This study unveils the atomic-scale mechanism underlying the enhanced oxidation resistance of silicon (Si)-alloyed ferritic/martensitic (F/M) steels in oxygen-saturated liquid lead-bismuth eutectic (LBE) at 600 degrees C. Microstructure characterization reveals that Si preferentially segregates to the inner oxide layer and internal oxidation zone (IOZ). At 1.2 wt.% Si, the inner oxide forms a continuous network of hierarchical "core-shell" structures. Si-depleted magnetite (Fe3 O4 ) constitutes the "cores", while the "shells" exhibit a sandwich-like architecture composed of Fe-Cr spinel and amorphous silica bands. These sandwichlike "shells" serve as critical diffusion barriers and originate from "CrO2 -SiO2 -CrO2 " plate-like nano-oxides at the oxidation front. Inward-diffusing oxygen atoms first occupy the interstitial sites in the Fe lattice, attracting neighboring Cr atoms, followed by phase transformation into CrO2 , coherently bonding with the Fe(100) surface. This configuration further evolves into a sandwich-like structure with a similar to 1 nm thick amorphous silica situated between two CrO2 nanolayers. This atomic/nanoscale oxide formation sequence is considered a precursor stage for the observed "shell" structures, yet it deviates from the more stable oxide phases (e.g., Cr2 O3 and silica) predicted by bulk thermodynamics. Density functional theory (DFT) calculations of various oxide-steel interfaces confirm that the CrO2 -Fe coherent interface possesses the highest stability, suggesting that the oxide nucleation at the atomic/nanoscale is governed by minimization of interfacial energy rather than bulk thermodynamics. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The liquid metal embrittlement (LME) behavior of a Si-alloyed 12Cr ferritic/martensitic (F/M) steel (0.6 wt.% Si) in lead-bismuth eutectic (LBE) was investigated via slow-strain-rate tensile tests at 250-550°C and dissolved oxygen concentrations of 10-9-10-5 wt.%. The steel exhibits a distinct ductility trough under moderate-oxygen (10-8-10-7 wt.%) at 250-450°C, with maximum embrittlement at 350°C. This temperature window is independent of Si content (0-1.09 wt.%). At 350°C, high oxygen (10-6-10-5 wt.%) suppresses LME via a protective oxide layer, while moderate and low oxygen (10-9-10-7 wt.%) cause severe embrittlement (embrittled area fractions of 96 % and 91 %, respectively), with no significant difference between the two, revealing a threshold effect. A comparison with literature further shows that Si content does not shift the temperature window, but strongly affects fracture toughness degradation (nearly 71 %) versus a modest effect on elongation reduction (18-42 %), indicating that Si influences crack propagation more significantly than crack initiation. These findings provide new insights into the coupled roles of temperature, oxygen, and Si in LME, with implications for oxygen control strategies in LBE-cooled reactors.

The influence of thermal aging on the corrosion behavior of type Z3CN20-09 M cast austenitic stainless steel (CASS) was systematically investigated in simulated pressurized water reactor (PWR) primary water (325 degrees C, 2 ppm Li, 500 ppm B). Thermal aging of ferrite markedly accelerated corrosion in a phase-dependent manner, with austenite showing higher susceptibility to oxidation than ferrite. Upon pronounced spinodal decomposition of ferrite (e.g., at 400 degrees C/16000 h or 450 degrees C/6000 h), the maximum increase in inner oxide thickness was suggested to be a factor of similar to 1.51 on austenite versus only similar to 0.83 on ferrite, albeit with limited data. At the oxide/ferrite interface of the specimen aged at 450 degrees C/6000 h, alternating FeCr2O4 and Cr2O3 zones were observed, which directly correlated with Cr-rich and Fe-rich fluctuations arising from spinodal decomposition. Notably, the FeCr2O4 regions appeared to undergo faster matrix oxidation, while the Cr2O3 regions exhibited slower oxidation. Thermal aging appears to alter the original micro-galvanic environment and introduce new couplings via ferrite decomposition, such as between austenite and Cr-enriched alpha ' phase or G phase and among the decomposed phases, which may account for the accelerated oxide growth.

