Electrochemical methods to detect susceptibility of Ni-Cr-Mo-W alloy 22 to intergranular corrosion

Alloy 22 (UNS N06022), a Ni-Cr-Mo-W based alloy, is a candidate material for the outer wall of nuclear waste package (NWP) containers. Even though the alloy is highly stable at low temperatures, it could undergo microstructural changes during processing such as welding and stress relieving. Formation of topologically close-packed (TCP) phases such as μ, P, σ, etc. and Cr-rich carbides could make the material susceptible to localized corrosion. Hence, it is important to correlate the microstructural changes with the corrosion resistance of the alloy by nondestructive and rapid electrochemical tests. In this investigation, different electrochemical test solutions were used to quantify the microstructural changes associated with aging and welding of the wrought alloy 22. The results of double-loop (DL) electrochemical potentiodynamic reactivation (EPR) tests in 1 M H₂SO₄+0.5 M NaCl+0.01 M KSCN solution indicated Cr depletion during initial stages of aging of wrought alloy 22. Results of EPR tests in 2 M HCl+0.01 M KSCN solution at 60 °C correlated well with the Mo depletion that occurred near TCP phases formed during aging of both weld and wrought alloy 22 materials. The EPR test results were compared with standard chemical weight loss measurements specified by ASTM standard G-28 methods A and B.     

淬火介质对2519铝合金抗晶间腐蚀性能的影响

2519铝合金热轧板在530℃下保温2 h后,分别于室温(20℃)水、机油和空气中淬火,经10%冷轧变形后,于180℃进行人工时效。通过显微硬度测试、金相显微镜和透射电镜观察以及动电位极化曲线的测试,研究淬火介质对2519铝合金抗晶间腐蚀性能的影响。结果表明:经空气淬火的合金晶界析出第二相,晶界析出相粒子粗大,呈不连续分布,无沉淀析出带宽度为130 nm,晶间腐蚀深度为300μm;经室温水淬和机油淬火并时效后,晶界上的析出相尺寸较小,呈链状分布,无沉淀析出带宽度分别为20 nm和30 nm。经室温(20℃)水淬火的合金未发生晶间腐蚀,经机油淬火的合金只发生局部点蚀,说明经室温水淬的合金比经空气和机油淬火的合金时效后具有更好的抗晶间腐蚀性能。     

RA330合金的耐高温腐蚀性能

RA330合金是镍铁铬系耐热合金,用于制作煤气加热炉隔热墙。在850℃,连续运行2 160h后,通过分析其表面氧化模式,研究了其在高温下的腐蚀性能。结果表明,其与煤接触表面主要是煤灰分形成的熔盐腐蚀,氧化膜不完整,表面形成蚀坑;与煤气接触表面主要是高温氧化腐蚀,氧化膜较完整,硫腐蚀不明显。     

碳含量对C-276合金组织及晶间腐蚀敏感性的影响

选取不同碳含量的C-276合金板材样品,先对样品进行固溶处理,随后在900 ℃下进行不同时间的敏化处理。采用ASTM G28中A法,对固溶及敏化后的C-276样品进行晶间腐蚀敏感性试验,得出C-276材料的晶间腐蚀年腐蚀率随敏化时间的增加而增加,即延长敏化时间会增加C-276合金的晶间腐蚀敏感性。固溶状态下,高碳型C-276合金晶间腐蚀敏感性高于低碳型C-276合金;而在900 ℃敏化30 min以后,低碳型C-276合金呈现出更高的晶间腐蚀敏感性。采用金相显微镜和扫描电镜（SEM）研究碳含量对C-276合金显微组织的影响,固溶态下,低碳型合金晶界和晶粒内部均未发现有明显析出相,而高碳型C-276合金在部分晶界和晶粒内部分布着颗粒状富含Mo的析出相μ相。敏化过程中,无论低碳还是高碳型C-276合金,其析出相均为富含Mo的M6C型碳化物。高碳型C-276合金中,由于μ相对Mo元素起到钉扎作用,导致富含Mo的碳化物析出速度减缓,因此在敏化后,高碳型C-276合金具有更低的晶间腐蚀敏感性。      

