690TT合金在高温含铅碱液中的腐蚀行为

室温条件下690TT合金的极化曲线表明,加入氧化铅能导致合金表面钝化膜不稳定。静态高压釜高温含铅碱液中的浸泡实验表明,在330℃的10% NaOH+10 g/L PbO含铅碱液中,690TT合金发生晶间腐蚀,试样失重,且试样表面越粗糙,腐蚀越严重。其中线切割样品由于残余应力和腐蚀产物楔入应力的综合作用,晶间腐蚀发展成为沿晶应力腐蚀开裂。在330℃的10% NaOH碱液中,690TT合金没有发生晶间腐蚀。     

蒸气发生器用690TT合金的组织结构和腐蚀性能

蒸汽发生器(SG)管子破坏的最主要原因是一次侧应力腐蚀裂纹SCC(ID),二次侧应力腐蚀裂纹SCC(OD)或晶间腐蚀(IGA)也是管子破坏的重要原因,总的说来,腐蚀问题是导致80%以上管子破损的原因。对690TT合金的应力腐蚀和晶间腐蚀进行了试验,另外对其组织及断口等也进行了分析。     

划伤690TT合金在高温含氧水中应力腐蚀裂纹萌生的研究

利用划伤技术研究了690TT合金在325 ℃高温含氧硼锂水中的裂纹萌生和生长情况。试样表面和截面显微分析的结果表明,划伤沟槽底部局部萌生了典型的沿晶应力腐蚀裂纹。由于应力集中,在慢速率拉伸阶段划伤沟槽底部产生了机械裂纹,而机械裂纹成为恒载过程中690TT合金沿晶应力腐蚀裂纹萌生和生长的先导。尖端非常接近晶界或者沿着晶界的机械裂纹可继续形成沿晶应力腐蚀裂纹。690TT合金在恒载荷条件下对应力腐蚀开裂仍有一定的敏感性。     

丁磨态690TT合金经不同时间浸泡后表面氧化膜结构分析

利用多种分析手段深入分析了打磨处理的690TT合金在模拟压水堆—回路高温高压水环境中经不同时间浸泡后表面生长的氧化膜的微观结构.结果表明,从短期氧化到长期氧化,氧化膜表面形貌变化不明显;氧化膜主要由尖晶石结构的氧化物和单质Ni构成.浸泡96和1440 h后,氧化膜主要由富含Cr的氧化物构成.浸泡720,1440和216...     

打磨态690TT合金经不同时间浸泡后表面氧化膜结构分析

利用多种分析手段深入分析了打磨处理的690TT合金在模拟压水堆一回路高温高压水环境中经不同时间浸泡后表面生长的氧化膜的微观结构.结果表明,从短期氧化到长期氧化.氧化膜表面形貌变化不明显;氧化膜主要由尖晶石结构的氧化物和单质Ni构成.浸泡96和1440 h后,氧化膜主要由富含Cr的氧化物构成.浸泡720,1440和2160 h后,氧化膜均由外层、中间层和内层构成:外层是分散的富含Ni和Fe的尖晶石结构的大颗粒氧化物;中间层是致密的富含Cr的尖晶石结构的小颗粒氧化物;内层是均匀连续的富含Cr的氧化物.中间层和内层氧化物能对基体起到良好的保护作用;随着氧化时间的延长,保护层的平均生长速率逐渐降低.打磨处理促进了690TT合金表面保护性氧化膜的生长.     

电解抛光态690TT合金经不同时间浸泡后表面氧化膜结构分析

利用AFM,SEM,TEM,EDS及XPS分析了电解抛光处理690TT合金在含B和Li,充H_2的高温高压水溶液中经不同时间浸泡后表面生长氧化膜的微观结构.结界表明,从短期氧化到长期氧化,氧化膜表面形貌变化不明显;氧化膜主要由具有尖晶石结构的氧化物和单质Ni构成.浸泡720,1440和2160h后,氧化膜均由外层、中间层和内层构成:外层是分散的富含Ni和Fe的尖晶石结构的大颗粒氧化物;中间层是疏松的富含Ni的尖晶石结构的针状氧化物;内层是连续致密的富Cr氧化物.仅氧化膜中的内层氧化物能对基体起到良好的保护作用.电解抛光处理不利于690TT合金表面保护性氧化膜的快速生长.浸泡至2160 h后,氧化膜依然缺乏保护性.内层氧化膜的平均生长速率并未显著降低.     

