Alloys In High Temperature Water Research Articles

Nb speciation and microstructural characterization of the oxide layer formed on neutron-irradiated Zr-2.5 Nb alloy in high-temperature water

It is crucial to understand the degradation mechanisms of the alloy Zr-2.5 Nb, which make the pressure boundary in Canada Deuterium Uranium reactors. In the present study, Zr-2.5 Nb coupons were exposed for 567 days at 325 °C with and without neutron-irradiation in simulated primary water chemistry. A combination of scanning/transmission electron microscopy with energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy was used to investigate the base metal and oxide. The obtained results suggest that the distribution of nanopores and the variation in Nb oxidation state likely create a gradient in the oxygen concentration and electrochemical potential through the film.

Titanium oxo-hydroxo complexes as precursors of protective oxide films on the surface of titanium alloys in high-temperature water

Titanium oxo-hydroxo complexes as precursors of protective oxide films on the surface of titanium alloys in high-temperature water

Composition and morphology of oxide films formed on PT-7M titanium alloy in high temperature water

Composition and morphology of oxide films formed on PT-7M titanium alloy in high temperature water

Influence of Ammonia on the Corrosion Behavior of a Zr–Sn–Nb Alloy in High Temperature Water

Corrosion behaviors, microstructures of oxide films, and hydrogen absorptions of a Chinese domestic Zr alloy in 6.7 × 10−3 mol/L ammonia solution and 2.9 × 10−4 mol/L LiOH+9.3 × 10−2 mol/L H3BO3 solution at 360 °C, 18.6 MPa were studied. Weight gains, oxide film thicknesses, and hydrogen absorptions showed that the corrosion rate in the ammonia solution is a little higher than that in the boron–lithium solution. There is no significant difference in the microstructure and crystalline structure between the oxide films formed in the two types of solutions. The element distributions along the depth direction of the oxide films showed the existence of nitrogen in the oxide film formed in ammonia solution. Moreover, nitrogen was found to be segregated in local areas in a range of about 2 μm from the oxide/metal interface. The corrosion behavior of the Chinese domestic Zr alloy in 360 °C aqueous solution shows no difference with other Zr alloys.

The effect of dissolved oxygen respectively dissolved hydrogen on corrosion behavior of CuCrZr alloy in high temperature water

• Corrosion of CuCrZr in high temperature water with dissolved O 2 and H 2 was studied. • Sample in water with dissolved O 2 showed highest weight loss. • Sample in water with dissolved H 2 showed smallest weight loss. • Pure copper precipitates found on sample surface tested in water with dissolved H 2. • H 2 might reduce dissolved copper ions back to atoms, atoms then return to surface. In Japan Demonstration fusion reactor, the divertor plays a critical role for it helps sustaining plasma shape and hence demanding high requirements on its structural materials for the cooling system. CuCrZr alloy is considered as one of candidates and would be used in one independent cooling system. Proposals of operating conditions would be similar with fission light water reactor, where experiences have shown that water chemistry significantly influences corrosion behavior. Available references on the corrosion of CuCrZr also address the importance of water chemistries. Because the design proposal could be one of proposals towards reactor, it is worthwhile an investigation to understand the corrosion behavior of CuCrZr alloy under high temperature water environments. This work aims at the effect of dissolved oxygen, and dissolved hydrogen on corrosion behavior. Tests were conducted in an autoclave with relatively static water flow. Three different water chemistries: water with dissolved oxygen 100 ppb, water with dissolved hydrogen 1600 ppb and degassed water were chosen. The exposure time of CuCrZr coupons was 100 hr. Results showed that specimens in water with oxygen 100 ppb had highest weight loss with light-reflecting, grain-oriented surface while in water with hydrogen 1600 ppb had lowest weight loss with tarnished surface and nanoscale pure copper precipitates attached. It is believed that hydrogen reduced dissolved copper ions back to copper atoms; atoms returned to surface in precipitate forms hence reducing weight loss.

Uniform corrosion behavior of FeCrAl alloys in borated and lithiated high temperature water

The uniform corrosion behavior of model FeCrAl alloys as well as commercial Zircaloy-4 as reference material were investigated in 360 °C borated and lithiated water. The results reveal that FeCrAl alloys exhibited better corrosion resistance than Zircaloy-4. It is found that the oxide films formed on the FeCrAl alloys are composed of outer Fe3O4 layer, inner layer consisting of compact spinel layer and porous spinel layer, and transition layer containing Al-Cr-rich oxides and matrix enriched with Fe°. The spinel oxides in the inner layer are FeFe2-x-y-zCrxAlyMozO4. The corrosion mechanism of FeCrAl alloys in high temperature water is discussed.

