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The corrosion characteristics of a novel alumina-forming austenitic (AFA) steel exposed to 600 ℃/25 MPa deaerated supercritical water (SCW) were investigated. The results show that the weight gain curves of the AFA steel follow parabolic law. A chromium-rich oxide scale containing reticular alumina is formed in the AFA steel, which contributes to the high corrosion resistance of the AFA steel. No continuous alumina scale is formed on the AFA steel with 2.5 wt% Al addition, which is attributed to the negative effects of B2-NiAl, Laves and σ-FeCr precipitates on the continuity of alumina scale. • Corrosion behavior of an alumina-forming austenitic stainless steel in 600 °C SCW is investigated. • 2.5 wt% Al addition is insufficient to maintain the formation of independent alumina scale on AFA steel in 600 °C SCW. • Protective Cr/Al-mixed oxide scale is formed on AFA steel. • Effect of precipitates on the formation of alumina scale is examined. • B2-NiAl phase is not optimal for the formation of continuous alumina scale. [ABSTRACT FROM AUTHOR]

Highlights • Weight gain data of candidate cladding materials for SCWR is summarized. • ODS steels and AFA steels may be promising cladding material for SCWR. • Corrosion mitigation techniques are also reviewed. Abstract Due to increasing attentions to supercritical water reactor (SCWR), the corrosion response of materials in supercritical water (SCW) has attracted lots of research interests. This paper summarizes the current corrosion test results conducted in Shanghai Jiao Tong University (SJTU) and compares the data with literature data. The corrosion resistances of candidate materials (including ferritic/martensitic (F/M) steel, austenitic stainless steel, alumina-forming austenitic (AFA) stainless steel and oxide dispersion strengthened (ODS) steel) in supercritical water are discussed and analyzed. High Cr content austenitic stainless steel, proper Cr content AFA stainless steel and ODS steel are promising cladding materials for SCWR since they generally have satisfactory corrosion resistance even in 650 °C SCW. [ABSTRACT FROM AUTHOR]

Abstract This work compared the stress corrosion cracking (SCC) susceptibility of two austenitic alloys in supercritical water (SCW), and revealed the quantitative difference of SCC growth rates through scanning transmission electron microscopy (STEM). Results showed that in-situ sensitization and creep occurred on the specimens during the SCC tests in SCW environment. Higher degree of Cr-depletion at the grain boundary ahead of the SCC crack tip was identified in the Fe-25Cr steel specimen, which has suffered severer in-situ sensitization because of the lower Cr content than the Ni-29.3Cr alloy specimen, and this in turn increased the creep susceptibility. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The effect of frequency (5–30 Hz) on the fretting corrosion behavior of Alloy 690 tube was investigated in simulated pressurized water reactor secondary water. The results show that the wear volume of the tube increases by ∼19 times with the frequency increases, and the wear mechanism changes from adhesive wear to delamination wear and abrasive wear. The increasing fretting frequency could affect the contact temperature and accelerates the change of contact stress, which cause a shift in the wear mechanism. Under the synergic effect of mechanical wear and corrosion, a gradient multi-layer structure is formed on the wear area, which is composed of the ultra-fine grain three-body layer, the tribologically transformed structure layer and matrix distributed from top to bottom. The three-body layer is mainly composed of Fe-rich spinel oxides and a small amount of Fe 3 O 4 and Cr 2 O 3 , and its thickness increases with the increase of the fretting frequency. • The role of frequency on the fretting corrosion of Alloy 690 is investigated. • A gradient multi-layer structure forms on the wear area of the Alloy 690. • The influence of frequency on oxidation and wear damage of materials are studied. • The effects of frequency on wear mechanism of Alloy 690 are revealed. [ABSTRACT FROM AUTHOR]

The stress corrosion cracking (SCC) propagation behavior of 20% cold worked 316 L stainless steel (SS) and Alloy 690 was investigated in high-temperature oxygenated water. No discernable effect was observed at the same pH level for LiOH or KOH. Increasing pH could dramatically enhance the crack growth rates (CGRs) due to the dissolution of Cr-rich oxide film and the weakening of passivity in high pH regimes. The similarities in SCC behavior and cracking characteristics indicate that the cracking mechanism of both austenite alloys occurs by a slip-dissolution model. • The addition of dissolved oxygen and chloride shows limited effect on the stress corrosion cracking resistance of Alloy 690. • The absence of any discernable effect of KOH vs. LiOH on CGR confirms the feasibility of substituting LiOH with KOH. • Increasing pH significantly enhances the cracking of both 316 L and Alloy 690. • The cracking of both austenite alloys can be explained by the slip-dissolution model. [ABSTRACT FROM AUTHOR]