固溶温度对Al-Zn-Mg-Cu系铝合金组织与应力腐蚀的影响

对7B50铝合金热轧板在460～490℃范围内进行固溶处理、室温水淬及人工时效,通过室温力学性能测试、慢应变速率拉伸实验及电导率测试,结合光学显微镜,扫描电镜和能谱分析,研究固溶温度对Al-Zn-Mg-Cu铝合金组织与应力腐蚀的影响。结果表明,提高固溶温度能有效减少残留相,增加再结晶的体积分数。当固溶温度从460℃提高到490℃时,屈服强度(σ0.2)和抗拉强度(σb)分别提高20.9%和23.5%,固溶温度从480℃升高到490℃时,强度变化不大,但随着固溶温度升高,伸长率先提高后降低,抗应力腐蚀性能先升高后降低。当固溶温度为480℃时,应力腐蚀敏感性最低,综合性能较好。残留相增多和再结晶程度提高是引起应力腐蚀敏感性提高的主要原因。在腐蚀溶液中,应力腐蚀断口形貌为典型的沿晶断裂。     

The effect of processing and microstructure development on the slip and fracture behavior of the 2.1 wt pct Li AF/C-489 and 1.8 wt pct Li AF/C-458 Al-Li-Cu-X alloys

Although Al-Li-Cu alloys showed initial promise as lightweight structural materials, implementation into primary aerospace applications has been hindered due in part to their characteristic anisotropic mechanical and fracture behaviors. The Air Force recently developed two isotropic Al-Li-Cu-X alloys with 2.1 wt pct Li and 1.8 wt pct Li designated AF/C-489 and AF/C-458, respectively. The elongation at peak strength was less than the required 5 pct for the 2.1 wt pct Li variant but greater than 10 pct for the 1.8 wt pct Li alloy. The objectives of our investigations were to first identify the mechanisms for the large difference in ductility between the AF/C-489 and AF/C-458 alloys and then to develop an aging schedule to optimize the microstructure for high ductility and strength levels. Duplex and triple aging practices were designed to minimize grain boundary precipitation while encouraging matrix precipitation of the T₁ (Al₂CuLi) strengthening phase. Certain duplex aged conditions for the AF/C-489 alloy showed significant increases in ductility by as much as 85 pct with a small decrease of only 6.5 and 2.5 pct in yield and ultimate tensile strength, respectively. However, no significant variations were found through either duplex or triple aging practices for the AF/C-458 alloys, thus, indicating a very large processing window. Grain size and δ′ (Al₃Li) volume fraction were determined to be the major cause for the differences in the mechanical properties of the two alloys.     

Effect of the quenching temperature on the structure and deformation mechanism of a VT22I alloy

The effect of the temperature of heating for quenching on the phase composition, structure, and deformability of a high-strength VT22I titanium alloy is studied. After quenching from a critical temperature or above, an unstable β phase forms in the structure of the alloy; upon further deformation up to 3%, this phase transforms into the α” martensite. This process occurs at low stresses (150–200 MPa) and is characterized by an increase in the internal friction of the material, which is related to the high mobility of interfacial and twin boundaries of β-phase and martensite crystals. In VT22I alloy samples quenched from below the critical temperature, a mechanically stable β phase forms; it is deformed according to a slip mechanism at sufficiently high stresses (550 MPa).     

非晶纳米Ni-P/PTFE合金镀层的晶化动力学及耐蚀性能

在化学镀Ni-P溶液中添加纳米聚四氟乙烯(PTFE)颗粒,沉积获得磷含量为9%(质量分数)的高磷NiP/PTFE合金镀层,以考察该合金的晶化动力学特性及其耐腐蚀性能。综合单晶X射线衍射及差热分析(DSC)的结果表明,获得的镀层结构为非晶态与纳米晶的混合结构,较非晶态合金的晶化活化能低。纳米PTFE颗粒的存在可能提高了该结构合金的晶化温度。热处理后的Ni-P/PTFE合金的耐腐蚀性能增强与其所形成的钝化膜有关。     

