Superalloys are used widely in national defense, energy, maritime, aviation, and other vital areas requiring stable and reliable materials owing to their excellent oxidation and heat corrosion resistance, high-temperature strength, good fatigue performance, and fracture toughness. The presence of a coherent gamma prime (γ') precipitate is the main factor affecting the high-temperature mechanical properties. Therefore, obtaining the quantitative and statistical γ' precipitate data is indispensable for examining and developing new superalloys. On the other hand, conventional instruments and methods barely achieve this goal. In this study, high-throughput field emission scanning electron microscope (high-throughput SEM) was introduced because of its high-speed imaging and original position visualization. Based on the high-throughput SEM, an innovative deformation GH4096 superalloy prepared at five different solution cooling rates were used as an object to establish a quantitative and statistical method for characterizing the primary, secondary, and tertiary γ' precipitates. Many images of γ' precipitates with magnifications of ×57000 and ×3000 were obtained rapidly, and methodologies for recognizing the γ' precipitates were developed using MIPAR software. Matrices of images of different amounts were formed. Through these methodologies, information on these matrices was obtained, including the ratio of the primary γ' precipitates area fractions between images with magnifications of ×57000 and ×3000. The ratio between the amounts of secondary and tertiary γ' precipitates and the area fraction of the secondary and tertiary γ' precipitates varied with the number of images investigated, respectively. By comparing the tendencies of these three results, the minimum field of view that could represent the actual distribution of γ' precipitates was set to a matrix of 13 × 13 images with a magnification of ×57000 and a pixels square of 2048 × 2048. Considering the consistency between the results of the standardized small-angle X-ray scattering (SAXS) and γ' precipitates in the 13 × 13 images, the established method was quantitative in characterizing the primary, secondary, and tertiary γ' precipitates of GH4096 superalloy. The results of the samples with five different solution cooling rates showed that the solution cooling rates strongly influenced the morphology and quantitative results of the γ' precipitates. Moreover, the behavior of the precipitates corresponded to the classical nucleation growth mechanism and Ostwald Ripening. The solution cooling rates influenced the tensile strength of the samples. The samples exhibited excellent tensile strengths at relatively faster cooling rates, more secondary γ' precipitates, and a higher total area fraction of secondary and tertiary γ' precipitates. Overall, a GH4096 superalloy was prepared using the established method. The statistical and quantitative results of the γ' precipitates highlight a novel way of studying the impact of the solution cooling process on γ' precipitates that can predict the performance of GH4096 superalloys.

GH4096 alloy were used for disks and shafts of advanced gas turbine engines owing to its excellent properties such as resistance to creep, fatigue, and corrosion as well as microstructure stability up to about 700^oC. In this study, GH4096, a hard-to-deform disk superalloy, was processed through an advanced cast and wrought route to avoid the expensive power metallurgy (P/M) route. Many types of full-scale disk forgings possessing homogeneous fine-grained microstructures were successfully carried out, and the ultrasonic inspectability was comparative to that of the alloy produced by the P/M route. The effects of the initial grain size and strengthening phase on hot deformation behavior and dynamic recrystallization (DRX) were studied by OM, SEM, EBSD, and TEM under different deformation parameters. The results showed that as the initial grain size decreased within the temperature range of 1050-1120^oC, the flow peak stresses decreased and the fractions of DRX increased. With an increase in the initial grain size, the thermal deformation temperature required for complete dynamic recrystallization decreased, and also the critical strain of dynamic recrystallization decreased. The initial grain size and the strain did not affect the recrystallized grain size when deformed at a sub-solvus temperature. The thermal deformation constitutive equations related to the initial grain sizes were established and the activation energies of thermal deformation related to the original grain sizes were calculated. The effect of γ' phase size on the thermal deformation behavior in as-cast microstructure was studied. In the sub-solvus temperature range, the thermal deformation resistance could be effectively reduced with the increase in the size of γ' phase, the critical strain of DRX was decreased, and the DRX fraction was also increased. The dynamic recrystallization mechanisms related to the γ' phase and initial grain size were also discussed. DRX nucleation takes place at the sub-grains near original grain boundaries for samples with larger initial grain size deformed at sub-solvus temperature. For samples with fine initial grain size, the interface slip of incoherent γ' phase is the significant dynamic softening mechanism during the sub-solvus temperature deformation. For as-cast samples, the main dynamic softening mechanism is original grain boundary bowing out DRX nucleation and coarse second-phase-induced DRX nucleation.