The effects of δ-ferrite on stress corrosion cracking behaviors of austenite weld metal were analyzed by a ferrite-crack model. The results show that the δ-ferrite might inhibit the crack propagation initially once the crack tip meets it by reducing the local plastic strains. Thereafter, the crack might still propagate either along the δ-ferrite boundary (intergranular, IG) or across the δ-ferrite (transgranular, TG). The IG cracking will accumulate much more plastic strains at the crack tip and tends to promote crack growth. The TG cracking might be enhanced by the oxidation-induced embrittlement of the δ-ferrite. • The mechanism understanding of δ-ferrite on stress corrosion cracking of the austenite stainless steel welds was obtained. • The increasing crack tip strain and the resultant higher crack growth rate were revealed during the intergranular cracking. • The oxidation-induced embrittlement of δ-ferrite could reduce the crack tip stress and promote the transgranular (TG) crack. [ABSTRACT FROM AUTHOR]

The cracking growth behavior of a sensitized Alloy 800H in supercritical water (SCW) was studied at temperatures between 450 °C and 550 °C. Crack growth rates (CGRs) were measured in SCW environments with various dissolved gasses and in inert argon environment to separate the effects of corrosion and creep on the overall cracking susceptibility. Creep cavities were widely observed at the grain boundaries ahead of the crack tip in both SCW and Ar gas environments. Results show that both corrosion and creep contribute to the cracking behavior of sensitized Alloy 800H, and the corrosion contribution depends on the corrosion potential of the SCW environment. The stress corrosion cracking and creep CGRs increase with temperature, and their apparent activation energies are similar. The data support the conclusion that cracking was mostly controlled by creep and oxidization at the crack tip. [ABSTRACT FROM AUTHOR]

The intergranular cracks and grain boundary (GB) network of a GB-engineered 316 stainless steel after stress corrosion cracking (SCC) test in high temperature high pressure water of reactor environment were investigated by two-dimensional and three-dimensional (3D) characterization in order to expose the mechanism that GB-engineering mitigates intergranular SCC. The 3D microstructure shown that the essential characteristic of the GB-engineered microstructure is formation of many large twin-boundaries as a result of multiple-twinning, which results in the formation of large grain-clusters. The large grain-clusters played a key role to the improvement of intergranular SCC resistance by GB-engineering. The main intergranular cracks propagated in a zigzag along the outer boundaries of these large grain-clusters because all inner boundaries of the grain-clusters were twin-boundaries (∑3) or twin-related boundaries (∑3 n ) which had much lower susceptibility to SCC than random boundaries. These large grain-clusters had tree-ring-shaped topology structure and very complex morphology. They got tangled so that difficult to be separated during SCC, resulting in some large crack-bridges retained in the crack surface. [ABSTRACT FROM AUTHOR]

The irradiation accelerated corrosion within monolayer grains of a new AFA steel exposed to sCO 2 are studied. The presence of irradiation induced dislocation loops accelerate element diffusion and reduces corrosion resistance by ∼44%. Many oxide scale features are firstly found, including a two-phase inner layer consisting of Ni-rich austenite and Cr-rich spinel, and Al 2 O 3 /SiO 2 oxide precipitates. Irradiation leads to an additional Cr-rich oxide layer at the bottom of inner layer and a narrower Al 2 O 3 band in the internal oxidation layer. Irradiation also induces Cr depletion at grain boundaries, thereby impeding the formation of a protective Cr-rich oxide scale. • Coupling effects of irradiation and corrosion of a new AFA steel exposed to sCO 2 are firstly studied. • Irradiation induced dislocation loops accelerate the element diffusion, while it is not enough to form a protective Cr 2 O 3 /Al 2 O 3 in sCO 2. • A two-phase inner layer (Ni-rich austenite + Cr-rich spinel), and Al 2 O 3 /SiO 2 oxide precipitates are formed in sCO 2. • Irradiation results in an extra Cr-rich oxide layer and a narrower Al 2 O 3 band near the O/M interface. • Irradiation induces Cr depletion at grain boundaries, then the protective Cr-rich oxide scale cannot be easily formed here. [ABSTRACT FROM AUTHOR]

