The study systematically elucidates the evolution of deformation defects and formation of stacking faults (SFs) during rejuvenation heat treatment (RHT) of a deformed directionally solidified Ni-based superalloy under various typical creep conditions. During high-temperature solution treatment, deformation defects, including SFs, intersected SFs, superdislocations, and dislocations, were effectively reduced within dendritic cores. In contrast, dislocation was hindered by undissolved coarsened gamma ' precipitates in interdendritic regions, carbides, grain boundaries, and pores. The SFs re-nucleate at residual dislocation clusters and propagate continuously through gamma ' precipitates during secondary aging treatment. It is enabled by the combined effects of a lower stacking-fault energy, the availability of residual dislocations for nucleation, and microstructural evolutions including coherent gamma/gamma ' interfaces and narrowed, nearly dislocation-free gamma channels. The work establishes multi-scale mechanistic framework that explains the defects evolution and their intrinsic link to the reemergence of SFs, thereby providing a coherent basis for designing and optimizing RHT.

Stray grain (SG) remains a critical industrial issue in nickel-based single-crystal superalloys. Yet, the precise micro-mechanism of nitrogen-induced SG is still unclear. Therefore, the SG formation mechanism was investigated in alloys with varying Ti (0, 4.1 wt pct) and N (3, 18 ppm) contents by directional solidification using a spiral grain selector, characterized by OM, SEM and EBSD, and supported by JMatPro thermodynamic calculation. The results show that SG formation probability reached 94.4 pct in the 4.1Ti–18N alloy but was 0 pct in 4.1Ti–3N and 0Ti–18N alloys. We reveal that TiN itself does not directly induce SG; rather, it acts as potent nucleation site for blocky MC carbides. The growth of these blocky MC carbides induces solute fluctuations and constitutional supercooling, which, coupled with thermal instabilities in the spiral channel, triggers SG nucleation.

The critical role of low-temperature creep resistance in gas turbine blade durability drives this investigation into the creep deformation mechanisms of directionally solidified (DS) superalloys at 750 degrees C. Through systematic characterization of composition-orientation-microstructure interactions, fundamental relationships governing the primary creep behavior of CM247LC and DZ411 DS superalloys are established. The results suggest that the standard heat-treated CM247LC superalloy exhibits a pronounced primary creep strain along the <001 > direction, mechanistically attributed to the successive formation and propagation of stacking fault (SF) ribbons. In contrast, DZ411 displays a considerably lower primary creep strain due to the effective suppression of SF ribbon propagation, arising from three synergistic factors: a relatively lower volume fraction of gamma ' precipitates, wider gamma channel, and lower SF energy. Crystallographic orientation analysis uncovers distinct low-temperature creep anisotropy, where transverse specimens show a lower primary creep strain compared to longitudinal creep specimens. This anisotropy originates from orientation-dependent Schmid factors variations in {111}< 112 > slip systems, which further impact the nucleation of SF ribbons. Furthermore, the microstructural degradation after thermal exposure significantly affects the low-temperature creep behavior, as both the nucleation and the propagation of the SF ribbons are altered. The present work enhances our understanding of the low-temperature creep deformation of DS superalloys and is expected to provide insights for optimizing their creep deformation behavior.

The large-scale quantitative analysis of α - and β -AlFeMnSi particles present in wrought aluminum alloys through chemical composition analysis is inefficient and time consuming. The morphology and size of α - and β -AlFeMnSi particles in an Al-Mg-Si wrought alloys are quantitatively investigated in this study. The length and width data of the particles were analysed by image processing from scanning electron microscopy and back-scattered electron images. A bimodal distribution of the length:width (l:w) ratio is found by removing ultrafine particles. The model with smaller average l:w ratio is found to be α -AlFeMnSi particles, and the model with larger average l:w ratio is found to be β -AlFeMnSi particles. A critical length:width ratio, which is found to be 2.7 in this paper, is used to discriminate α -AlFeMnSi particles from β -AlFeMnSi particles. In comparison to the EDS results, the α - and β -AlFeMnSi particles can be effectively determined using the l:w ratio with an accuracy rate of up to 95.3.

This study explores the effects of intermediate annealing (IA) on the microstructure, texture, bendability, and deep drawability of an Al-Mg-Si alloy. It is found that that IA induces particle precipitation and static softening, leading to increases of the average size, number density, and volume fraction of both coarse and fine particles, along with a weakening of rolling texture. These effects become more pronounced with rising IA temperature. The changes in particle distribution and texture significantly influence the final grain size and texture, thereby affecting both bendability and deep drawability. The bendability of the IA-treated sheets is improved as the IA temperature increases, due to the changes in texture components from P and CubeND to Cube. Compared to the Non-IA sheet (dominated by Cube texture), the sheet treated with IA at 430 degrees C exhibits better bendability due to refined grain sizes. Introducing IA or increasing IA temperature improves the deep drawability by weakening the texture intensity of the T4P sheets. These results suggest that achieving both high bendability and deep drawability in Al-Mg-Si alloy is feasible by optimizing IA temperature. This study provides an experimental basis for the possibility of broader applications of Al-Mg-Si alloys in the automotive industry.