Under complex cyclic force/thermal multifield coupled service conditions, one of the most common failure types of aeroengine turbine disks is thermo-mechanical fatigue (TMF) failure. In metallurgy, petrochemicals, nuclear energy, aviation, and other industries, the GH4169 superalloy is frequently used. To further enrich the fatigue performance data of this alloy, in-phase (IP) and out-of-phase (OP) TMF tests were conducted on the nickel-based superalloy GH4169 at 0.6% and 0.8% strain amplitudes with temperature cycling from 350^oC to 650^oC. The TMF hysteresis loops, cyclic stress response behavior, fatigue crack initiation, propagation behavior, and fatigue life were analyzed. The experimental results show that the TMF stress-strain curves show tensile-compression stress asymmetry, and there is obvious cyclic softening in the high-temperature half-cycle. The TMF life is shorter than the isothermal fatigue life at the peak temperature under the same strain amplitude. Moreover, the increase of strain amplitude leads to the increase of cyclic deformation and reduces the fatigue life. The fracture analysis and the results show that the OP TMF cracks display transgranular fracture, while the IP TMF cracks show intergranular fracture. Finally, the TMF cyclic deformation behavior was simulated using the Chaboche viscoplastic model, and the simulation results were consistent with the experimental results, reflecting the basic characteristics of TMF.

The Zhanjiang oil station is located near the sea, and corrosion factors such as Cl^-, SO₂, humidity, and UV irradiation in the surrounding environment will endanger the service life of the common materials. Carbon steel Q235 is commonly used as an oil tank pressure ring, pipeline steel L415 is used for oil and gas transportation, and pressure vessel steel 16MnNi is commonly used as the outer wall material of an oil tank. These materials are easily corroded when they are directly exposed to the atmosphere, but there have been few studies in recent years on the short-term corrosion behaviour of common metal materials in oil stations in high humidity and high irradiation industrial marine atmosphere environments. In this work, the initial corrosion behaviour of carbon steel Q235, pipeline steel L415, and pressure vessel steel 16MnNi exposed to the real Zhanjiang atmospheric environment for 180 d were studied through weight loss analysis, corrosion product analysis, corrosion morphology observation, and electrochemical analysis. According to the thickness loss data, carbon steel Q235 had the weakest corrosion resistance of the three materials, whereas pipeline steel L415 had the best corrosion resistance. These common materials were exposed to the same atmospheric environment for the same amount of time, resulting in the same corrosion products in the rust layer, which contained α-FeOOH, γ-FeOOH, and Fe₃O₄. The difference was that the rust layer of carbon steel Q235 contained a high concentration of β-FeOOH, which may have facilitated the corrosion process. The concentration of γ-FeOOH and Fe₃O₄ varied amongst the three materials. The rust layer of carbon steel Q235 contained more γ-FeOOH and Fe₃O₄, followed by pressure vessel steel 16MnNi and pipeline steel L415, which had the least γ-FeOOH and Fe₃O₄. Furthermore, carbon steel Q235 had the thinnest rust layer and the greatest thickness loss, whereas pipeline steel L415 and pressure vessel steel 16MnNi had a thicker rust layer and less thickness loss. The results of electrochemical experiments showed that the rust layer of carbon steel Q235 has the weakest ability to protect the matrix, whereas the rust layer of L415 has the best ability to protect the matrix. Additionally, the synergistic effect of Cl^-, SO₂, and UV irradiation destroyed the protective layer of the rust layer and accelerated the corrosion.

