Alloys In High Temperature Water Research Articles

Development of an in situ Raman spectroscopic system for surface oxide films on metals and alloys in high temperature water

In order to directly analyze the structure of oxide films on metals and alloys in high temperature water conditions, an in situ Raman spectroscopic system has been developed, utilizing Ar-laser with sapphire/diamond window assemblies as a part of an Alloy 690 autoclave. The performance of the developed in situ Raman spectroscopic system was verified using high purity NiO, NiFe 2O 4, Cr 2O 3, and NiCr 2O 4 powders. Obtained reference Raman spectra in room temperature air environment agreed well with published results. The developed Raman system has been applied for the characterization of the surface oxide films of a nickel-base Alloy 600 in typical primary water conditions of pressurized water reactors (PWRs); water with 1000 ppm boron and 2 ppm lithium at a pressure of 18 MPa and temperatures ranging up to 350 °C. In situ Raman spectra were collected for Alloy 600 in PWR water conditions at different temperatures up to 350 °C, while the specimens were heated and then cooled. In this study, NiO, Cr 2O 3, and NiCr 2O 4 phases were observed for Alloy 600 in PWR water conditions, in reasonable agreement with earlier results of ex situ studies.

Role of irradiated microstructure and microchemistry in irradiation-assisted stress corrosion cracking

Irradiation has a profound effect on the stress corrosion cracking propensity of austenitic alloys in high-temperature water. Irradiation-assisted stress corrosion cracking (IASCC) has been well documented both in the laboratory and in service over the past two decades. Numerous studies have shown that the degree of intergranular stress corrosion cracking increases with dose. However, the microstructure is simultaneously changing in several ways (dislocation loops, voids, segregation and hardening) and, not surprisingly, they all correlate with increased cracking susceptibility. As a consequence of their simultaneous development, the attribution of IASCC to one or more of these features has been difficult to establish. Mechanisms based on each of the principal effects of irradiation in the alloy are considered. Arguments can be made in support of any one of these features as the cause of IASCC, but substantial evidence exists to refute a first order correlation. The mechanism of IASCC is more likely due to a combination of factors, or second order effects not yet considered. One such mechanism that is considered is based on the change in the deformation mode caused by the irradiated microstructure and the interaction of localized deformation bands with grain boundaries.

Localized Deformation Induced IGSCC and IASCC of Austenitic Alloys in High Temperature Water

Grain boundary properties are known to affect the intergranular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking behavior of austenitic alloys in high temperature water. However, it is only recently that sufficient evidence has accumulated to show that the disposition of deformation in and near the grain boundary plays a key role in intergranular cracking. Grain boundaries that can transmit strain to adjacent grains can relieve stresses without undergoing localized deformation. Grain boundaries that cannot transmit strain will either experience high stresses or high strains. High stresses can lead to wedge-type cracking and sliding can lead to rupture of the protective oxide film. These processes are also applicable to irradiated materials in which the deformation can become highly localized in the form of dislocation channels and deformation twins. These deformation bands conduct tremendous amounts of strain to the grain boundaries. The capability of a boundary to transmit strain to a neighboring grain will determine its propensity for cracking, analogous to that in unirradiated metals. Thus, IGSCC in unirradiated materials and IASCC in irradiated materials are governed by the same local processes of stress and strain accommodation at the boundary.

Effect of Corrosion Potential and Microstructure on the Stress Corrosion Cracking Susceptibility of Nickel-Base Alloys in High-Temperature Water

Abstract To evaluate the effect of corrosion potential on the stress corrosion cracking (SCC) initiation lifetime of nickel-base alloys, periodically unloaded uniaxial constant load (PU-UCL) tests were conducted, simulating boiling water reactor (BWR) water chemistry conditions. Utilizing the exponential distribution model for the determination of SCC lifetime, the SCC improvement factor was assessed by comparing the statistical location parameter of SCC failure time in PU-UCL tests between the hydrogen water chemistry (HWC) condition and the normal water chemistry (NWC) condition. The improvement factor larger than 10 was obtained for the moderate HWC condition, whereas it became more than 30 under the same condition when noble metals were chemically doped on the specimen surface preliminarily. The effect of microstructure on the SCC susceptibility was discussed after creviced bent beam (CBB) tests and microstructural analysis on grain boundaries. Alloy 182 (UNS W86182) with dendrite structure exhibits n...