The influence of crystallographic textures, which was correlated to intermediate annealing (IA) after hot-rolling, on the hemming performance of Al–Mg–Si alloy sheets was investigated in the present paper. Cube (001 < 100 >) texture is developed after IA and is partially retained after cold-rolling, becoming increasingly pronounced as the IA temperature rises, with the particle-stimulated nucleation (PSN) texture predominating in T4P sheets. In contrast, the T4P sheet without prior IA develops a strong Cube texture, but the clustering of Cube-oriented grains leads to deformation incompatibility with surrounding grains. Consequently, the hemming performance of T4P sheet without prior IA is inferior to that of IA-treated sheets. The hemming performance is improved by IA treatment due to the development of the CubeND ( 22° ND-rotated Cube, 001 < 310 >) orientation induced by the PSN effect. And the hemming performance can be further improved by increasing IA temperature, due to coarsening of Mg2Si particles and the increase of effective PSN particles which lead to the increase of volume fraction of CubeND orientation in T4P sheets.

This study systematically investigates the microstructural rejuvenation of a service-exposed directionally solidified nickel-based gas turbine blade through integrated hot isostatic pressing (HIP) and heat treatment. Advanced characterization techniques, including electron backscatter diffraction (EBSD) and quasi-in situ X-ray computed tomography (XCT), were employed to assess recrystallization behavior and pore evolution across different regions of the blade. EBSD analysis revealed that HIP-integrated rejuvenation treatment effectively suppresses recrystallization growth. Concurrently, XCT quantification demonstrated significant pore closure, with the pore volume fraction decreasing from 0.16 % to 0.03 % and a notable size reduction in large pores. Restoration of the gamma' precipitate morphology via dissolution-reprecipitation mechanisms was observed, which resulted in a refined bimodal distribution of secondary and tertiary gamma' precipitates. These microstructural improvements collectively contributed to a substantial recovery of mechanical properties. The creep life improved by a factor of 4 to 13, and low-cycle fatigue life was enhanced by a factor of 2.1-2.7 times compared to service-degraded conditions. Regional differences in microstructural recovery are attributed to the heterogeneous thermo-mechanical environment during service. These findings provide new insights into microstructural damage mechanisms and the rejuvenation pathways in gas turbine blades, offering a promising strategy for extending the operational lifespan of these critical components.

In order to explore the rejuvenation processes and restoration mechanisms of a directionally solidified superalloy applied in industrial gas turbine blades, three rejuvenation treatment regimes, combined with hot isostatic pressing (HIP), were conducted to rejuvenate the damaged microstructure and extend creep life under low temperature/high stress and high temperature/low stress. After only applying a solution rejuvenation treatment, recrystallization occurred and failed to restore creep life at low temperature/high stress (750 °C/610 MPa). The introduction of HIP fulfilled multiple roles: (i) effective pore closure to delay failure; (ii) significant suppression of recrystallization through annihilation and rearrangement of dislocations; (iii) improvement of the adequacy and reliability for high temperature homogenization based on the suppression of recrystallization. An optimized rejuvenation treatment combining HIP with elevated solution temperatures was developed, achieving superior recovery efficiencies of 87.1 and 104.7 pct in creep life under 750 °C/610 MPa and 900 °C/190 MPa conditions, respectively. These results reveal a strong temperature-stress dependence in rejuvenation efficacy, with superior restoration observed under high-temperature/low-stress conditions, offering practical guidance for service-life extension of blades.

The effect of Sn and Cu addition on precipitation and corrosion behavior of Al-1.0Mg-0.6Si alloy are investigated using the hardness, electrochemical measurements, intergranular corrosion (IGC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the peak-aged hardness of Al1.0Mg-0.6Si (-Cu) alloy were enhanced by the addition of Sn, which is related to the acceleration of precipitation. Although the IGC of Al-1.0Mg-Si alloy is not generated by the addition of Sn, the degree of pitting corrosion will be alleviated. The additions of Cu alone increase the susceptibility of IGC. The susceptibility of IGC of Al1.0Mg-0.6Si alloy can further be increased by joint addition of Sn and Cu, which is related to microstructure evolution of grain boundary. The increase in the width of precipitation free zone (PFZ) and distribution of continuous Q phase at grain boundary to from micro-battery accelerates the susceptibility of intergranular corrosion.