The corrosion behavior of an alumina-forming duplex stainless steel with different surface treatment was investigated in supercritical carbon dioxide. The results showed that polished materials had higher weight gain than the ground ones. An unprotective multilayer oxide scale was formed above FCC phase, whereas protective and continuous Cr/Al-rich oxide layers were formed above BCC phase on polished materials. Similar protective Cr/Al-rich oxide layers were formed, regardless of the FCC or BCC phase on ground materials. Grinding leads to the faster diffusion of Cr and Al, which causes the easier formation of the continuous Cr/Al-rich oxide layers. • Corrosion behavior of a new AFDSS exposed to sCO 2 is investigated • Effect of grinding and polishing on the corrosion behavior is examined • The polished materials exhibit poorer oxidation and carburization resistance • Multilayer oxide scales containing Fe/Cr/Al are formed on polished materials • Protective Cr/Al-rich oxide scale is formed on ground materials [ABSTRACT FROM AUTHOR]

• The fretting corrosion of zirconium alloy in high temperature water is studied. • Changes in displacement or normal force affect debris movement and wear mechanisms. • A dual-layer structure oxide scale is formed on the worn area. • The integrity of the oxide layer is negatively correlated with its thickness. • Fretting wear accelerates material corrosion by debris refinement and cracking. Studying the fretting wear mechanism of zirconium alloy in high temperature high pressure water is of great importance for understanding the failure behavior of fuel assembly. In this work, the tangential fretting wear of zirconium alloy tube at different displacement amplitudes (40 µm and 80 µm) and normal forces (6 N and 12 N) was investigated in high temperature high pressure water. The results show that the wear depth and wear volume of zirconium alloy tested at 6 N-80 µm are the highest among all the tests. When the testing condition is 6 N-80 µm, the fretting is located in the gross slip regime. Oxidation and abrasive wear dominate the fretting wear behavior. The increase in normal force and decrease in displacement reduces the relative sliding distance between the contact interfaces, which reduces the ejection of wear debris and changes the wear mechanism. When the test conditions are 6 N-40 µm and 12 N-40 µm, the fretting regime is located in the partial slip regime, and the dominant wear mechanisms are adhesive wear and oxidation. Under the synergistic effect of mechanical wear and high-temperature water corrosion, a dual-layer structure oxide scale is formed on the worn area. The mixed oxide layer with loose and porous structure is formed by the accumulation of granular wear debris, while the dense inner oxide layer is mainly formed by oxidation of the matrix alloy. Fretting wear accelerates material corrosion by wear debris refinement and cracking. The integrity of the oxide layer is negatively correlated with its thickness. As the thickness of the oxide layer increases, more cracks can be observed in the oxide layer. [ABSTRACT FROM AUTHOR]

This work experimentally studied the influence of gas and liquid distribution on a semi-open mixed-flow pump performance. High speed photography technology was contributed to obtain the evolution law of bubbles in the impeller. The results show that the inlet gas volume fraction (IGVF) and liquid flow rate are the main factors affecting the performance of the pump. The pressurization capacity linearly decreases with the increase in IGVF when the liquid flow rate is close the best efficiency point. However, this factor suddenly drops when the IGVF reaches a certain critical value under the condition of a low liquid flow rate. The spatiotemporal evolution characteristics of the isolated bubbles and gas column in the segregated flow were investigated. In addition, the bubbles are evenly distributed, and the flow pattern is mainly bubbly flow (BF) or aggregated BF (ABF) in the impeller inlet area without blades. Under small liquid flow rate conditions, the bubbles tend to coalesce into larger-sized gas-pocket with an increase in IGVF. The tip leakage vortex increases the turbulence intensity of the flow field. The results show that the bubbles downstream of the tip leakage vortex in the impeller channels are more easily broken into smaller bubbles and form a BF or ABF. • The visualization experiment of mixed-flow gas-liquid two-phase pump is carried out. • Relationship between external characteristics and bubble distribution is clarified. • Gas-liquid two-phase flow patterns in the impeller of the mixed-flow pump are obtained. • The evolution process of isolated bubbles passing through the tip clearance is found. • The dynamic circulation process of air pocket in the impeller are clarified. [ABSTRACT FROM AUTHOR]