TT处理对690合金微观组织结构的影响

采用扫描电子显微镜(SEM)、背散射电子衍射分析技术(EBSD)研究了TT处理对690合金微观组织结构的影响。研究表明:TT处理不仅可以控制晶界碳化物的析出,还可以影响织构的方向和程度。690合金在715℃TT处理10h能够获得致密连续的晶界碳化物。TT处理前690合金在2个方向上存在密排,而在TT处理后密排只存在1个{111}方向。TT处理对低ΣCSL(coincidence site lattice)晶界的比例基本没有影响。TT处理对织构方向的影响可能会在690合金的抗应力腐蚀性能表现出来。     

表面状态对690TT合金腐蚀及应力腐蚀行为的影响

采用扫描电镜、原子力显微镜和表而粗糙度测量仪对具有不同表面状态的690TT合金表面形貌进行了表征与比较。采用零电荷电位测量、动电位扫描和电化学快慢扫描等方法对不同的690TT合金的腐蚀行为进行了比较。结果表明,与机械抛光样品相比较,打磨样品表面起伏较严重,拥有更大的表面粗糙度值;在相同的腐蚀环境中,打磨样品比机械抛光样品表现出更大的腐蚀速度和更高的应力腐蚀开裂敏感性。分析认为,单纯的表面较大粗糙度和残余应变均能够促进690TT合金的腐蚀。实验中打磨690TT样品表现出的较高腐蚀速度和应力腐蚀开裂敏感性是由其较大的表面粗糙度和表面残余应变综合影响结果。     

690TT合金在特殊环境下的腐蚀问题

在广泛的电厂运行及实验室研究基础上,690TT合金被证明是目前最佳的蒸汽发生器（SGs）管材之一,690TT合金的使用有效地提高了PWR蒸汽发生器的可靠性,因而成为在役第二代核电站中最常用的传热管管材,并将大量应用于第三代商用核电厂。然而在水质恶化以及随服役时间的增加,690TT合金不可避免的也会遭遇腐蚀。本文对690TT合金使用安全性造成潜在威胁的脱合金成分腐蚀（Cr贫化）、铅致应力腐蚀破裂（PbSCC）、低价硫应力腐蚀开裂（Sy-SCC）的情况加以较详细的介绍。     

蒸汽发生器管690TT合金的点蚀性能

通过化学浸泡试验、动电位极化曲线的测量并结合扫描电镜(SEM)对经特殊热处理的690合金(690TT)点蚀形貌的观察,研究探讨了两种国产690TT合金在室温下的点蚀性能;并根据ASTM G48A与ASTM G61两种标准对690TT合金抗点蚀性能评估进行了比较。结果表明:两种国产690TT合金中,合金B的抗点蚀性能显著优于合金A的。ASTM G48A对690TT合金进行点蚀试验的最佳试验参数为50℃/3h,所得相应数据结果可靠;由于缝隙腐蚀等原因使ASTM G61对690TT合金管的点蚀电位测量稳定性不佳,可重复性较差。     

Intergranular attack and intergranular stress corrosion cracking of Alloy 690 TT in high temperature lead‐containing caustic solution

Immersion tests were carried out in high temperature lead‐containing caustic solution in a static autoclave. The results showed samples with three surface statuses of Alloy 690 TT suffered from intergranular attack (IGA) after immersion in 10% sodium hydroxide (wt%) with 10 g/L of litharge at 330 °C for different times. With the increasing immersion time, IGA became more severe. Wire cutting samples had the most serious IGA, ground samples followed and electro‐polished samples had the slightest IGA. IGA had developed into IGSCC only in wire cutting samples due to the existence of residual stress. All the specimens at different immersion time tests lost weight. To the same cold‐work samples, with the increasing immersion time, the weight loss increased. No IGA was found in 10% sodium hydroxide solution at 330 °C after 720 h immersion. When adding 100 ppm litharge into 10% sodium hydroxide solution, slight IGA was produced. IGA became more serious and the weight loss of the specimens with three surface statuses increased with the increase of lead concentration. As the results of 1% sodium hydroxide solution containing 10 g/L litharge and 4% sodium hydroxide solution containing 10 g/L litharge at 330 °C for 720 h immersion tests, only slight IGA occurred and the weight of samples with three surface statuses increased. The pH value played an important role in lead‐induced corrosion in caustic solution.     

Cl~-对690合金在高温高压水中腐蚀行为的影响

采用扫描电子显微镜和X射线衍射仪研究了Cl-对690合金在高温高压水中腐蚀行为的影响。研究表明:690合金内外表面状态对其腐蚀形貌有显著影响,Cl-使得表面形成的钝化膜不均匀,出现较多的点蚀坑。溶液中的Cl-能够影响腐蚀产物膜的结构。当溶液中不含有Cl-时,腐蚀产物膜为双层结构,外层腐蚀产物为颗粒状;当溶液中含有Cl-时,腐蚀产物膜具有单层结构。XRD结果表明:两种环境中的钝化膜产物主要由Cr2O3、NiFe2O4、NiO等氧化物组成,但含Cl-条件下的氧化物较少。     

Influence of Zn on oxide films on Alloy 690 in borated and lithiated high temperature water

To clarify the corrosion control effect of Zn injection into hydrothermal environments, the oxide films on Alloy 690 in the deaerated borated and lithiated water have been investigated using potentiodynamic polarization curves, electrochemical impedance spectra at 300 °C and ex-situ X-ray photoelectron spectroscopy. With Zn injection in the solution, ZnCr₂O₄ and ZnFe₂O₄ were formed in the inner and outer layers of the oxide films on Alloy 690, respectively, through exchange reactions between Zn²⁺ and Fe²⁺/Ni²⁺. A simple model for oxide film structure change and the mechanism of corrosion inhibition by Zn injection is proposed and discussed.     

