties,thermal conductivity,radiation resistance and water-side corrosion resistance.The most widely used cladding materials are Zr-2 and Zr-4.In order to deal with higher fuel consumption requirements,many countries have begun to develop new zirconium alloys.At present,the researchers mainly focused on Zr-Sn-Nb alloys.China has also independently developed new zirconium alloys such as N18 and N36.The hydrogen absorption and corrosion of zirconium alloys have always been the two major factors restricting their long-term application performance.Therefore,the hydrogen absorption performance,corrosion resistance and their mechanism of Zr-Sn-Nb alloys are the current research hotspots.Although researchers have separately explored the hydrogen absorption or corrosion properties of Zr-Sn-Nb alloys,less attention has been paid to the relationship between hydrogen absorption and corrosion of Zr-Sn-Nb alloys.For the phenomenon of hydrogen accelerated corrosion has many discussions and its mechanism remains unclear.In this paper,the cathodic hydrogen charging method is applied to introduce a slice of hydrides on the surface of two kinds of Zr-Sn-Nb alloys.These two kinds of Zr-Sn-Nb alloy before and after hydrogenation,oxidation and corrosion were characterized by optical microscope（OM）,scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）and X-ray diffraction（XRD）.The influence of hydrogenation time on the hydrogen content and hydride distribution was studied;the composition and morphology of the oxide film grown on the bulk hydrid e are studied after oxidation experiments;Corrosion resistance of pre-hydride Zr-Sn-Nb alloys are studied by electrochemical methods.The mechanism on the impact of hydrogen on electrochemical behavior was discussed.The results show that:（1）When the cathodic charging time of Zr-Sn-Nb alloy A is less than 24 h,the hydride phase isδ-Zr H_1.66;when the cathodic charging time up to 24 h,the hydride phases areδ-Zr H_1.66 andε-Zr H_1.801;After hydrogenation,the phase composition of Zr-Sn-Nb alloy B areα-Zr andδ-Zr H_1.66,theε-Zr H_1.801 phase appears when the cathodic charging time reaches 48 h.The content ofδ-Zr H_1.66 phase increases by increasing cathodic charging time.The aggregation of hydride increases with the increase of cathodic charging time.After hydrogenation,the surface of Zr-Sn-Nb alloy A has a greater aggregation of zirconium hydride than that of Zr-Sn-Nb alloy B.（2）Oxidation experiment results show that when the electrolytic hydrogenation time is less than 24 h,the oxide films of the Zr-Sn-Nb alloys A and B are black,composed of T-Zr O₂ and M-Zr O₂ with the dense structure;When the electrolytic hydrogenation time exceeds 24h,the surface of Zr-Sn-Nb alloy A change to white and the content of M-Zr O₂ increased,the oxide film was delaminated with loose structure.（3）Potentiodynamic polarization results show that the corrosion potential of Zr-Sn-Nb alloys A and B moved positively after hydrogen ation.The corrosion current density and corrosion rate of Zr-Sn-Nb alloy A fluctuated with the increase of hydrogenation time.The corrosion current density and corrosion rate of Zr-Sn-Nb alloy B increased with the hydrogenation time.When the hydrogenation time is less than 24 h,the corrosion resistance of Zr-Sn-Nb alloy A is better than that of Zr-Sn-Nb alloy B.Passivation occurs in both Zr-Sn-Nb alloys A and B.（4）Impedance spectroscopy results show that the charge transfer resistance Rct of Zr-Sn-Nb alloy A from large to small is A-24h,A-8h,A-0h,A-4h,A-48h.The results show that A-48h,which has the highest hydrogen content,has the largest dissolution tendency and worst corrosion resistance,while A-24h has the best corrosion resistance.The results indicate that the passive film formed on the bulk hydrides is porous and less of protection.更多还原