The corrosion behavior of Alloy 800H in deaerated supercritical water was investigated. Multi-pass cold rolling was used to achieve thickness reductions of up to 80%, and the weight gain vs. time (up to 1000 h) in supercritical water at 600 ℃ and 25 MPa were obtained for specimens in the polished vs. ground surface condition. Polished specimens without rolling showed the highest corrosion rates, and surface grinding or cold rolling significantly increased the corrosion resistance. A thick oxide film develops, with an outer moderately uniform layer of magnetite (Fe 3 O 4) with crystallites along the surface, and areas of uneven oxidation into the metal that incorporate Cr (e.g., FeCr 2 O 4). Very few Cr 2 O 3 particles exist, and preferentially near the grain boundaries. Continuous Cr-rich oxide films were found in the thin oxide films on the surface of ground specimens and heavily rolled specimens, and an associated Cr depleted zone in the metal under the oxide of ground specimens, but not in heavily rolled specimens. This indicates that the high density of dislocations accelerates the diffusion of elements and enhance the formation of Cr-rich oxide film, which promotes passivity. • Surface grinding and cold rolling improved corrosion resistance of Alloy 800H in SCW. • For Alloy 800H, continuous Cr 2 O 3 oxide layer only forms around grain boundaries. • A thick deformation layer can avoid the Cr-deplete in matrix under oxide film. [ABSTRACT FROM AUTHOR]

The effect of thermal aging on environmental assisted cracking (EAC) of 308 L weld metal was investigated. Experimental results reveal that thermal aging promotes corrosion fatigue (CF) crack growth with extensive inter-dendritic cracking, but has a limited effect on the stress corrosion cracking (SCC) growth under constant loads. The higher crack tip strain rate and the enhanced preferential oxidation of deteriorated δ-ferrite are responsible for the enhanced CF susceptibility after thermal aging. The dispersed δ-ferrites and the decreased crack tip strain rate account for the high SCC resistance under constant load regardless of the thermal aging. • Thermal aging causes the microstructure evolutions of d-ferrite and the resultant mechanically embrittlement of 308L weld. • The effect of thermal aging on environmental assisted cracking varies with the crack tip strain rates. • Thermal aging enhances the corrosion fatigue crack growth by about 10X and generates extensive inter-dendritic cracks. • Thermal aging up to 425°C for 4,500h has a limited effect on the stress corrosion cracking growth under constant loads. [ABSTRACT FROM AUTHOR]

[Display omitted] • Y 2 O 3 reduced the grain size and decreased the weight gain of alumina-forming austenitic oxide dispersion strengthened steel. • Al 2 O 3 layer were observed in the grain boundaries, and reduced the corrosion degree of the underlying material. • The structure in the inner layer was affected slightly by Y 2 O 3 particles. • Y 2 O 3 particles at the oxide/matrix interface caused the sunken corrosion pits, but the further development was inhibited by Al addition. A new alumina-forming austenitic oxide dispersion strengthened steel was prepared, and the general corrosion behavior was studied. The results showed that the Y 2 O 3 addition reduced the grain size. With small grains, the grain boundary density increased, which accelerated the formation of stable oxide scale in the corrosion process and obviously decreased the weight gain of AFA-ODS steel. A four-layer oxide scale was formed on the both sides of grain boundary in the inner layer, and a Cr-depletion and metallic Ni layer were formed at the oxide/matrix interface. The upper part of inner layer had many cavities. Al 2 O 3 protective layer appeared in the inner oxide layer and the corrosion degree of the underlying material was reduced. Grain boundary migration was also induced by the element diffusion. The structure surrounding Y 2 O 3 particles in the inner layer was affected slightly by Y 2 O 3 particles. Y 2 O 3 particles at the oxide/matrix interface could promote the corrosion and caused the sunken corrosion pits because the element could diffuse easily through the interface between Y 2 O 3 particles and the material. However, with the addition of Al, Al could diffuse into the sunken pits and wrapped Y 2 O 3 particles, which inhibited the further development of the sunken pits. [ABSTRACT FROM AUTHOR]