Marine carbon steels are constantly subjected to active corrosion due to significant amounts of aggressive agents in seawater. Once sand particles are entrained in seawater, the relative movement between the seawater and marine structures could further lead to erosion-corrosion of marine carbon steels. The size of the sand particles would play an important role in the synergy of erosion and corrosion. In this work, the erosion-corrosion performances of the EH36 marine carbon steel at sand impacts of different particle sizes were studied in 3.5%NaCl solution using the EIS, gravimetric measurements, and surface morphology characterization. A computational fluid dynamics simulation is used to simulate the impact velocity and trajectory of the sand particles in the test cell. The simulation results reveal that at a relatively lower flow velocity of 2 m/s, the average impact velocity of the sand particles on the electrode surface is presented as a decreasing trend along with increasing size (100-850 μm). However, increment in the particle size could still lead to rise in the impact energy due to mass increase. The EIS and gravimetric measurement results show that at low flow rate conditions, corrosion is the main contributor to the steel degradation in the sand-containing electrolyte. Meanwhile, corrosion is the prerequisite for severe erosion in this case. The steel loss induced by erosion would rise with an increase in the particle size. The surface characterization results show that the erosion-corrosion pattern changed from the typical “flow mark” to pitting damage with increasing particle size. It suggests that the increase in the impact energy could lead to a pitting initiation, thereby accelerating localized corrosion. It was determined that the particle size increase would promote the synergy of erosion and corrosion compared to pure corrosion, pure erosion, and erosion-corrosion performances. The initiation and propagation of localized erosion-corrosion are determined by the coupled effect of local sand impacts, anodic dissolution, and flow-enhanced analyte transportation. When the diameter of the sand particle is 100 μm, the erosion-corrosion process is controlled by the analyte transportation, leading to the formation of a typical “flow mark”. When the diameter of the sand particle ranges from 430 μm to 850 μm, the synergy of the sand impact and local anodic dissolution would effectively retard the analyte transportation, resulting in the formation of stable pitting damage.

High-Mn austenitic Fe-Mn-C twinning-induced plasticity (TWIP) steels are prospective candidates in many industrial fields, owing to their excellent mechanical properties. However, these steels show poor corrosion resistance, which affects their performance and prevents their applications particularly in aqueous environment. In this study, an effective way to improve the corrosion resistant property of TWIP steels was described by understanding the corrosion behavior of TWIP steel that was alloyed with Cr. A series of Fe-25Mn-xCr-0.3C (x = 0, 3, 6, 9, and 12, mass fraction, %) TWIP steels were prepared in a vacuum arc melting furnace using high purity raw materials (≥ 99.8%). Thereafter, the resulting steels were solution treated at 1200^oC for 2 h under an argon atmosphere. The effect of Cr addition on the corrosion behavior of the prepared TWIP steels was investigated using various analytical techniques including XRD, potentiodynamic polarization, electrochemical impedance spectroscopy, and XPS. XRD results showed that the TWIP steels with Cr content that ranged from 3% to 12% retained their single austenite phase. Moreover, increasing the concentration of Cr in the alloys substantially increased and decreased the corrosion potential and corrosion current density, respectively. These resulted in an improvement in the corrosion resistant property of the alloys, which was verified by the increase in the charge transfer resistance found in the Nyquist plots. Meanwhile, XPS results revealed that the prepared quasi-passive oxide film was composed of FeO, Fe₂O₃, FeOOH, MnO, MnO₂, Cr₂O₃, and Cr(OH)₃. Furthermore, these results showed the progressive enrichment of Cr oxides and decrease of both Fe and Mn oxides in the outermost oxide as the Cr content was increased. The improved corrosion resistance of the prepared TWIP steels was caused by the protective Cr oxide film.