The mode of stress corrosion cracking in Ni-base alloys in high temperature water containing lead

The mode of stress corrosion cracking (SCC) in Ni-base alloys in high temperature aqueous solutions containing lead was studied using C-rings and slow strain rate testing (SSRT). The lead concentration, pH and the heat treatment condition of the materials were varied. TEM work was carried out to observe the dislocation behavior in thermally treated (TT) and mill annealed (MA) materials. As a result of the C-ring test in 1M NaOH + 5000 ppm lead solution, intergranular stress corrosion cracking (IGSCC) was found in Alloy 600MA, whereas transgranular stress corrosion cracking (TGSCC) was found in Alloy 600TT and Alloy 690TT. In most solutions used, the SCC resistance increased in the sequence Alloy 600MA, Alloy 600TT and Alloy 690TT. The number of cracks that was observed in Alloy 690TT was less than in Alloy 600TT. However, the maximum crack length in Alloy 690TT was much longer than in Alloy 600TT. As a result of the SSRT, at a nominal strain rate of 1 × 10 −7/s, it was found that 100 ppm lead accelerated the SCC in Alloy 600MA (0.01% C) in pH 10 at 340°C. IGSCC was found in a 100 ppm lead condition, and some TGSCC was detected on the fracture surface of Alloy 600MA cracked in the 10 000 ppm lead solution. The mode of cracking for Alloy 600 and Alloy 690 changed from IGSCC to TGSCC with increasing grain boundary carbide content in the material and lead concentration in the solution. IGSCC seemed to be retarded by stress relaxation around the grain boundaries, and TGSCC in the TT materials seemed to be a result of the crack blunting at grain boundary carbides and the enhanced Ni dissolution with an increase of the lead concentration.

Cross-Sectional Sample Preparation and Analysis of Intergranular Stress Corrosion Cracks in FE-NI-CR Alloys.

Transmission electron microscopy in its modern high-resolution analytical form has great potential for elucidating mechanisms of environmental cracking in structural alloys and other materials. Apart from a few pioneering efforts, the difficulties of preparing suitable samples with the original corrosion structures preserved in narrow crack tips have limited contributions of TEM in this area. Recent work involving cross-sectional crack preparation has focused on intergranular stress-corrosion cracking of Fe- and Ni-base stainless alloys in high-temperature water. This presentation will illustrate preparation methods that have proven successful, and describe limitations of the analysis.The method for preparing cross-section samples suitable for high-resolution TEM characterization is based on earlier work by Lewis et al. It involves preparing a thin section containing cracks filled with epoxy, dimple grinding selected locations near the crack tip, and ion milling. Figure 1 schematically illustrates this method. The first step is to preserve the crack opening characteristics present under loading and protect the crack surfaces during thinning.

Mechanisms of Stress Corrosion Cracking for Iron-Based Alloys in High-Temperature Water

Abstract Stress corrosion cracking (SCC) susceptibilities of a series of iron-based alloys (IBA), including some high-purity irons, were evaluated in lithiated water at temperatures up to 300°C. Inclusion distributions in each material were established using quantitative metallography and energy dispersive x-ray analysis (EDX). Electrochemical measurements were performed to investigate film formation kinetics. Results showed the minimum potential for SCC was a function of the inclusion content. Reducing the inclusion content in IBA moved the minimum potential for SCC in the anodic direction and/or increased the temperature for the onset of cracking but did not eliminate SCC.

Crevice Corrosion of Austenitic Alloys in High-Temperature Water

Abstract Oxide film characterizations and electrochemical measurements were carried out on crevices of austenitic stainless alloys to investigate the acceleration mechanism of intergranular stress corrosion cracking (IGSCC) in high-temperature water. When the chromium concentration was sufficient, type 304 (UNS S30400) stainless steel (SS) and alloy 600 (UNS N06600) exhibited good corrosion performance in crevices, forming a chromium-enriched layer in an oxide film consisting of diiron nickel oxide (NiFe2O4). When chromium was depleted in the crevice, however, the nickel-based alloy exhibited larger weight loss and a thicker film, including nickel oxide (NiO) and NiFe2O4. The crevice environment in high-temperature water was characterized by a lower pH (one unit lower) and a lower corrosion potential (300 mV to 400 mV lower) than in the bulk water environment. There was a notable increase in the coupling anode current from the crevice to the free surface when the chromium-depleted phase was located in the...

Mechanism of Lead-Induced Stress Corrosion Cracking of Nickel-Based Alloys in High-Temperature Water

Abstract A study was undertaken to better understand the lead-induced corrosion mechanism of nickel-based alloys used for steam generator tubing materials (alloys 600 and 690 [UNS N06600 and N06690...

The mechanism of oxide film formation on austenitic stainless steels in high temperature water

The oxide layers grown on an austenitic stainless alloy in high temperature water and the repassivation kinetics of the material have been studied with respect to the film formation mechanism. Examination of the morphology and composition of oxide layers reveals a double-layer structure. The inner layer consists of a chromium-rich spinel and is covered by an outer layer of magnetite or iron-nickel spinel. An investigation of film growth after abrading samples with a corundum grinder at temperatures up to 250 °C shows that passivity is fully restored within several seconds. No significant influence of temperature can be detected. The mechanism of oxide growth is explained by applying the concepts of passivity of metals to the corrosion system studied and the major reaction sequences are outlined. Breakdown of passivity in high temperature water is related to crystallisation of the initially amorphous, thermodynamically metastable, passive film. The film grows and slowly transforms into a thick oxide layer. Consequences for other models of growth are discussed.