In this study, we investigated the composition, microstructure, and phase evolution of (390–430 °C for 1–30 h) 17-4PH stainless steel with a work-hardened layer in the low-temperature plasma nitriding process. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy were used for the analysis. The results suggested that crack-like structures appeared with the nitriding conditions of 410 °C for 5–30 h and 430 °C for 3–30 h. The activation energy was relatively low (32 kJ/mol) at the initial stage of nitriding due to the presence of a work-hardened layer, which increased with elevated nitriding temperature and prolonged time. The nitrided layer was mainly composed of γ′-Fe 4 N with lamellar and granular shapes, whose intensity increased with increasing nitriding temperature or time. In the case of a lower temperature (390 °C) and shorter time (1−3h) of plasma nitriding, the austenite in the work-hardened layer transformed to the S phase (expanded austenite), and α' N (expanded martensite) was formed. As the nitriding temperature or time further increased, the expansion of the α' N and S phase increased, eventually both the S phase and α′ N disappeared. The phase evolution occurred: S phase transfers to CrN in the work-hardened layer, while α′ N phase transfers to γ′-Fe 4 N or CrN, and γ′-Fe 4 N phase transfers to α + CrN in the substrate. Among these phases, α′ N was distributed next to γ′-Fe 4 N, the α phase was surrounded by γ′-Fe 4 N, and CrN was precipitated at the normal grain boundaries but not at the twin boundaries. This work can provide a theoretical basis for the investigation of the wear and corrosion properties of the nitrided material in their application domains. [Display omitted] • The interaction between the work-hardened layer and plasma nitriding is analyzed. • The phase evolution is systematically investigated by XRD and TEM. • More visual phase structure and distribution are obtained by TEM. • CrN was precipitated at normal grain boundaries but not at the twin boundaries. [ABSTRACT FROM AUTHOR]

The corrosion behavior of 310 S stainless steel with and without mechanical deformation (surface grinding and cold work) has been investigated. The experimental results show that mechanical deformation enhances corrosion resistance of materials. Multilayer oxide scale is observed on the material without mechanical deformation, which owns a loose structure and contributes to the severe carburization of the material. Thin and protective oxide scale (Cr/Mn-rich and Si-rich) is formed on the material after mechanical deformation, which hinders the internal carburization. Mechanical deformation reduces grain size and makes grain boundary diffusion become predominant, which improves the corrosion resistance of materials. [Display omitted] • Corrosion behavior of 310 S after exposed to sCO 2 has been investigated. • Mechanical deformation (cold work and grinding) enhances anti-corrosion capability. • Mechanical deformation changes the corrosion mechanism of 310 S. • Grain boundary diffusion dominates diffusion mode of the deformed materials. [ABSTRACT FROM AUTHOR]

The effect of pH on the stress corrosion cracking (SCC) initiation behavior of 20% cold worked 316 L stainless steel (SS) at constant load was investigated. No cracks initiated after 4050 h testing in 360 °C high temperature water with a pH 325 °C of 7.3, while extensive intergranular (IG) cracks initiated when the pH 325 °C was increased to 10.1. A minimum crack initiation time of 886 h was detected at 0.9 YS. Localized attack of grain boundaries (GBs) and deformation bands is considered to be the precursor of crack initiation. The mechanistic understanding of the crack initiation and propagation is discussed. • No crack initiation was detected in a 20%CW 316 L SS loaded at 0.9-1.05 YS after 4050 hours testing in high temperature water with a pH 325 °C of 7.3. • Extensive intergranular (IG) cracking was observed when the pH 325 °C was increased to 10.1. • The concentrated alkaline water facilitates the dissolution of oxide film, accelerates the film rupture and delays the re-passivation. • The crack initiation of cold worked SS is suggested to be dominated by a stress/strain driven localized corrosion mechanism. [ABSTRACT FROM AUTHOR]

Fretting corrosion of as received and shot peened zirconium alloys exposed to high temperature high pressure water is tested. High resolution characterization techniques are applied to study the microstructure and composition of the worn surface. The results show that shot peening increases the wear resistance of the material, changing the wear mode from abrasive wear plus delamination to abrasive wear. Mechanical wear promotes corrosion of zirconium alloy by forming a thick dual-layer structure oxide scale in the debris buildup area. While the effects of corrosion on the fretting wear depend on the integrity of the oxide scale. • Fretting corrosion of as received and shot peened zirconium alloy is investigated. • Shot peening increases the corrosion and fretting corrosion resistance of zirconium alloy. • Fretting wear accelerates material corrosion by oxide film peeling off and cracking. • The integrity of the oxide scale determines the effects of corrosion on the fretting wear. [ABSTRACT FROM AUTHOR]

The crack growth behavior of a cold worked alumina-forming austenitic (AFA) steel in supercritical carbon dioxide (sCO 2) and Ar is studied. AFA steel exhibits higher crack growth rates in sCO 2 than in Ar in the temperature range of 550 °C~650 °C. Creep cavities are widely observed near the crack growth paths and ahead of the crack tips on the specimens tested in both environments. Higher cavity density is observed at the crack tip of the specimen tested in sCO 2 , which is caused by oxidation and carburization. The high cavity density weakens the grain boundaries and accelerates the fracture of the materials. [Display omitted] • Cracking growth behavior of an alumina-forming austenitic steel in Ar and sCO 2 is investigated. • Higher crack growth rates obtained in supercritical carbon dioxide than in Ar. • Creep cavities are widely observed on the specimens tested in both environment. • Higher cavity density occurred on the specimen tested in sCO 2. • Oxidation and carburization promote the formation of cavities and accelerate the fracture of the material in sCO 2. [ABSTRACT FROM AUTHOR]