This study investigates the distinct corrosion behavior of 12 wt% Cr F/M steels in LBE at 550 degrees C, with a focus on the influence of the initial matrix microstructure. Two steels of same composition but different initial microstructures were examined, one predominantly martensitic and the other predominantly ferritic. Under high-oxygen conditions (HOC, 1.01 x10(-3) wt% to 1.84 x10(-3) wt%), both steels formed duplex oxide scales of similar total thickness. However, the predominantly ferritic steel exhibited a thinner and discontinuous IOZ. In contrast, under low-oxygen conditions (LOC, 1.82 x10(-13) wt% to 6.25 x10(-8) wt%), the predominantly ferritic steel underwent deep LBE penetration (maximum similar to 40 mu m after 5000 h), markedly greater than that observed in the predominantly martensitic steel (maximum similar to 10 mu m after 5000 h). The key mechanistic insight reveals that the high density of microstructural interfaces (e.g., martensitic lath boundaries) within the martensite provides abundant pathways for rapid elemental diffusion (e.g., O and Cr), thereby promoting the nucleation and growth of the IOZ. Furthermore, the abundant Cr-rich M23C6 carbides precipitated at these microstructural interfaces accelerate the oxidation of interfaces due to the lower oxidation free energy of Cr. The resulting oxides facilitate the rapid formation of a continuous scale composed of Fe-Cr spinel and Cr2O3. Importantly, this oxide layer acts as an effective barrier against dissolution and LBE attack under low-oxygen conditions. This work demonstrates the detrimental effect of ferrite on the corrosion resistance of 12 wt% Cr F/M steels in LBE and underlines the importance of microstructural design to maximize martensite content for enhanced performance.

This study demonstrated that the optimized AlTiFeCrMoSi0.2 high-entropy alloy (HEA) coating can significantly improve the corrosion resistance of the T91 steel in high-temperature liquid lead-bismuth eutectic (LBE) environment. Compared with the commercial T91 steel, the thickness of oxide scale on the HEA-coated steel after 1000 h of corrosion in oxygen-saturated and low-oxygen LBE environment was reduced by factors of 5.7 and 13.11, respectively. Under saturated oxygen conditions, the oxide scale on T91 steel was dominated by Fe3O4 and FeCr2O4 spinel phases. In contrast, the coating system developed additional protective layers of TiO2 and continuous Al2O3.Under low oxygen environments, the oxide structure on T91 steel transitioned to a mixture of Cr2O3 and FeCr2O4, while the coating consistently formed TiO2 and continuous Al2O3 layers. The oxide layer of the coating effectively prevented the penetration of lead and bismuth, thereby suppressing the occurrence of localized dissolution corrosion. Theoretical calculations confirmed the critical roles of TiO2 and Al2O3 in enhancing the coating's resistance to liquid LBE corrosion. This study provides new insights into the development of LBE-corrosion-resistant approaches.

The long-term integrity of structural materials in lead-cooled fast reactors is challenged by coupled irradiation and corrosion. Here, SIMP ferritic/martensitic steel was subjected to 3.5 MeV Fe-ion irradiation (peak dose of 50 dpa) and oxidation at 650 degrees C for 72 h in high vacuum with trace oxygen. Compared with the pre-oxidized reference (oxygen-saturated LBE at 500 degrees C for 500 h), irradiation enhances internal oxidation and produces a continuous SiO2 layer at the oxide/substrate interface. The internal oxidation zone contains elongated Cr2O3 particles aligned with the ion-beam direction and surrounded by amorphous SiO2, accompanied by a Cr-depleted region near the oxidation front. A vacancy-assisted, defect-directed pathway is proposed to explain the microstructural evolution of the IOZ under coupled irradiation-oxidation conditions.

The corrosion fatigue crack growth (CFCG) behavior of a Zr-Sn-Nb alloy was systematically investigated in simulated PWR primary water (320 degrees C, 12.5 MPa) under controlled dissolved oxygen (DO: 10-500 ppb) and dissolved hydrogen (DH: 0-30 cc (STP)/kg H2O) conditions. A pronounced environmental acceleration is demonstrated, with the CFCG rate under low frequency (0.001 Hz), high stress ratio (0.9), and 100 ppb DO exceeding the air value by up to a factor of 250. In contrast, DO and DH variations exhibit only a modest influence on crack growth kinetics within the tested ranges. Microstructural analyses reveal a crack-tip oxide scale predominantly composed of monoclinic ZrO2, accompanied by limited dislocation activity and extensive needleshaped hydride precipitation in the adjacent matrix. The observed behavior is consistent with a slip-oxidationrupture mechanism, which is established as the governing process. These findings underscore that mechanical driving forces (frequency, stress ratio), rather than bulk water redox chemistry, dominate the CFCG response of zirconium alloys in this environment.

