Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： Three high- entropy alloys Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi were prepared by arc melting. Their phase structure, microstructure and chemical composition were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). A commercial alloy 690TT was used as the contrast material. The repassivation kinetics of the three high entropy alloys in high temperature pressurized water was investigated by means of electrochemical test. The results show that Co1.5CrFeNi1.5Ti0.5Mo0.1, AlCoCrFeNiSi0.1 and TaNbHfZrTi high entropy alloys are all composed of single phase. The crystallographic structure of Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy is fcc, while that of the alloys AlCoCrFeNiSi0.1 and TaNbHfZrTi is bcc. The SEM results show that the Co1.5CrFeNi1.5Ti0.5Mo0.1 alloy showed a typical dendritic microstructure, of which the dendrite riches in Cr and Fe, but the interdendrite zone riches in Ti and Ni. There is no obvious element segregation observed in the AlCoCrFeNiSi0.1 alloy. The TaNbHfZrTi alloy also exhibited a dendritic microstucture, of which the dendrite riches in Ta and Nb, and the interdendrite zone riches in Hf, Zr and Ti. The repassivation rates of these four alloys in high-temperature pressurized water may be ranked as the following sequence: TaNbHfZrTi＞Co1.5CrFeNi1.5Ti0.5Mo0.1＞690TT＞AlCoCrFeNiSi0.1.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Forged 316LNSS has been selected as the main pipe line material used in the third generation nuclear power plants. The oxide scale formed on the forged 316LNSS after immersion in high temperature pressurized water with 2.3 mg/L of dissolved hydrogen (DH) was studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Results showed that a double-layer oxide scale was grown on 316LNSS. The outer Ferich layer was composed of Fe3O4 and hydroxides (mainly Ni(OH)2 and CrOOH) and the inner layer was composed of Cr-enriched spinel oxides. The mechanism of oxide scale formation was also discussed.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The dissimilar metal weld joint (DMWJ) in primary water system of pressurized water reactors (PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus, maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants (NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro-hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone (HAZ) of 316L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution (GBCD) in both the 316L/52Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum-rich precipitates particles distributed both along the grain boundaries and inside grains in the 316L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking (SCC) sensitivity of the precipitates needs to be carried out.