An increased temperature causes the breakaway oxidation of zirconium alloys and the loss of structural integrity under the loss of coolant accident (LOCA). Thus, to enhance the inherent safety of nuclear reactors, the idea of developing accident-tolerant fuel (ATF) is proposed. One of the promising candidate materials for ATF cladding is FeCrAl alloy. The theoretical basis and guidance for FeCrAl alloy's composition optimization can be obtained by investigating the effects of alloying elements on the oxidation behavior and mechanism. Thus, the effect of Y on the oxidation behavior of Fe22Cr5Al3Mo alloy in 1000 and 1200^oC high-temperature steam was investigated in this study. Two types of Fe22Cr5Al3Mo-xY (x = 0, 0.15, mass fraction, %) alloys, denoted as 0Y and 0.15Y, respectively, were fabricated and oxidized in 1000 and 1200^oC high-temperature steam for 2 h, employing a simultaneous thermal analyzer. The microstructure, crystal structure, and composition of the samples before and after oxidation were analyzed using XRD, FIB, EDS, and TEM. The findings indicate that adding 0.15%Y increases the weight gain rate of FeCrAl alloy in 1000^oC high-temperature steam, but decreases the weight gain rate of FeCrAl alloy in 1200^oC high-temperature steam. Furthermore, adding 0.15%Y can inhibite the formation of ridge morphology on the surface of oxide film and improve the thickness uniformity and interface flatness of oxide film. The oxide films formed on the 0Y and 0.15Y alloys are both α-Al₂O₃ under the condition of 1000 and 1200^oC high-temperature steam for 2 h. In the Al₂O₃ oxide film, there is hcp-(Cr, Fe)₂O₃ paralleled to the oxide/metal (O/M) interface. AlYO₃, Y₂O₃, and Fe(Cr, Al)₂O₄ are present in the Y-rich oxides growing toward the matrix in 0.15Y alloy oxidized in 1200^oC steam. The effect of Y on the oxidation behavior of FeCrAl alloy at various temperatures was discussed from the viewpoint of the influence of Y on the microstructure evolution of oxide film.

The South China Sea is a marine atmosphere environment with high humidity, high salt content, and strong radiation. Traditional weathering steel and 3Ni advanced weathering steel cannot meet the service requirements in the South China Sea environment, necessitating the development of steel with improved corrosion resistance. Alloy steels with Cr of 2.5%-10% (mass fraction) provide a marginal gain in corrosion performance at a low cost and have great potential for marine atmospheric application. A 9%Cr alloy steel was designed to obtain higher corrosion resistance, and the relevant results can offer a reference for developing novel corrosion-resistant steels for the marine atmospheric environment. The initial corrosion behavior of 9%Cr alloy steel in a Cl^- containing environment was investigated using dry-wet cycle test, SEM, TEM, XRD, and electrochemical approaches, and the effects of composite inclusions (Mg, Si, Al)O-MnS and Cr-rich M₂₃C₆ on its local corrosion behavior were discussed. The findings demonstrate that the initial corrosion resistance of alloy steel was more than 12 times that of 09CuPCrNi, and local corrosion occurred during the 360-h dry-wet cycle. Pits' depth below the rust layer followed the lognormal distribution, and the pits' maximum depth (D_max) and average depth (D_ave) with time (t) were in line with the power functions D_max = 8.4844 × t ^0.65717 and D_ave = 7.3181 × t ^0.53866, respectively. The rust layer's compactness and the α / γ^* ratio increased over time, but the addition of high Cr delayed the corrosion. Thus, the rust layer did not entirely cover the surface and only provided limited protection, and an exponent value obtained by fitting the weight loss according to the power function was greater than 1. (Mg, Si, Al)O-MnS caused metastable pitting corrosion through a preferential dissolution of MnS or MgO regions, but its immersion in 2%NaCl solution for 300 min did not induce surrounding matrix's dissolution. The Cr consumption caused by Cr-rich M₂₃C₆'s precipitation was the primary reason for preferentially inducing local corrosion.

Due to the compact passive film, titanium alloys exhibit excellent corrosion resistance. However, during practical applications, the passive film is inevitably damaged by aggressive ions. Among the common ions, F^- is the most harmful to the passive film because of its high complexation with Ti. However, the destructiveness of F^- varies with pH. Moreover, there are inhibitory ions that reduce the aggressiveness of F^-. The acceleration effects of H⁺ and F^- as well as the inhibition effect of Fe³⁺ on the corrosion behavior of TC4 alloy were examined in this work using electrochemical polarization curves measurements and electrochemical impedance spectroscopy (EIS). The results reveal that whereas H⁺ has slight destructive effect on the passive film, F^- has a considerable aggressive effect. In particular, F^- and H⁺ work synergistically to accelerate the corrosion of the TC4 alloy. The addition of Fe³⁺ can somewhat reduce corrosion of the TC4 alloy. This can be attributable to the fact that the faster cathodic reduction caused by Fe³⁺ moves the anodic curves from active-passive region to passive region. Meanwhile, F^- is consumed by forming a compound with Fe³⁺, which mitigates the corrosive effect of F^- on passive film.