Influence of pH on electrochemical properties of passive films formed on Alloy 690 in high temperature aqueous environments

Passive films formed on Alloy 690 in different pH solutions at high temperatures were studied by potentiodynamic polarization, Auger electron spectroscopy, thermodynamic diagrams and the Mott–Schottky relation. The chemical compositions and electronic structures of the passive films were found to be strongly pH-dependent. In alkaline solutions, a secondary passivation was clearly observed on potentiodynamic polarization curves. The passive films were a mixture of Cr₂O₃ and FeCr₂O₄ below the flat band potential of nickel oxide and were NiFe₂O₄ above this potential. Electronic structure models, describing the electrochemical properties of the passive films, are proposed and discussed.     

Corrosion resistance of SG tubing material Incoloy 800 mod. and Inconel 690 TT

The corrosion resistance of the SG tubing material Incoloy 800 mod. and Inconel 690 TT is considered with respect to pitting, sensitization characteristics and stress corrosion cracking, especially chloride-induced cracking, pure water cracking and caustic cracking. Based on laboratory data Incoloy 800 mod. as well as Inconel 690 TT show very good corrosion resistance under specified and faulted SG water conditions. The published results often refer to Incoloy 800 according to ASTM B 163–66. It is shown that the Incoloy 800 grade used by nuclear power suppliers is optimized for this application. The restricted chemical composition of the modified grade of Incoloy 800 vs. the standard grade is discussed and it is shown that this results in a significantly higher resistance to the above mentioned corrosion phenomena. The operating experience with Incoloy 800 mod. heat transfer tubes in nuclear steam generators is discussed briefly with respect to corrosion. No materrial-specific weaknesses have been observed with Incoloy 800 mod. Since more than 19 years of operation only at one tube out of 235 000 SG tubes made of Incoloy 800 mod. a leakage caused by corrosion has been occurred. This finding is independent of different tube manufacturers and different water treatments of the various plants.     

Effect of temperature on corrosion and semiconducting properties of oxide films formed on M5 zirconium alloy

Nuclear fuel cladding for pressurised water reactors is commonly manufactured with zirconium alloys. The M5 alloy is a relatively new cladding material for in-reactor used with enhanced performance compared to traditional zircaloys. In this work, the influence of temperature on the corrosion resistance and semiconducting properties of the passive film formed on the M5 alloy in a borate buffer solution has been evaluated. The electrochemical behaviour of the zirconium alloy was assessed by potentiodynamic polarisation tests, electrochemical impedance spectroscopy and Mott–Schottky plots. The results indicated that the corrosion resistance of the M5 alloy decreased with temperature due to the formation of a less stable and more defective passive film. The Mott–Schottky approach used in combination with polarisation tests and impedance measurements was effective to reveal the protective state of the passive film on the M5 alloy.     

Influence of dissolved oxygen on oxide films of Alloy 690TT with different surface status in simulated primary water

Oxidation of Alloy 690 with different surface conditions were performed in oxygenated primary water containing B and Li at 325 °C and 15.6 MPa for 2 months. Oxide scales were analyzed using various methods. Results showed triple-layer oxide films were formed: the outmost layer with dispersed big oxide particles; the intermediated layer with loose sheet-like or needle-like oxides and the inner layer with incompact cellular oxides, which were lack of protectiveness. Oxide morphologies were affected by the surface status of samples. Dissolved oxygen increased the intergranular attack (IGA) sensitivity of Alloy 690TT. Growth mechanism of the oxide film was discussed.     

基于计算机模拟的打磨态690TT合金腐蚀性研究

研究了打磨态690TT合金在动态高温高压水循环腐蚀系统中的腐蚀性能,并采用计算机模拟技术绘制了基体平均腐蚀速率随浸泡时间的变化曲线。结果表明,合金在浸泡55 h以上,表面会形成致密小颗粒和分散大颗粒氧化物保护膜,降低了基体的平均腐蚀速率。     

ME20镁合金阳极氧化膜耐蚀性研究

采用正交试验,开发出一种新型环保镁合金阳极氧化的电解液配方,研究在此工艺下形成的阳极氧化膜的对蚀性.采用EDAX、XRD、SEM对阳极氧化膜的成分、结构和形貌进行研究.结果表明,获得的陶瓷层分布均匀,表面光滑致密,耐蚀性显著加强.     

阳极氧化工艺对6061铝合金草酸氧化膜耐磨耐蚀性的影响

为改善6061铝合金的表面耐磨性能和耐蚀性能,利用阳极氧化技术在草酸电解液中制备了阳极氧化膜。采用显微硬度仪测试了膜层的显微硬度,利用摩擦磨损试验机(CSEM)研究阳极氧化膜的摩擦性能,利用电化学阻抗谱(EIS)分析氧化膜的抗腐蚀性能。研究了阳极氧化电流密度、电解液温度以及阳极氧化时间对氧化膜的硬度、耐磨性及耐蚀性的影响规律,给出综合性能较好的阳极氧化工艺参数:电解液为40 g·L-1的草酸,阳极氧化温度为10℃,阳极氧化电流密度为1.0 A·dm-2,阳极氧化时间为120 min。