Corrosion fatigue crack growth (CFCG) of thermally aged Z3CN20-09M cast austenitic stainless steel (CASS) was studied in simulated pressurized water reactor (PWR) primary water. Specimens were aged at 400 degrees C (6,000 h and 16,000 h) and 450 degrees C (6,000 h) and tested under varied loading conditions. The PWR primary water increased crack growth rates by typically up to 15 times compared to air, due to synergy between cyclic loading, corrosion, and the duplex microstructure, yet with weaker frequency and stress intensity dependence than conventional austenitic steels. Thermal aging had a limited influence (acceleration factor < 4), indicating that ferrite decomposition does not substantially affect the crack-tip oxide film (inner spinel/outer magnetite bilayer) or its rupture behavior. The study further establishes that all measured corrosion fatigue crack growth rates consistently fall below the ASME Code Case N-809 design curve, validating its continued applicability as a conservative safety benchmark for aged CASS components in PWR environments.

The corrosion fatigue crack growth (CFCG) behavior of a Zr–Sn–Nb alloy was systematically investigated in simulated PWR primary water (320 °C, 12.5 MPa) under controlled dissolved oxygen (DO: 10–500 ppb) and dissolved hydrogen (DH: 0–30 cc (STP)/kg H₂O) conditions. A pronounced environmental acceleration is demonstrated, with the CFCG rate under low frequency (0.001 Hz), high stress ratio (0.9), and 100 ppb DO exceeding the air value by up to a factor of 250. In contrast, DO and DH variations exhibit only a modest influence on crack growth kinetics within the tested ranges. Microstructural analyses reveal a crack-tip oxide scale predominantly composed of monoclinic ZrO₂, accompanied by limited dislocation activity and extensive needle-shaped hydride precipitation in the adjacent matrix. The observed behavior is consistent with a slip-oxidation-rupture mechanism, which is established as the governing process. These findings underscore that mechanical driving forces (frequency, stress ratio), rather than bulk water redox chemistry, dominate the CFCG response of zirconium alloys in this environment.

The stress corrosion cracking (SCC) resistance of a Z3CN20-09 M duplex stainless steel (DSS) was systematically studied and compared to conventional single-phase austenitic stainless steel (316NG) under simulated pressurized water reactor (PWR) primary water conditions. Results show that the DSS exhibits much lower SCC growth rates than the 316NG in either deformed or high corrosion potential conditions. High-resolution microstructural characterization revealed the oxidation and crack-tip behaviors during SCC tests in simulated primary water, while in-situ SEM tensile experiments elucidated the deformation compatibility between austenite and ferrite phases, confirming that the duplex structure fundamentally enhances SCC resistance. The ferrite phase, which contains higher Cr, appears to promote the formation of protective chromium-rich oxide layers, thereby reducing oxidation-driven crack propagation. Additionally, ferrite shows lower strain accumulation and appears to limit crack propagation at austenite-ferrite interfaces.

Tensile fracture behavior of a Co-free Al0.3CrFeNi high-entropy alloy (HEA) in air and liquid lead-bismuth eutectic (LBE) was investigated to reveal its liquid metal embrittlement (LME) susceptibility and the underlying cracking mechanisms. The as-forged alloy exhibited a multiphase microstructure with dominant FCCaustenitic matrix, Cr-rich BCC-ferrite and dispersed B2-NiAl nanoparticles. In air at 350 degrees C and 500 degrees C, the alloy showed excellent ductility, with surface cracks observed to preferentially propagate along FCC/BCC interphase boundaries (IBs) and involve extensive plastic deformation and evident crack blunting. In contrast, severe LME occurred in LBE, particularly at 350 degrees C, where the total elongation to failure (TE) deceased by > 90% compared to air. Multiscale characterization showed phase- and temperature-dependent LME behavior of this HEA in LBE. At 350 degrees C, cracks propagated transgranularly through BCC-ferrite and B2-NiAl phases, while FCCaustenite exhibited mixed transgranular and intergranular cracking with intense dislocation activity retarding crack propagation. Cracks also propagated along FCC/BCC IBs, mainly driven by the deformation incompatibility between these two phases. Moreover, an elliptical LBE droplet was observed at the FCC/BCC interface, with a measured contact angle of similar to 120 degrees, indicating partial wetting of LBE at this type of interface. At 500 degrees C, evident crack-tip blunting observed due to improved dislocation mobility and more activated slip systems. The dominant failure mode shifted to interfacial decohesion of FCC/BCC IBs, suggesting the occurrence of an interfacial wetting transition, which was assisted by tensile stress. Given its strong susceptibility to LME, this alloy is not recommended for load-bearing purposes in LBE.