The corrosion behavior of M5 (Zr–1Nb-0.12O) alloy in 360 °C water with dissolved oxygen

The corrosion behavior of M5 alloy in 360 °C/20 MPa water with 1.5 ppm dissolved oxygen (DO) was studied. The test was conducted by using a circulating autoclave loop system. The results indicated that DO accelerated the corrosion of M5 alloy in high temperature water. The corrosion behavior of β-Nb phase in the barrier layer and the post-transition layer in oxygenated water is completely different from that in deoxygenated water. For materials exposed to oxygenated water, β-Nb phases are sequentially oxidized to crystalline NbO (Nb2+) and crystalline NbO2 (Nb4+), then part of it is completely oxidized to Nb2O5 (Nb5+) in the barrier layer. In the post-transition layer, these crystalline oxidation products of β-Nb phase change to amorphous state, wherein Nb is totally oxidized to Nb5+ state. In the outer layer, the dissolution of β-Nb oxide is not completed when exposed to oxygenated water for even 100 days. Oxygenated water can accelerate corrosion of β-Nb SPPs, which could be responsible for high corrosion rate of Nb-containing Zr alloy in DO water.

UV induced oxide deposition on zirconium alloys in high temperature water

Abstract The effect of UV irradiation on the oxidized zirconium surface during high temperature water corrosion was investigated in both static and flowing conditions. Iron oxide deposits were found to form only on the UV irradiated surfaces. The formation of these deposits resulted from the UV illumination, which induces photo-electrochemical processes at the surface, involving Fe cations dissolved in the electrolyte. Under the high temperature conditions, photo-electrons reduce soluble Fe cations, leading to the deposition of Fe oxide on the ZrO2 surface. The UV irradiation was found to form these depositions in conditions relevant to in-reactor and could induce CRUD nucleation.

Effect of micro-arc oxidation on fretting wear behavior of zirconium alloy exposed to high temperature water

Flow-induced vibrations can result in fretting wear damage to the surfaces of clad fuel rods (tubes) against their supports in nuclear power plants. One possible solution to this problem is using oxide coatings. In this work, tangential fretting wear experiments were carried out in simulated primary cooling water such as that used in a pressurized water reactor (PWR) to study the effects of micro-arc oxidation (MAO) on the fretting wear behavior of a reactor-grade zirconium alloy known as ZIRLO™. The results indicated that the micro-arc oxidation improved the fretting wear resistance of the ZIRLO™ tube. The synergic effects of corrosion and mechanical wear on the fretting wear of the ZIRLO™ substrate and the MAO coating are discussed, and the role of the MAO coating in mitigating the fretting wear of zirconium alloy in high temperature water is revealed.

DK/da effects on the SCC growth rates of nickel base alloys in high-temperature water

The effect of dK/da on crack growth behavior of nickel base alloys has been studied by conducting stress corrosion cracking tests under positive and negative dK/da loading conditions on Alloys 690, 600 and X-750 in high temperature water. Results indicate that positive dK/da accelerates the SCC growth rates, and the accelerating effect increases with dK/da and the initial CGR. The FRI model was found to underestimate the dK/da effect by ∼100X, especially for strain hardening materials, and this underscores the need for improved insight and models for crack tip strain rate. The effect of crack tip strain rate and dK/dt in particular can explain the dK/da accelerating effect.

Effects of dissolved hydrogen on the crack-initiation and oxidation behavior of nickel-based alloys in high-temperature water

The effects of dissolved-hydrogen concentration on the formation of oxide films on Alloy 182 were investigated, along with the crack-initiation time. Results from both in-situ Raman analyses and ex-situ electron microscopy analyses indicated that NiO formed at lower dissolved-hydrogen concentrations as the NiO Raman peak decreased, whereas Cr2O3 peak and spinel oxide peaks appeared as the dissolved-hydrogen concentration increased. Crack-initiation testing showed that the crack-initiation time decreased as the dissolved-hydrogen concentration increased. The stable and thick NiO could act as a barrier to ion diffusion, and may increase the crack-initiation time of nickel-based alloys.

The effects of strain rate and carbon concentration on the dynamic strain aging of cold rolled Ni-based alloy in high temperature water

The effect of strain rate on dynamic strain aging of cold-rolled Ni-based alloy was investigated. With decreasing strain rate, the stress amplitude of serrations first increased and then saturated. Compared with the solution-annealed condition, the thermally-treated condition produced smaller stress amplitudes that saturated at a lower strain rate. Observations are consistent with a mechanism in which the locking strength of solute atmospheres first increases with increasing solute atom arrival at dislocations and gradually saturates as solute reaches a critical level.

Modeling the Effects of Dissolved Hydrogen, Temperature, pH, and Global Stress on Stress Corrosion Cracking of a Cr-Ni Model Alloy in High-Temperature Water

As an extension of recently presented stress corrosion cracking (SCC) models for pure nickel and iron in high-temperature water, the anodic path, hydrogen-assisted stress corrosion cracking of a model Cr-Ni alloy is presented, utilizing Alloy 600 (UNS 06600) mechanical properties. With the local anodic path corrosion as the crack initiation phase, the respective oxides precipitate while the crack tip solution acidify and establish local hydrogen ion reduction conditions. Depending on the applied global stress, local plastic straining then provides an active crack tip surface that transfers atomic hydrogen to the plastic zone ahead of the crack tip. Hydrogen-assisted crack propagation is then controlled by the calculated local hydrogen ion reduction charge and the plastic strain distribution ahead of the crack tip. The results show that for global stress levels close to the yield stress and at constant dissolved oxygen contents, the increasing dissolved hydrogen contents provide peak crack growth rates at ...