The effects of Pb on the passive film of Ni-base alloy in high temperature water

The effects of Pb on the passive film of Alloy 600 were investigated using polarization and immersion tests. The anodic dissolution behavior was observed using anodic polarization tests in water with up to 500 ppm of PbO at pH 4 and pH 10 at 90°C. The immersion tests were conducted at 250°C with lead concentrations of 0, 25, and 250 ppm. The chemical composition of the surface films formed after 5–10 days of immersion was analyzed by AES (Auger electron spectroscopy) and XPS (X-ray photoellectron spectroscopy). The metal ions dissolved from Alloy 600 during the immersion tests were analyzed by ICPS (ion coupled plasma spectroscopy). The results indicate that, as Pb concentration increased, the critical current densities of Alloy 600 increased at both pH 4 and pH 10. At pH 10, the outermost surface films were enriched in Cr and depleted in Ni with increased levels of Pb, but the inner layer showed the opposite trend. In solution analysis, higher concentrations of Ni were observed with increased levels of Pb, which indicates that Pb facilitates Ni dissolution. This is consistent with the analysis results of outer films by XPS. These results show that a Ni-depleted/Cr-enriched outer film and a Cr-depleted/Ni-enriched inner layer may be formed on Alloy 600 in mildly caustic water containing Pb.

粗大Ｃｒ炭化物を分散したＮｉ合金の高温水中での耐摩耗性

In order to reduce radiation exposure in nuclear plants (ABWR), Co free wear resistant alloys for rollers in FMCRD (Fine Motion Control Rod Drive) were investigated. Microstructures of conventional Ni-base alloy (WPM) and Co-base alloy were compared to get hints for improving the wear resistance of Ni-base alloys, and a developing conception, dispersing large size Cr carbides into soft Ni matrix, was obtained. The conception was confirmed to be valid by sintered Ni alloys. And then, cast Ni alloys in which less material defect could be expected than sintered Ni alloys were prepared to examine the wear and impact properties. It was known that 1.92.1C-30Cr-Ni(mass%) cast alloys showed much higher wear resistance than those of WPM and Co-base Alloy in high temperature water of 288°C, and that the absorbed energy in sharpy impact test of the cast Ni alloys was more than two times larger than those of WPM and Co-Alloy 3.

Corrosion resistance of austenitic steels and alloys in high temperature water

An ampoule corrosion tests technique is presented for making a comparative corrosion-proof estimation of austenitic steels and alloys which are candidate materials for the ITER first wall and shield blanket. Influence of Cl − on the rate and character of corrosion cracking has been determined. The dependence of time before destruction on Cl − contents was obtained by experiments in twice-distilled water at a Cl − content value of less than 0.05 mg/l. Kinetics of a corrosion crack growth has been determined by way of acoustic emission and measurement of electrical resistance. It has been revealed, that corrosion cracking of 316L and 316Ti steels in water with 100 mg/l of Cl − takes place at temperatures over 50°C. For 316L (Russian analogue), 316Ti, 08Cr18Ni10Ti (type 304), 00Cr16Ni15Mo3Nb (type 316) steels and CrNiMo-1 (42–47%Cr, 1%Mo, Ni-base) alloy corrosion long-term strength and crack-resistance characteristics were obtained. Results of tests show, that corrosion characteristics are near the same for all austenitic steels under investigation with CrNiMo-1 alloy being the exception. It was not destroyed during ampoule tests.

タングステン・カーバイドロールの腐食摩耗に及ぼす冷却水質の影響

Tungsten Carbide Cemented Rolls are widely used in hot-steel-products rolling because of good wear resistance. At the early period, small diameter ring rolls with tungsten carbide mounted on steel parts were used in finishing cantilever blocks of wire rod mills. Recently, medium diameter ring rolls and solid rolls with tungsten carbide have been used in modern intermediate stands of rod mills and stretch reducing stands of tube mills. Moreover, they have started to be applied to finishing stands in stainless section mills because of good galling resistance. But the tungsten carbide rolls is very expensive compared with the conventional cast iron rolls. To apply tungsten carbide rolls instead of cast iron rolls economically, it is necessary to get about five to ten times roll life of cast rolls. In this report, the corrosive characteristic of tungsten carbide alloy in high temperature water, which is one of main reasons for roll wear, is investigated. It was found that the optimization of the pH and calcium concentration of cooling water is effective to suppress corrosion of rolls. This effect was assured in the real production of three roll type stretch reducing stands of the tube mill in Kashima Steel Works.