The predeformed 316NG (00Cr17Ni12Mo2N) was prepared by cold rolling at room temperature and hot rolling at 400 degrees C. The effect of predeformation on fatigue crack growth both in 325 degrees C deaerated water and room temperature air was investigated. The effect of predeformation on corrosion fatigue crack growth (CFCG) in 325 degrees C deaerated water was much smaller than that on fatigue crack growth. The cold rolling significantly enhanced CFCG rates while the applied Delta K closed to 11 MPapm or the applied loading frequency decreased to 0.1 Hz. The accelerating effect of hot rolling on CFCG tended to become evident until the predeformation increased to 30%. Dynamic recovery was observed near the corrosion fatigue crack tip in hot-rolled 316NG, which may result in relatively low CFCG rates.

Corrosion resistance of AlCrFeTi and AlCrFeTiY coatings were evaluated in static and flowing lead bismuth with oxygen-controlled precondition at 550 degrees C, both the oxygen concentration of static and flowing liquid lead bismuth was 1 x 10(-5) wt%. Double-layered compact oxide layers were formed on the surface of AlCrFeTi coating which consist of outer Fe/Cr oxide layer and inner Al/Ti oxide layer after exposure in static liquid lead bismuth for 2000 h, while uneven Fe/Cr oxide layers formed on AlCrFeTiY coating and the oxygen content significantly increase inside the coating, indicating the weaker antioxidant properties of AlCrFeTiY. Besides, structural integrity of AlCrFeTi was well preserved after erosion test in flowing lead bismuth (similar to 2 m/s) for 1000 h, localized bulges existed in eroded AlCrFeTiY coating. Magnetron sputtering method was utilized for coating preparation and the in-depth corrosion mechanism of AlCrFeTi and AlCrFeTiY coating was discussed.

Siliconized layer was prepared on SUS403 stainless steel using molten salt method. The microstructure, wear and electrochemical properties of the siliconized layer were investigated. The results show that the growth activation energy of the siliconized layer is approximately 93.5 kJ/mol. The siliconized layer exhibits spinel-like grains, while the cross-sectional morphology displays a columnar structure. The siliconized layer is mainly composed of Fe3Si and Fe2Si. The microhardness and wear resistance of the siliconized layer has increased by 87

This paper investigates the microstructure, mechanical properties, and abrasive wear behavior of low alloy martensitic steel subjected to four different heat treatment conditions: quenching at 850 degrees C and 925 degrees C followed by tempering at 150 degrees C, and quenching at 850 degrees C followed by tempering at 200 degrees C and 350 degrees C. The primary focus is on the relationship between the martensitic variants and abrasive wear resistance, and the wear mechanisms of the specimens are systematically analyzed. The results demonstrate that the martensitic variants in all samples undergo notable changes under the four heat treatment conditions. As the quenching temperature increases, the prior austenite grain size increases and grain uniformity deteriorates, leading to a shift in variant selection within the close-packed plane (CP) groups of martensitic -from being dominated by CP1 and CP2 to being dominated by CP2 and CP4. With increasing tempering temperature, the distribution of the 24 martensitic variants tends to become more uniform. Both effects negatively impact wear resistance. The wear mechanism appears to be dominated by surface fatigue wear, accompanied by micro-cutting. Variants of CP1 and CP2 contribute most significantly to wear resistance, with CP1 having a more pronounced effect than CP2.

The microstructure evolution and embrittlement of Z3CN20-09 M CASS were investigated by thermal aging up to 30,000 h at 325 degrees C, 400 degrees C and 450 degrees C. The results show thermal aging was dominated by the nucleation of G phases, formation of alpha and alpha' phases by spinodal decomposition of ferrite rather than by the growth. The spinodal decomposition of ferrite phase and G phase precipitation tends to be initiated at about 13 equivalent service year, resulting in a sharp drop of about 220 J in impact energy. After an equivalent service time of 35 years, the microstructure and impact energy remain fundamentally stable, and the impact energy at room temperature is still above 100 J. The impact fractography reveals two major embrittlement modes: delta ferrite embrittlement and gamma/delta phase boundary embrittlement.

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.

