The SCC propagation behavior in the HAZ of 316NG remains insufficiently characterized. This study systematically evaluates SCC growth in HAZ specimens under simulated PWR primary water conditions (325 degrees C, 1200 mg/L B, 2 mg/L Li, both hydrogenated [30 mL (STP)/kg H2] and oxygenated [0.5 ppm O2] environments) at constant K = 30 MPa & sdot;m1/2. Compact tension (CT) specimens that contained artificial cracks positioned 1 mm and 4 mm from the weld fusion line were employed to asses SCC growth in the HAZ, where the crack propagation region extended to a normalized distance of 0.41-0.45 from the inner wall surface. Surprisingly, the HAZ exhibited crack growth rates marginally lower than or essentially comparable to those of the parent metal in both oxygenated and hydrogenated water environments. This suggests that compressive residual stresses in the SCC propagation region may mitigate the crack growth acceleration typically induced by strain hardening (up to 20 % hardness increase relative to the parent metal). High-resolution transmission electron microscopy (HRTEM) analysis demonstrated nickel (Ni) enrichment at grain boundaries ahead of advancing crack tips, attributed to rapid iron (Fe) diffusion along grain boundaries toward the crack tip and selective oxidation of Fe and chromium (Cr) at the crack tip. The oxide film formed a distinct bilayer structure, with an outer Fe3O4 magnetite layer and an inner FeCr2O4 spinel layer.

The electrochemical hydrogen permeation method is reliable for evaluating the intrinsic hydrogen permeation resistance due to its room-temperature operation. However, the control of electrochemical parameters for hydrogen permeation testing has rarely been reported. In this study, we discussed the effects of anode background current, cathode current density, and cycle times on the electrochemical permeation behavior of CLF-1 RAFM steel. Results show that the anode background current below 1μA can ensure the accuracy of the permeation test. There exists a diffusion delay for the first permeation loop of CLF-1 steel because of the hydrogen trap effect, which can be eliminated by annealing the steel at temperature of 740 °C for 2h. For the second and third permeation loops of CLF-1 steel, a sample with a high cathode current density tends to have a high permeation signal because of corrosion. Plating a protective nickel film can reduce the corrosion impacts for the hydrogen permeation test. The effects of hydrogen traps and corrosion on the permeation behavior were discussed in detail. Our study provides a promising approach for hydrogen permeation testing and hydrogen trap detection at room temperature.

The corrosion behavior of a TA16 titanium alloy during exposure in simulated water environment of small modular reactor (SMR) at 320°C for up to 5000 h was investigated by employing dedicated microstructure characterization. The corrosion weight gain curve of the alloy is found to follow a parabolic law with an exponential parameter of n = 0.738. Oxide scales formed on the alloy surface generally show a two-layer structure composed of a relatively compact inner layer (dense oxide layer) and a discontinuous outer layer (microcrystallites). The dense oxide in the inner layer corresponds to anatase TiO2 while the surface microcrystallite layer is mainly comprised of ilmenite FeTiO3. The number and size of the microcrystallites in the outer layer gradually increase with the exposure time. Fe ions from the corroded loop pipe materials should have participated in forming the outer layer. The compact inner layer is thickened gradually with the test time with its thickness growth curve featured by l = 4.245t0.588, which could better reflect the corrosion behavior of the TA16 alloy.

In this study, two Al-Cr-Ti ternary alloy coatings (denoted as AlCr and AlCrTi0.5) were fabricated on a Ti-4Al-2V alloy substrate by using a pulsed laser cladding method. Specific microstructure characteristics of those coatings were thoroughly revealed by using various characterization methods, with their hardnesses and wear rates measured by a Vickers indenter and a tribological tester. The results reveal that both AlCr and AlCrTi0.5 coatings are comprised of a body-centered cubic phase (beta-Ti phase with average grain sizes of 12.6 +/- 9.1 mu m and 14.6 +/- 10.0 mu m, respectively), which is related to non-equilibrium solidification and sluggish diffusion of alloying el-ements during the laser processing. Heat-affected zones of both the laser-cladded specimens are mainly composed of submicron martensitic laths (alpha '-Ti). Average microhardness values of the AlCr and the AlCrTi0.5 coatings are measured to be 526 +/- 37 HV and 510 +/- 24 HV, respectively, approximately two times higher than the substrate (270 +/- 8 HV). Their wear rates are almost the same,-2.2 x 10-4 mm3 N-1 m- 1, only-1/3 of that of the substrate. Based on dedicated microstructure analyses, the greatly enhanced performance of the laser-cladded coatings could be attributed to joint strengthening from strong solid solution and lattice distortion, as well as Al/Cr-induced phase structure differences from the substrate.

Due to the advantages of high thermal conductivity, high heat storage density per unit volume and large specific surface area, metal-based microencapsulated phase change material (MEPCM) has a broad application prospect in the field of medium/high-temperature heat storage. However, the problems of thermal expansion and large supercooling seriously restrict its development and application. Our previous research work showed that “double-layer coating, sacrificial inner layer” method can successfully solve the thermal expansion problem of metal-based MEPCM. Based on this method, we aim to further investigate the supercooling suppression of metal-based MEPCM by loading nanoparticles into the core material skillfully when sacrificing the inner layer. Phase change properties of three kinds of MEPCM loaded with different nanoparticles (nano-BN, nano-diamond, and nano-Fe) with the same concentration were compared. It was found that the supercooling suppression effect of nano-Fe was the best. Furthermore, supercooling suppression effect of nano-Fe with different concentrations was compared. The results demonstrated that nano-Fe with a concentration of 0.9% showed the best supercooling suppression effect. In addition, supercooling suppression effect of different particle sizes was compared. The results showed that the supercooling degree of MEPCM decreased by 41.5% and 5.6% when nano-Fe with a particle size of 50 nm and 100 nm was loaded, respectively, indicating that nano-Fe with the particle size of 50 nm is more effective than that of 100 nm. Finally, supercooling suppression effect of different coating methods was compared. The results showed that the supercooling suppression effect of “double-layer coating, sacrificial inner-layer” is much better than that of single-layer coating.

The high-cycle fatigue (HCF) experiments of 6XN stainless steel and alloy 825 were conducted under bending and rotating loads at room temperature (RT) as well as at 550°C in air. The results indicate that the fatigue limited stress of 6XN at RT is higher than that of 825, which consistent with the order of their tensile strength. The oxidation rate of the specimen increased at 550°C, therefore the fatigue life of the specimen decreased, among them 6XN was more sensitive to high temperature with the larger decreasing tendency which make the fatigue limited stresses of the two alloys more closer at 550°C. While 825 is more sensitive to the stress cycles, both materials have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula. The fracture morphology presents the areas of crack initiation, crack growth and fracture, and the fracture area has much dimples.

The fatigue experiments of commerce stainless steels including 347,316Ti and 310 were conducted under bending and rotating loadings.The environments were at room temperature(RT) as well as at 550℃ in air.The fracture morphology was observed by SEM,and the S-N curves were processed according to the experimental data.The results indicate the fatigue limited stresses for the 3 stainless steels were in the order of 347316Ti310,which consistent with the order of their tensile strength.Elevated temperature would accelerate the oxidation and therefore the fatigue life would decrease,among them 347 was more sensitive to temperature with the maximum decreasing tendency.All the 3 stainless steels have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula.The fracture morphology presents areas of crack initiation,crack growth and fracture,the width of fatigue ripples is about 1μm,the fracture area has much dimples,and 347 presents much cavities of different sizes in dimples.