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The electropolished (EP) alloy 690TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni. The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized NiO. The stable phase region in the potential-pH diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr-rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The reactor coolant piping in the third generation nuclear power plants of AP1000 is manufactured by integrally forging. Therefore, it is of vital importance to investigate the effects of forging and heat treatments on the stress corrosion cracking (SCC) resistance of 316LN stainless steel (316LNSS), which is the candidate material for the reactor coolant piping in AP1000 nuclear power plants. In this work, electron back scattering diffraction (EBSD) and microhardness measurements (HV) were used to characterize the microstructure and residual strain of the as-received 316LNSS, the forged and solution anneal treated 316LNSS and the forged and stress relief treated 316LNSS, respectively. The average grain size of the as- received 316LNSS was the largest, and the forged 316LNSS followed by solution anneal treatment and stress relief treatment showed no obvious differences on grain size. The as-received 316LNSS exhibited the highest residual strain followed by the forged and stress relief treated 316LNSS and then solution anneal treated 316LNSS. Besides, the residual strain in the as- received 316LNSS concentrated on grain boundaries, while the residual strain in the forged and stress relief treated 316LNSS was characterized by a band-like distribution. The U-bend specimens were utilized to investigate the SCC behavior of the 3 kinds of 316LNSS specimens in high temperature caustic solution. After SCC experiments, the crack morphologies of the 3 kinds of 316LNSS specimens were examined by SEM. Then the macro and micro fracture morphologies were examined by OM and SEM, respectively. Grain morphology, residual strain and grain boundary character distribution near the SCC crack tip of the forged and stress relief treated 316LNSS were investigated using EBSD. The results showed that the forged and solution anneal treated 316LNSS exhibited the lowest SCC sensibility, while the as-received the highest, with the most cracks and the highest growth rate. The as-received and the forged and solution anneal treated 316LNSS showed obvious intergranular cracking, while the forged and stress relief treated 316LNSS showed a mixed cracking mode. The larger average grain size and higher residual strain, especially concentrating on the grain boundaries, were considered to be responsible for the highest SCC sensibility of the as-received 316LNSS. Compared with the forged and stress relief treated 316LNSS, the higher content of coincidence site lattice boundary (CSLB) and lower residual strain contributed to the lower SCC sensibility of forged and solution anneal treated 316LNSS. The stress relief treatment failed to eliminate the band-like microstructure effectively, which disadvantaged the SCC resistance.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of forging on the average grain size, residue strain and grain orientation distribution of nuclear grade 316LN stainless steel (316LNss) was studied by means of electron back scattering diffraction (EBSD). The morphology and chemical composition of the oxide films formed on the as-received 316LNss as well as the forged and solution annealed 316LNss after immersion in borated and lithiated high temperature pressurized water at 300 oC for 190 h were also investigated. The results show that the average grain size was reduced and the residual strain was eliminated by forging and followed solution annealing. There