高湿热海洋环境低合金结构钢腐蚀研究进展

 21世纪是海洋的世纪,发展海洋工程材料、建设海洋工程强国是推进和实施国家海洋战略的重要内容。南海是中国海上战略要地,也是建设“海上丝绸之路”十分突出的战略支点,具有重要的战略意义。南海海洋环境是一个复杂多变的环境,不同的海域、不同的腐蚀区域、不同的材料所对应的腐蚀行为与机理都不尽相同。而南海高温、高湿的极端环境相较其他海域更为恶劣,对材料的腐蚀行为具有较大的影响,对低合金结构用钢的寿命和可靠性提出了更高要求,对于高湿热海洋环境下低合金船体结构用钢研究的重要性日益凸显。主要介绍了南海高湿热环境下船体结构用钢的耐蚀性评价方法与耐蚀性改进方法。耐蚀性评价方法包括以周浸试验为主的模拟腐蚀加速试验与相关性分析,提出了目前针对南海高湿热环境的模拟腐蚀加速试验在腐蚀介质、温度、湿度、试样尺寸等试验参数设置不统一的问题,阐述了灰关联度分析法、秩相关系数法及神经网络模型等相关性分析方法。耐蚀性改进方法包括合金成分优化、夹杂物改性与组织调控等,总结了Ni、Cr、Cu、Sb、Sn等耐蚀合金元素在高湿热环境下对材料腐蚀行为的影响及作用效果,提出了夹杂物改性方法与微观组织调控在南海环境应用的可能性。为高湿热海洋环境船体结构用钢的后续研究和实际应用提供参考。     

Choice of quenching temperature and its effect on the structure and properties of a high-strength grade 01979 aluminum alloy

Differential scanning calorimetry data are presented for the 01979 alloy produced by granular technology. The optimum quenching temperature is confirmed. Strengthening phases dissolve most completely at this temperature. The phase composition of the high-strength aluminum alloy is studied using scanning microscopy and electron microprobe analysis. The AlCu₄, AlCr₂, and MgZn₂ phases and their interplanar spacings are determined.     

Effect of copper ion implantation on corrosion morphology and corrosion behavior of LaFe_（11.6）Si_（1.4） alloy

The morphology analysis and electrochemical method were used to study the corrosion behavior of LaFe11.6Si1.4 alloy of copper ion implantation. X-ray photoelectron spectroscopy (XPS) and atomic emission spectroscopy (AES) research results showed that a 15 nm-thick oxide film was formed on the surface of sample, and the copper content reached the highest value at 60 nm with a normal distribution. Immersion experiments indicated that the corrosion happened in the copper-poor zone firstly and a galvanic connection was formed among different zones on the surface due to the inhomogeneous distribution of copper. Electrochemical experiment results showed that the corrosion was serious when the ion acceleration voltage increased, and the high acceleration could reduce the thermodynamic performance of corrosion of LaFe11.6Si1.4 alloy.     

Tensile properties of a 2014 aluminum alloy in the temperature range 250° to 500 °C

The effect of deformation temperature in the range 250° to 500 °C on the tensile ductility of a 2014 aluminum alloy was measured in constant extension-rate tensile tests, generally with an initial strain rate of 2.6 X 10^-3 s^-1. Elongation at fracture increased with increasing temperature in the range 250° to 450 °C, reaching a maximum value of ~180 pct, but in stretching above ~450 °C ductility was reduced by void growth. Below ~350 °C the limiting elongations of solution-treated sheets were much inferior to those of annealed samples. Relatively poor performance in the solution-treated condition was associated with rapid hardening during the first few percent extension followed by overaging at higher strains. When solution-treated sheets were stretched above 400 °C, recovered structures and precipitation on a coarse scale developed at an early stage of straining and the stretching limits were not much inferior to those of annealed sheets at temperatures above 400 °C. The results are discussed in terms of the contributions made to necking resistance by rate-dependent and strain-dependent components of flow strength.     

Punch-stretching behavior of a 2014 aluminum alloy in the temperature range 250° to 500 °C

The influence of forming temperatures in the range 250° to 500 °C on the performance of a 2014 aluminum alloy in punch stretching has been investigated. In tests at moderate strain rates within the 250° to 450 °C range, the biaxial stretching limits of annealed sheets were greatly superior to the room-temperature values. Limiting depths of pressing increased with increasing temperature in the range 250° to 400 °C as a result of improvement in both limit strains and strain distribution, but increasing deformation temperature above ~400 °C caused the limit strains to decrease as a result of cavitation at high strains. Under comparable conditions of temperature and extension rate, such cavity growth was more rapid in equibiaxial stretching than in uniaxial or plane-strain stretching. At 500 °C with a punch speed of 0.083 mm s^-1, the thickness strain which could be applied in biaxial stretching without significant cavitation damage was less than 0.4. Thus, susceptibility to cavitation imposes an important restriction on opportunities for combining solution treatment with a hot stretch-forming operation when using an alloy based on Al-4 pct Cu.     