Solution/mill annealed Alloy 600 samples were cathodically polarized in a H 2 SO 4 solution and 300 °C water. The effect of hydrogen absorption on the microstructure and oxides of the alloys was investigated. Carbon crystallization in the polarized mill annealed alloy reduced the solubility of hydrogen in this alloy and increased its mechanical strength. Hydrogen charging on the solution/mill annealed alloys at 300 °C pure water increased the oxide thickness. Compared to the uncharged alloys, in the 300 °C hydrogenated primary coolant hydrogen modified the oxides of the solution/mill annealed alloys to a Cr-rich inner/Ni-rich outer layer and a Cr-rich outer/Ni-rich inner layer oxide, respectively. ● Hydrogen decomposed the Cr 23 C 6 carbide to form graphite in the mill annealed alloy. ● Graphitization reduced the hydrogen solubility in the mill annealed alloy. ● Graphitization improved the strength of the mill annealed alloy. ● Hydrogen solubility in Alloy 600: solution annealed > mill annealed. ● Mechanisms of oxide evolution at high-temperature solutions were introduced. [ABSTRACT FROM AUTHOR]

• Cold work reduces the corrosion resistance of Alloy 800H in supercritical water containing 200 ppb oxygen. • At initial corrosion stage, the corrosion behavior of as-received and cold-worked materials is similar. • The formation of a continuous chromia layer reduces the oxygen partial pressure at the oxide scale-matrix interface, which contributes to the later internal oxidation and selective oxidation of the elements. • With the increase of exposure time, the microstructure of the cold worked materials becomes more complicated and is further subdivided into Fe 3 O 4 /Ni x Fe 3- x O 4 /Ni x Fe y Cr 3- x - y O 4 /Cr 2 O 3 / NiO/Fe x Cr 2- x O 4 +pure Ni multi-layer structure. • Through observation of the oxidation process and the calculation of thermodynamic equilibria, the oxide scale differences were explained through the hypothesis that diffusion barriers were created by the prevailing oxides. Revealing the corrosion mechanism of materials in supercritical water (SCW) is a key issue for the development of a supercritical water reactor (SCWR). Considering cold work is inevitable in the construction of nuclear reactors and its effect on the corrosion behavior of materials in SCW is still unclear, the corrosion behavior of solution-annealed (as-received) and 30% cold-worked Alloy 800H were studied at 600 °C in aerated SCW for 1500 h. The microstructure of the oxide scale was studied by a variety of characterization techniques. The results indicate that cold work increases the corrosion rate of the materials, promotes selective oxidation and internal oxidation, and this was attributed to the high diffusion rate of different ions along "short-circuit paths". The oxide scale composition and structure of the cold-worked material, which is subdivided to Fe 3 O 4 /Ni x Fe 3- x O 4 /Ni x Fe y Cr 3- x - y O 4 /Cr 2 O 3 /NiO/ Fe x Cr 2- x O 4 + pure Ni multi-layer structure, are much more complicated than the as-received material after 1500 h exposure. Combined with the thermo-dynamic equilibrium calculation, the oxidation processes of the as-received and cold-worked materials were analyzed to reveal the effect of cold work on the corrosion behavior of Alloy 800H. [Display omitted] [ABSTRACT FROM AUTHOR]