were no obvious textures in the forged and solution annealed 316LNss. A two-layered oxide film grew on 316LNss after immersion in high temperature pressurized water. The outer layer composes of hydroxides and Fe-enriched spinal oxides and the inner layer composes of Cr-enriched spinal oxides. The forged and solution annealed 316LNss exhibited a lower oxidation rate rather than the as received ones due to the formation of a thinner and more Cr-enriched oxide film. The oxidation mechanism was also discussed.
Subjects: Materials Science >> Materials Science (General) submitted time 2017-11-21 Cooperative journals: 《金属学报》
Abstract：高温高压水中的硫对蒸汽发生器合金的腐蚀是最复杂的腐蚀过程之一。本文从热力学计算和实验方面综述了高温高压水中硫致690和800合金腐蚀的研究进展。热力学计算主要以E-pH图、伏特等效图以及离子分布系数曲线呈现，计算结果表明S的价态以及与金属的相互作用主要受温度、pH以及电位的影响，但热力学计算没有考虑S中间产物的影响作用。腐蚀电化学及表面分析结果表明硫致腐蚀受温度、pH值、S离子种类、Cl－等其他杂质离子、晶粒取向、合金成分以及应力等多因素影响，多因素之间可能存在复杂的交互作用。合金中Cr、Mo和Cu的加入可在一定程度上抑制硫致腐蚀，而Ni含量的增加则使硫致腐蚀敏感性增加。S更易吸附在材料表面缺陷处引起局部优先溶解，晶粒取向按照(111)<(100)<(110)硫致腐蚀敏感性增大。
Subjects: Materials Science >> Materials Science (General) submitted time 2017-03-31 Cooperative journals: 《金属学报》
Abstract：采用数值模拟方法对核电站316L不锈钢弯头的应力腐蚀裂纹扩展行为进行了研究。首先针对不锈钢厚壁弯头(外径355.6 mm，内径275.6mm)进行有限元建模,在弯头内壁上创建出与实际裂纹相符的半椭圆状3D缺陷作为裂纹形状,其裂纹张开位移 (δi) 由Dugdale模型计算确定;然后根据有限元计算结果,建立裂纹应力强度因子 (K) 随裂纹深度 (d) 及附加应力 (P) 变化的拟合公式,结合实验数据得到管材在两种冷变形量下的应力腐蚀裂纹扩展速率 (da/dt) 拟合公式,利用迭代方法计算了裂纹穿透管壁所需的时间，为核电站安全评估提供了有效依据.研究显示，当弯头部位的冷变形量较小（硬度为230~245 HV）且在理想情况下 (无初始附加应力) 弯头被应力腐蚀裂纹穿透耗时最长 (约57 a)，当初始附加应力增加至200 MPa此失效时间约缩减至前者的1/5 (无应力释放)、2/7 (应力释放一半) 以及3/7 (应力完全释放)；保持初始附加应力不变(200 MPa)并提高弯头部位冷加工变形量(由硬度为230~245 HV提高到275~300 HV)，弯头的大变形部位被穿透时间约缩短至小变形部位失效时间的2/5（无应力释放）、3/8 (应力释放一半)以及1/3 (应力完全释放)，由此可见应力释放程度的降低和冷加工变形量的增加均导致了核电站316L不锈钢弯头剩余寿命的缩短。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：利用光学显微镜、扫描电子显微镜（配有能谱仪及背散射电子衍射附件）、显微硬度仪、微小试样拉伸试验及慢应变速率拉伸实验对国产带热丝隔离层核电安全端焊接件不同部位的微观结构及局部的力学性能和应力腐蚀敏感性进行了分析研究。发现，在SA508-52Mb界面处的52Mb中具有大量的对应力腐蚀敏感的I型晶界及II型晶界，导致此界面具有最高的应力腐蚀敏感性；SA508热影响区存在明显的组织过渡；316LN热影响区中随着距熔合线距离的增加，CSL的数量分数逐渐增大，Σ3晶界与理想的Σ3晶界的偏差角减小，残余应变逐渐减小，残余应变的最高值出现在对接焊底焊位置处的316LN热影响区中，导致316LN的热影响区也具有较高的应力腐蚀敏感性。焊接件不同部位的性能存在较大的差异，主要是由不同部位的微观结构差异引起的。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-14 Cooperative journals: 《中国腐蚀与防护学报》
Abstract：本文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. 试样的表面和截面显微分析结果表明，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. 尖端接近晶界或者沿着晶界的机械裂纹可继续出现沿晶应力腐蚀裂纹. 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.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用金相显微镜、透射电镜(TEM)、扫描电镜(SEM)、显微硬度仪、原子力显微镜(AFM)、磁力显微镜(MFM)、扫描开尔文探针(SKPFM)等微观分析手段，分析了先进压水堆核电站反应堆压力容器安全端异种金属焊接接头A508/52M/316L的金相组织、显微硬度、主要合金元素、晶界类型以及残余应变的分布，并对比了整个焊接接头不同厚度上的组织和性能。研究结果表明焊缝深度方向上组织和硬度没有显著差别，底焊位置出现一层因动态再结晶形成的细小等轴晶，在316L母材热影响区（HAZ）内残余应变较焊接件其他位置高，熔合线附近具有复杂的微观结构、显微硬度、晶界类型、元素成分和残余应变分布。TEM和MFM分析表明母材316L基体内有富Cr、Mo元素的颗粒状析出相，SKPFM的结果显示该析出相伏打电势较基体更负，因而更不耐腐蚀。析出相的形成原因以及对安全端耐蚀性能的影响，尤其是对应力腐蚀（SCC）敏感性的影响有待进一步研究。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用电子背散射衍射技术 (EBSD) 和显微硬度 (HV) 测量技术，表征了原始态、锻造固溶处理态和锻造去应力处理态316LN不锈钢 (316LNSS) 的显微组织和残余应变。利用U型弯曲应力腐蚀评价方法，研究了3种材料在325 ℃、3.5%NaOH溶液中的应力腐蚀开裂 (SCC) 行为的差异。结果表明，原始态316LNSS的SCC数量最多，裂纹扩展速率最大，而锻造固溶处理态316LNSS的SCC敏感性最低；原始态和锻造固溶处理态的316LNSS在高温碱性溶液中发生明显的沿晶应力腐蚀开裂 (IGSCC)，而锻造去应力态的316LNSS发生混合型SCC；去应力处理不能有效消除锻造过程中可能产生的条带组织，不利于316LNSS整体抗SCC性能的提高。
Hits
Hits
Downloads
Comment