The effect of potential and aging on the Pb-assisted stress corrosion cracking susceptibility of alloy 22 gas tungsten arc-welded weldments

The susceptibility of as-received, solutionized, and short-term thermally aged mill-annealed (MA) and gas tungsten arc-welded (GTAW) alloy 22 to Pb-assisted stress corrosion cracking (PbSCC) was evaluated in supersaturated, deaerated, acidic PbCl₂ solutions at 95 °C. Anodic polarization tests in acidic PbCl₂ solutions showed that 16,000 ppm of Pb produced a strong anodic peak and an order of magnitude greater passive current density for both MA and GTAW alloy 22 as compared to pure NaCl solutions. Current spikes were also observed in the anodic polarization plots for the PbCl₂ solutions, suggesting periodic events of passivity breakdown and repassivation. Constant deformation SCC tests were conducted using double U-bend samples of as-received, solutionized, and thermally aged MA and double U-groove welded alloy 22 plates. The results indicate that as-received, solutionized, and thermally aged MA and GTAW alloy 22 were resistant to PbSCC in supersaturated PbCl₂ solutions at 95 °C, pH 0.5, and applied potentials near the anodic peak ranging from −100 to 50 mV_SCE. Enhanced dissolution of alloy 22 was also observed in the crevice region of the double U-bend samples tested in the 16,000 ppm PbCl₂ solutions. This Pb concentration is seven orders of magnitude greater than that found in the anticipated repository environments, and chemical speciation modeling showed that Pb²⁺ is strongly immobilized in J-13 Yucca Mountain waters through the precipitation of PbCO₃ solids. Therefore, although enhanced dissolution of the inner U-bend did occur in our tests, the overall results from this PbSCC investigation suggest that as-fabricated, solutionized, and aged MA and GTAW alloy 22 are resistant to SCC in extremely aggressive, acidic, and supersaturated PbCl₂ solutions at 95 °C. Provided that these high Pb concentrations are not attainable in the anticipated repository environments, alloy 22 is unlikely to be susceptible to SCC, localized corrosion, and enhanced dissolution by the presence of Pb. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

S/N curve variations of polycrystalline zinc due to temperature and grain size

Pure polycrystalline zinc specimens of varying grain size and pronounced texture were fatigued at different temperatures from 125°C (T _m = 0.57) to −196°C (T _m = 0.11). Conventional S/N curves were obtained under temperature and grain size conditions which rendered the specimens ductile in tension, and unconventional, shallow-slope, S/N curves were obtained when the specimens were brittle. Marked grain size effects appeared for the unconventional fatigue results with the finer grain sizes being superior. The larger grain sizes were stronger at higher endurances at 125°C. As-machined specimens possessed a deformed, twinned surface layer, the depth of which increased with increasing grain diameter, and were, in general, slightly superior to the electropolished specimens. Tensile tests revealed that, for brittle specimens, the fracture stresses were in the vicinity of the fatigue stresses obtained when the unconventional S/N curves were extrapolated to 10° cycles. Twinning occurred in tension at higher temperatures and its extent increased with increase in grain size and temperature. The twinning stress at the first significant load drop was substantially constant at different temperatures for the same grain size but decreased with increasing grain size. The experimental results are primarily dependent upon the texture; and qualitative explanations are given for the grain size effects observed, with various types of S/N curves obtained, and the twinning phenomena.     

不同结构炭/炭复合材料的低温氧化特性

广泛应用于航空航天领域的炭/炭复合材料,主要缺点在于其与基体结构密切相关的抗低温氧化能力差。因而采用针刺整体毡作增强体,对具有不同基体炭结构的C/C复合材料在静态空气中的低温变温氧化特性和流动氧气气氛中的低温恒温氧化特性进行了实验研究,并结合材料的金相显微结构及氧化后的显微组织,对其氧化性能进行了分析。结果表明:在1000℃以下的有氧条件下,无论是变温氧化试验还是恒温氧化试验,以树脂炭为基体的C/C复合材料氧化性能均优于具有典型带状结构热解炭和树脂的混合基体C/C复合材料,且氧化优先从材料各类界面、孔隙和缺陷处开始。