Stress Corrosion Cracking Sensitivity of High Purity Fe-Cr Alloys in High Temperature Water

Stress Corrosion Cracking (SCC) sensitivities of high purity Fe-Cr alloys were investigated in simulated Boiling Water Reactor (BWR) and primary Pressurized Water Reactor (PWR) cooling waters, by constant extension rate tests (CERT) at a strain rate of 4x10 -7 s -1 . No high purity Fe-Cr alloy showed any SCC sensitivity in either simulated BWR and PWR primary water environment.

Heteropoly anions as corrosion inhibitors for aluminium in high temperature water

Corrosion of aluminium and its alloys in high temperature water (90–300°C) has been studied with and without addition of various oxotungstates by a number of methods. Substantial decrease (in some cases by 10 times) of the corrosion rate in the presence of polyoxotungstates was observed. The pitting potential was shown to shift to positive values depending on the heteropolytungstate added. According to XPS tungsten is incorporated into the surface oxide film formed during the treatment. SEM cross-sections reveal a marked decrease of the oxide film thickness in the presence of polytungstate. It is assumed that the heteropolytungstate on active site in the aluminium oxide film is preventing the recrystallization and growth protective alumina layer. Pretreatment of aluminium in solutions of heteropoly tungstates is also effective in preventing corrosion at high temperature.

ChemInform Abstract: The Effect of Chromium, Carbon, and Yttrium on the Oxidation of Nickel‐ Base Alloys in High Temperature Water.

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The Effect of Chromium, Carbon, and Yttrium on the Oxidation of Nickel‐Base Alloys in High Temperature Water

Since the surface film has been implicated in several models of intergranular stress corrosion cracking (IGSCC) of nickel‐base alloys, this study was initiated to provide a foundation for the future study of a possible link between the nature of the surface film and IG crack susceptibility. The influence of chromium, carbon, and yttrium on the nature of the surface film formed on nickel‐base alloys was investigated after 100 h of exposure in high purity, deaerated, hydrogenated water at 360°C. The chemical composition of an ultrahigh purity (UHP) alloy of Ni‐17Cr‐9Fe‐0.0030C was altered by varying the Cr content, doping with C, or ion implanting Y. X‐ray photoelectron spectroscopy and scanning transmission electron microscopy provided information on the chemical composition, structure, morphology, and thickness of the surface film. Increasing the chromium content from 5 to 17 weight percent (w/o) of a Ni‐xCr‐9Fe‐low C alloy dramatically changes the surface film from predominantly to . An additional increase in Cr from 17 to 30 w/o does not significantly alter the type, distribution, or thickness of the oxide phases formed. This suggests that there is a critical chromium concentration that controls the formation of after 100 h of exposure to high purity, deaerated hydrogenated, water at 360°C. The presence of in these alloys is attributed to the high affinity of Cr for oxygen, and the increased stability of over many other oxides in reducing environments. The addition of 300 wppm carbon to a Ni‐17Cr‐9Fe‐0.0030C alloy increases the film thickness while promoting the formation of , possibly by an increase in the diffusion of Ni or by an enhancement of the surface activity of the Ni atoms. The addition of 300 wppm carbon to a Ni‐30Cr‐9Fe‐0.0020C alloy increases the film thickness without changing as the dominant surface species. Yttrium implantation to 2.4 atom percent at a depth of 70 nm in Ni‐17Cr‐9Fe‐0.0030 and 0.030 C alloys produces a similar film thickness and similar composition profiles containing slightly more than . Yttrium is known for forming which most likely promotes the formation of by acting as nucleation sites for the similarly structured chromia.

Fracture Mechanics Data and Modeling of Environmental Cracking of Nickel-Base Alloys in High-Temperature Water

Abstract Environmental cracking of ductile nickel-base alloys has occurred both in pressurized water reactors (e.g., steam-generator tubing) and boiling water reactor components such as pressure-vessel safe ends, weld butters, and filler metals for joining nickel-base alloys or dissimilar metals, and attachment welding pads on pressure vessels. Accurate assessment of the interrelated effects of material, environment, and mechanics on environmentally assisted crack growth rates is required for life prediction of nuclear power reactor components. The objective of this study is to understand and predict the environmental cracking behavior of ductile nickel-base alloys in 288° C water. Experiments were performed on 1T CT specimens of Alloy 600 base metal, and Alloy 182 and Alloy 82 weld metals to evaluate the effects of water chemistry, heat treatment, and stress intensity on crack growth rate. Fracture mechanics, crack growth data on ductile nickel-base alloys were also thoroughly surveyed to provide an over...

Intergranular Cracking of Ni-16Cr-9Fe Alloys in High Temperature Water

Abstract The objective of this work is to provide a better understanding of the role of microstructure in intergranular stress corrosion cracking (SCC) of controlled-purity, Inconel 600-type alloys...