The oxidation/carburization behavior and failure mechanism of 310S stainless steel (SS) and Alloy 800H exposed to supercritical carbon dioxide at 650 °C/20 MPa were investigated. The results show that the oxidation kinetics of 310S SS and Alloy 800H both approximately follow the parabolic oxidation law. The weight gain of Alloy 800H is higher than 310S SS for the first 2000 h exposure. While with the increase of exposure time to 3000 h, the weight gain of Alloy 800H decreases, and becomes lower than 310S SS. Cr 2 O 3 is formed on the surface of 310S SS, while a multilayer structure mainly composed of outer MnCr 2 O 4 -Cr 2 O 3 layer and inner MnCr 2 O 4 -SiO 2 layer is formed on Alloy 800H. Carburization happens in the oxidation process of 310S SS and Alloy 800H. However, the carburization performances of the two kinds of materials are different. For Alloy 800H, a C layer is deposited nearby the O/M interface, which is because that the inner MnCr 2 O 4 and SiO 2 layer in the oxide scale acts as a barrier for the inward diffusion of C-containing substances. For 310S SS, a carburized region with more and bigger carbides is formed in the matrix alloy beneath the Cr 2 O 3 layer. The oxide spallation occurs on Alloy 800H after 2000 h exposure, which explains the reason that the weight gain of Alloy 800H decreases with the further increment of testing time to 3000 h. The spallation of oxide film on Alloy 800H is likely to be attributed to the presence of the inner MnCr 2 O 4 layer, continuous SiO 2 layer and the deposited amorphous C nearby the O/M interface. [Display omitted] • The oxidation kinetics of 310S SS and Alloy 800H in 650 °C/20 MPa supercritical CO 2 approximately follow the parabolic law. • Cr 2 O 3 is formed on the surface of 310S SS. • A multilayer structure oxide is formed on Alloy 800H. • Carburization happens in the oxidation process of both materials, while spallation occurs only on Alloy 800H. [ABSTRACT FROM AUTHOR]

A local-regional power loss analysis method based on multiphase computational fluid dynamics (CFD) simulation results is proposed in this study. This method is used to investigate the energy conversion characteristics of a three-stage electric submersible pump under high inlet gas volume fraction (IGVF) conditions. Results show that the input power and effective power increase first and then decrease along the streamline. When IGVF increases from 0% to 14.5%, the total input power and total effective power decrease by 32.4% and 56.2%, respectively. In particular, the input power and effective power in R4 drop by 62% and 67%, respectively. The high gas volume fraction (GVF) area on the blade pressure surface near the impeller inlet causes the power decrease in R4. However, the input power in R6 increases by 47.5%. This condition is due to a jet flow near the impeller outlet causes the vortex and high GVF area in R6, thereby leading to a high liquid velocity area along the radial direction near the pressure surface of the impeller blade. The kinetic energy of the fluid in the jet region increases rapidly in accordance with Bernoulli equation and is converted into pressure energy in the vortex area. The total power loss increases quickly with IGVF. The power loss near the impeller outlet area at 14.5% IGVF is ten times higher than that of 0% IGVF condition and five times higher than that of 5% IGVF condition. This condition is caused by the large air pockets accompanied by vortices in the area. This work provides a theoretical basis for the design and optimization of the multiphase pump. • Local-regional power loss analysis was used in gas-liquid pump energy conversion. • Energy conversion characteristics at pump surging condition were studied. • The value of input power, effective power and power loss in the area was obtained. • The reason for the decrease of pump work capacity in the area was pointed. • Mechanism of the influence of gas volume fraction on pump work capacity is analyzed. [ABSTRACT FROM AUTHOR]

The Mg2Ni intermetallic compound was successfully prepared from magnesium and nickel nanoparticles produced by hydrogen plasma–metal reaction. Two preparation methods were developed to obtain the compound. One is heating the nanoparticles under 0.10 MPa argon pressure at 703 K and the other is under 3.00 MPa hydrogen pressure at 553 K. [Copyright &y& Elsevier]

• The current understanding of the fretting wear/corrosion response of materials for nuclear SG tube was reviewed. • The experimental programs and techniques used previously were described. • The effects of environmental and mechanical parameters on fretting wear were analyzed. • The microstructure evolution was summarized. Revealing the fretting failure law and mechanism of steam generator tubes is a critical issue to ensure the safe operation of nuclear power plants. This paper reviews the current understanding of the response of nuclear steam generator tube materials (Alloy 600, Alloy 690 and Alloy 800) to fretting wear, focusing on the effects of environment factors (temperature, pH and oxygen content), mechanical parameters (sliding amplitude, normal force and frequency) and materials state (grain size, carbide volume fraction, size and distribution, and surface treatment). Related characterization work has also been reviewed to discuss the fretting corrosion and failure mechanism of the materials. The future research direction that should be taken for the improvement of the understanding of the fretting wear of steam generator tubes has been suggested. [ABSTRACT FROM AUTHOR]