This study used 347H heat-resistant steel as the base material and systematically investigated the microstructural evolution and second-phase precipitation in typical regions during welding and aging processes. The results showed that the weld metal consisted of austenitic dendrites and inter-dendritic ferrite in a lath-like form. In the welded samples, the HAZ (Heat-Affected Zone) and BM (Base Material) regions were composed of equiaxed crystals. The microhardness of the HAZ was lower, mainly due to the coarser grain size and fewer second-phase particles. After aging at 700 °C, the hardness of all regions of the welded joint increased significantly due to the precipitation of M23C6 and MX phases. When the aging temperature increased to above 800 °C, the stability of the M23C6 phase decreased, and the diffusion rate of Nb in the matrix accelerated, promoting the preferential growth and stable presence of the MX phase. As the MX phase competes with the M23C6 phase for carbon during its formation, its generation suppresses the further precipitation of the M23C6 phase. Under 800 °C aging conditions, the γ/δ interface exhibited high interfacial energy, and the Nb content in the ferrite was higher, which facilitated the formation of the MX phase along this interface. As the aging temperature continued to rise, the hardness of the HAZ and BM regions initially increased and then decreased. After aging at 800 °C, the hardness decreased because the M23C6 phase no longer precipitated. After aging at 900 °C, the hardness of the HAZ and BM regions significantly increased, mainly due to the large precipitation of the MX phase. The hardness of the W (Weld Zone) and FZ (Fusion Zone) regions gradually decreased with the increase in aging temperature, mainly due to the reduction of inter-dendritic ferrite content, coarsening of second-phase particles, weakening of the pinning effect, and grain growth. In the 900 °C aging samples, the MX phase particle size from largest to smallest was as follows: W > HAZ > BM. The Nb-enriched ferrite provided the chemical driving force for the precipitation of the MX phase, while the δ/γ interface provided favorable conditions for its nucleation and growth; thus, the MX phase particles were the largest in the W region. The HAZ region, due to residual stress and smaller grain boundary area, had MX phase particle size second only to the W region.

In this study, the solidification behavior of 310S stainless steel was systematically investigated by combining high-temperature confocal laser scanning microscopy (HT-CLSM), microstructural characterization, and thermodynamic calculations. The focus was on the formation and transformation of ferrite, secondary-phase precipitation, and elemental segregation behavior, with comparisons made with 304 stainless steel. The effects of an Al addition and cooling rate were also explored. The results show that the solidification sequence of 310S stainless steel is L → L + γ → L + γ + δ → δ + γ, in which austenite nucleates early and grows rapidly, followed by the precipitation of a small amount of δ-ferrite in the later stages of solidification. In contrast, 304 stainless steel solidifies according to L → L + δ → L + δ + γ → δ + γ, with a rapid δ → γ transformation occurring after solidification. Compared with 304, 310S stainless steel exhibits a reduced ferrite fraction and a significantly increased σ phase content. The σ phase primarily precipitates directly from δ-ferrite (δ → σ), while M23C6 preferentially forms at grain boundaries and δ/γ interfaces, where δ-ferrite not only provides fast diffusion pathways for Cr but also nucleation sites. The solidification segregation sequence in 310S stainless steel is Cr > Ni > Fe, with Cr and Ni showing positive segregation and Fe showing negative segregation. The addition of Al does not alter the solidification mode of 310S stainless steel but refines austenite grains, reduces interdendritic solute enrichment, decreases segregation, lowers both the size and fraction of ferrite, and suppresses the precipitation of σ and M23C6 phases. This effect is mainly attributed to the reduction of δ/γ interfaces, which weakens the preferred nucleation sites for M23C6. Increasing the cooling rate enhances non-equilibrium solute segregation, promotes ferrite formation, inhibits the δ → γ transformation, and ultimately retains more ferrite; the intensified segregation further accelerates the δ → σ transformation.

9 wt. % Cr F/M steels with Si content of 0 wt. %, 0.4 wt. %, 0.7 wt. % and 1.0 wt. % were prepared and tested in oxygen-saturated static and flowing LBE at 550 degrees C for 2000 h. Results show that Si doping facilitated the formation of the early-stage oxide film, extended the incubation period for accelerated oxidation (up to 1500 h similar to 2000 h for 1.0 wt. % specimen in static LBE) and reduced the growth rate of oxide films. Si is found distributed in the form of a nano-scale Si-enriched oxide layer at the oxide film/substrate interface and martensite lath interfaces, acting as a reticular diffusion barrier, mitigating the oxide film growth rate. Although flowing LBE (1.85 m/s) significantly weakens these effects, but overall, Si-containing F/M steels exhibit enhanced oxidation resistance compared to Si-free counterparts.