Recent development in grain boundary design and control indicates that manipulating the {111}/{111} near singular boundaries will be a promising pertinent to improve the performance against intergranular corrosion attacks for the high stacking fault energy face-centered cubic metals such as aluminum and its alloys. In the current study, five samples of a home-made Al-Zn-Mg-Cu super-high-strength aluminum alloy were rolled at temperatures of 250, 300, 350, 400, and 450^oC, followed by 30 min annealing at 520^oC. A method of grain boundary interconnection characterization based on electron backscatter diffraction and five parameter analysis was utilized to assess the {111}/{111} near singular boundaries in the samples as processed. The preceding rolling temperature was discovered to have a significant impact on the formation of {111}/{111} near singular boundaries during the subsequent annealing at 520^oC, that is, the fraction of {111}/{111} near singular boundaries out of the entire grain boundaries increases at first and then decreases as the preceding rolling temperature increases from 250^oC to 450^oC. In the five samples as processed, the one rolled at 300^oC followed by annealing at 520^oC has a peak content of {111}/{111} near singular boundaries and the fraction reaches 5.0%, which is 10 times higher compared to that of the singular boundaries or namely the coherent twin boundaries. Further investigations reveal that the sample rolled at 300^oC possesses a specific deformation substructure as well as suitable stored energy, resulting in continuous recrystallization during the successive annealing. This type of behavior aids in the formation of {111}/{111} near singular boundaries. The samples rolled at or above 350^oC, on the other hand, exhibit discontinuous dynamic recrystallization, which is detrimental to the development of {111}/{111} near singular boundaries during subsequent annealing. Compared to the sample rolled at 300^oC, the sample rolled at 250^oC has higher stored energy and it improves discontinuous recrystallization during the subsequent annealing. This also harms the formation of {111}/{111} near singular boundaries. Off-line in-situ surface etching test and high-resolution transmission electron microscope (HR-TEM) observation demonstrate that the {111}/{111} near singular boundaries have much higher resistance to intergranular corrosion in comparison to the random boundaries, they possess disclination structures of which the atomic ordering is much higher than that of the random boundaries. The results show that the {111}/{111} near singular boundary is regulable, and to further improving the fraction of such boundaries by manipulating the microstructure evolution will be effective in the practice of how reducing the intergranular corrosion in the aluminum and its alloys.

With the rapid advancements in high-tech aeroengines and gas turbines, surface protective coatings are of increasing interest for enhancing the mechanical and corrosive performances of blade components under harsh high-temperature conditions. Owing to the unique nanolaminate structure, Cr₂AlC coating, a typical Cr-Al-C ceramic comprising MAX phases, provides an excellent combination of metallic and ceramic properties, including high-temperature oxidation resistance and superior damage tolerance. In this work, Cr₂AlC coatings were achieved on nickel-based superalloy substrates using a hybrid deposition system with a cathodic arc and magnetron sputtering source and subsequent annealing. Particularly, the effect of microstructure evolution on the mechanical properties of Cr₂AlC coating was studied under various thermal annealing temperatures of 1073, 1123, 1173, and 1223 K for 2 h. The phase structure, surface morphology, cross-sectional morphology, and elemental distribution of the coatings were characterized by XRD, SEM, and EDS. The mechanical properties, including the hardness and toughness of the coatings, were tested by nanoindentation and Vickers indentation. The results showed that the Cr₂AlC MAX phase was decomposed and transformed into Cr₂Al, Cr₇C₃, and Cr₂₇C₆ phases at higher annealing temperatures, and element diffusion of the coatings was also observed. Moreover, it was noted that the transition in the phase structure did not lead to the misfit of the interface, and the coatings maintained both a high hardness of 11 GPa and elastic modulus of 280 GPa, regardless of the annealing process. The slight decrease in toughness for annealed coatings could be attributed in the formation of brittle chromium carbides and Al element diffusion. Such Cr₂AlC MAX phase coatings are promising candidates as protective materials for wide applications in harsh high-temperatures applications.