Photoelectrochemical study on semiconductor properties of oxide films on Alloy 600 in high temperature water with ZnO addition

Zinc addition is widely used in the primary circuit of BWR and PWR to lower radioactive adhesion of nickel base alloys. The oxide films on nickel base alloys in high temperature water indicated a duplex structure with semiconductor property. The semiconductor properties of the oxide films on Alloy 600 are changed by 650ppb ZnO addition into the high temperature water by photoelectrochemical responses investigation. A compact structure oxide with formula ZnyFexNi1−x−yCr2O4 of the outer layer, besides the chromium enrichment of the inner layer, of the oxide film on Alloy 600 in high temperature water with 650ppb ZnO addition is investigated. The semiconductor properties of the oxide films on Alloy 600 in high temperature water with 650ppb ZnO addition suggest an untypical n-type semiconductor at anodic polarization with a negative movement of the flat band potential to the oxide films on Alloy 600 without ZnO addition.

THE BEHAVIOR OF SOLUBLE METALS ELUTED FROM Ni/Fe-BASED ALLOY REACTORS AFTER HIGH-TEMPERATURE AND HIGH-PRESSURE WATER PROCESS

The behavior of heavy metals eluted from the wall of Ni/Fe-based alloy reactors after high-temperature and high-pressure water reaction were studied at temperatures ranging from 250 to 400 o C. For this purpose, water and cysteic acid were heated in two reactor materials which are SUS 316 and Inconel 625. Under the tested conditions, the erratic behaviors of soluble metals eluted from the wall of Ni/Fe-based alloy in high temperature water were observed. Results showed that metals could be eluted even at a short contact time. The presence of air also promotes elution at sub-critical conditions. At sub-critical conditions, a significant amount of Cr was extracted from SUS 316, while only traces of Ni, Fe, Mo and Mn were eluted. In contrast, Ni was removed in significant amounts compared to Cr when Inconel 625 was tested. It was observed that eluted metals tend to increased under acidic conditions and most of those metals were over the limit of WHO guideline for drinking water. The results are significant both on the viewpoint of environmental regulation on disposal of wastes containing heavy metals, toxicity of resulting product and catalytic effect on a particular reaction.

Focussed ion beam sectioning for the 3D characterisation of cracking in oxide scales formed on commercial ZIRLO™ alloys during corrosion in high temperature pressurised water

Using FIB sectioning and reconstruction techniques we have performed a quantitative analysis on the microstructure of cracks and the topography of the metal–oxide interface in oxides formed on ZIRLO™ alloys in high-temperature water. The most significant observation is the continuous production of cracks both before and after the transition in kinetics, not a sudden burst of crack nucleation at transition as assumed in the literature. By concluding that cracks are not generated as a result of the transition and are not the primary cause, we suggest that a process by which cracks within the scale become connected to the oxidising environment through interconnected nanoporosity may be critical in controlling the overall rate of oxidation.

Formulating stress corrosion cracking growth rates by combination of crack tip mechanics and crack tip oxidation kinetics

A theoretical equation for stress corrosion crack growth rate of austenitic alloys in high temperature water is reformulated based on crack tip asymptotic fields and crack tip transient oxidation kinetics. A general oxidation kinetic law is introduced, emphasizing the role of mass transport through solid oxide film at the crack tip. The effects of several parameters on crack growth rate are evaluated. The results are compared with available experimental data and other equations. A good prediction of the effect of K on stress corrosion cracking growth rate of typical austenitic alloys in simulated light water reactor environments has been achieved.

Effects of Hydrogen on Stress Corrosion Crack Growth Rate of Nickel Alloys in High-Temperature Water

Abstract Stress corrosion cracking (SCC) of Alloy 600 (UNS N06600) and Alloys 182 (UNS W86182), 132 (UNS W86132), and 82 (UNS N06082) weld metals in high-temperature water is important because thes...

Stress Corrosion Cracking of Stainless Steels and Nickel Alloys in High-Temperature Water

Abstract Stress corrosion cracking (SCC) studies in stainless steels and nickel alloys reveal that all grades and conditions are susceptible to SCC in high-temperature water, whether deaerated or aerated, high H2 or low, theoretical purity water or buffered/contaminated, lower temperature or higher. However, the kinetics of SCC growth vary enormously with stress intensity, yield strength, sensitization, water chemistry, irradiation, temperature, etc. The role of yield strength is especially important because it changes with surface cold work, bulk cold work, weld shrinkage strain, and irradiation hardening; the role of metallurgical strengthening mechanisms, e.g., nitrogen additions or precipitation hardening, may have a similar effect. SCC growth rate measurements were performed in high-temperature water on unsensitized stainless steels (and Alloy 600 [UNS N06600]) of various grades and compositions. Little effect of grade/heat of stainless steel, martensite content, or H2 fugacity/permeation rate was ob...

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.