• The oxidation behavior of a 9Cr-4.5Al ODS steel in 600℃ supercritical water was investigated. • A thin alumina layer formed by pre-oxide treatment can well protect the sample at the beginning of the corrosion test. • The existence of M 23 C 6 (M = Cr, Fe) in the 9Cr-4.5Al ODS steel is detrimental to oxidation resistance. • All samples follow the "available space model" oxidation mechanism as exposure time is extended. The oxidation behavior of a 9Cr-4.5Al ODS steel in 600℃ supercritical water with 200 ppb dissolved oxygen was investigated with and without a pre-oxidation heat treatment. In general, results suggest that all samples follow the "available space model" oxidation mechanism as exposure time is extended. Based on the microstructural analysis, it is found that a thin alumina layer formed by pre-oxidation treatment is initially protective up to approximately 100 h. However, this passive film becomes ineffective due to the existence of M 23 C 6 (M = Cr, Fe) and the insufficient content of Al or/and Cr in the steel. [ABSTRACT FROM AUTHOR]

• The intergranular (IG) carbides were found to have detrimental effects on the cracking in cold worked Alloy 690. • Removing IG carbides by prior solution annealing could effectively decreases the cracking growth rate. • The detrimental effect of IG carbides is more significant in subcritical water than in supercritical water. • The detrimental effect of IG carbides has been well explained through high-resolution characterization. The effect of intergranular (IG) carbides on the cracking behavior of cold worked Alloy 690 was studied in both subcritical and supercritical water (SCW) environments. The crack growth rate (CGR) was lower when IG carbides were removed by prior solution annealed (SA) treatment, indicating a detrimental effect of IG carbides. The presence of IG carbides enhances the local strain accumulation at the grain boundary due to the lattice mismatch, thus promotes the crack tip strain rate and increases the CGR. The detrimental effect of IG carbides is more significant in subcritical water than in SCW, which can be attributed to the different controlling parameters of cracking between these two environments. The widely recognized beneficial effect of IG carbides on stress corrosion cracking in Alloy 600 is detrimental in cold worked Alloy 690, which might be related to the different degrees of grain boundary oxidation that contributed to IG cracking. [ABSTRACT FROM AUTHOR]

• The 14Cr ODS steel was prepared by replacing Y 2 O 3 with Y 2 Ti 2 O 7 nanoparticles. • Y 2 Ti 2 O 7 -ODS steel showed better corrosion resistance in SCW for 1500 h. • A bilayer structure was formed in the corrosion scale of ODS steels. • The finer Y 2 Ti 2 O 7 exhibited more effective hindrance impacts on diffusion of ions. • Adding Y 2 Ti 2 O 7 can inhibit the formation of coarse Y-Al-O particles. 14Cr-4.5Al ODS steels were prepared by adding Y 2 Ti 2 O 7 and Y 2 O 3 nanoparticles respectively. Bilayer-structure corrosion scales were formed while the Y 2 Ti 2 O 7 -ODS steel showed a lower mass gain of 108.1 mg/dm2 in SCW for 1500 h. Compared with Y 2 O 3 , Y 2 Ti 2 O 7 with finer size and higher number density exhibited more effective hindrance impacts on the diffusion of ions. Furthermore, adding Y 2 Ti 2 O 7 in the ODS steel can provide more zero valent Al to form alumina film through inhibiting the formation of coarse Y-Al-O particles. Our work demonstrates that substituting Y 2 O 3 with Y 2 Ti 2 O 7 is an effective route to improve the corrosion resistance of Al-adding ODS steels. [ABSTRACT FROM AUTHOR]

• δ-ferrite inhibited the crack growth by creating a highly branched crack tip. • Ti(CN) at the γ/δ boundary tends to inhibit oxidation and impede crack growth. • The δ-ferrite facilitates the formation of Cr-rich oxides at the γ/δ boundary. The stress corrosion cracking behavior of 321 stainless steel has been studied in high temperature water. Analytical electron microscopy was utilized to characterize the cracking process to better understand the δ-ferrite effect. Results showed that δ-ferrite inhibited the crack growth by changing the cracking direction along the γ/δ boundary and creating a highly branched crack path. δ-ferrite was also a source of Cr to facilitate the formation of protective Cr-rich oxides at the γ/δ boundaries. Ti(CN) particles in the γ/δ boundary tended to blunt the crack tip and inhibit further oxidation, and thus impeded the total crack growth. [ABSTRACT FROM AUTHOR]

The definition and mechanism of superfine comminution is introduced and the characteristics of equipments in common use for superfine comminution were outlined. The advantages of Chinese traditional medicine processed by superfine comminution are analyzed. The stress was laid on the present state and their advantages and disadvantages of the equipments used in the processing of Chinese traditional medicine. Vibration mill was pointed out to be the optimal equipment for the superfine comminution of Chinese traditional medicine.