The impact of Sn on the natural aging (NA) and artificial aging (AA) behavior of the Al-Mg-Si alloys with high (1.7), balanced (1.0), and low (0.6) Mg:Si ratios was explored via hardness testing, transmission electron microscopy, and atom probe tomography (APT). Additionally, density functional theory (DFT) studies were also undertaken, which revealed a reduction in the binding energy of the Sn-vacancy within the Sn-containing clusters as a result of increasing the Mg atoms within the clusters, indicating that more trapped vacancies can be released to accelerate the development of NA clusters. The APT results revealed that the Mg:Si ratio of NA clusters increased with an increase in the Mg:Si ratio of the alloys. This, together with the DFT results, is supposed to be the reason for the decreasing Sn-induced NA suppression effect with an enhancement in the Mg:Si ratio of the investigated alloys. The APT results revealed that the Sn atoms increased the Mg:Si atomic ratio of the NA clusters. Therefore, addition of Sn led to a greater deviation in this ratio for the NA clusters in alloys with a high and balanced Mg:Si ratio, compared to the beta '' phase, resulting in suppressed precipitation of beta '' during subsequent AA. However, the introduction of Sn resulted in a Mg:Si atom ratio for the NA clusters that was closer in value to that of the beta '' phase in alloys with a low Mg:Si ratio and promoted the precipitation of beta '' during subsequent AA.

In this study, we present a series of innovative single-layer TaC/alpha-C coatings designed for integration into proton exchange membrane fuel cells (PEMFC). These coatings are fabricated on stainless steel (SS316L) substrates employing the magnetron sputtering technique. We systematically explore the influence of varying TaC content and the current applied to the tantalum target on the composition, morphology, and properties of these coatings. Notably, the investigation reveals that the coatings exhibit remarkably low values for interfacial contact resistance (ICR), amounting to 0.56 m omega cm(2), and corrosion current density, measuring at 10.7 nA cm(-2). Subsequently, Single-cell performance of PEMFC test shows that the highest peak power density of TaC/alpha-C coated SS316L bipolar plates is 1003 mW cm(-2) slightly higher than that of graphite bipolar plates, which is 948 mW cm(-2). All the results show that the novel TaC/alpha-C coating is a prospective coating for PEMFC metal bipolar plates.

In proton exchange membrane water electrolyzer (PEMWE), coatings based on Pt demonstrate outstanding performance; however, their elevated cost restricts broader utilization. The application of nonprecious metal coatings frequently compromises either conductivity or corrosion resistance. In this investigation, a range of nonprecious metal-filled Pt-based coatings was fabricated on TA1 through magnetron sputtering. The application of thinner coatings and filler materials led to a significant reduction in Pt usage to 0.051 mg cm(-2) . The conductive Pt surface, along with the wire-like Pt structure integrated within the coating, contributes to remarkable electronic transmission capabilities. The dense and stable oxides generated by the filler metals ensure excellent corrosion resistance. Following a 48-h durability assessment, the application of the coating decreased the interfacial contact resistance of the Ti plate from 90.5 m Omega cm(2) to 2.48 m Omega cm(2), while the dissolution of Ti ions in the corrosive solution reduced from 13.45 ppb to 0.53 ppb. This effective nonprecious metal-filled Pt- based coating presents a novel strategy for minimizing the cost associated with PEMWE bipolar plates.

In this paper, the combined effect of Sn addition and solution treatment temperature on natural aging (NA) hardness behavior and microstructure of Al-0.4Mg-1.0Si alloy were investigated by hardness test, scanning electron microscope (SEM) and scanning transmission electron microscope (STEM). The evolutions of clusters characterized by three-dimensional atom probe (3DAP) during initials stages of NA are also investigated based on the slow in formation of clusters due to Sn addition. The results shown that a Sn-rich particles with round shape retained in Al matrix after quenching treatment when the added Sn content exceeds it limit solubility, which will reduce the Mg content of the designed alloy. The suppression of NA can be enhanced with the increase in the adding Sn content and solution treatment temperature, which is strongly related to the delay of the segregation of Mg and Si to form clusters due to more trapping vacancies by Sn atoms. The addition of Sn also revealed that the segregation of Si during NA is earlier than that of Mg atoms. The Si-rich clusters are formed preferentially during initial stage of NA, and Mg–Si co-clusters are formed after long period of NA. The Mg/Si ratio and average size of Sn-containing clusters in the 0.04%Sn and 0.1%Sn alloy are obviously higher than that of Sn-free clusters regardless of the 1 day NA or 14 days NA as more Mg atoms are dragged into Sn-containing clusters due to strong interaction between Sn and Mg atoms.

Thermal gradient mechanical fatigueThermal gradient mechanical fatigue (TGMF) tests were conducted on thermal barrier-coated (TBC) tubular specimens to investigate the damage behavior of the TBC under close-to-service conditions. Special attention was paid to the cracking behaviorCracking behavior of TBC under TGMF tests with different temperature ranges, mechanical strain ranges, and phase angles including in-phase (IP) and out-of-phase (OP) loading. Crack initiationCrack initiation, propagation, and coalescenceCoalescence within the ceramic top coat (TC) caused TBC failure during IP-TGMF tests with a 300–1000 ℃ temperature range and a mechanical strain range of 0.45–0.65

Proton-exchange membrane (PEM) dry-wet variation during PEM fuel cell (PEMFC) operation markedly affects PEMFC lifespan. Therefore, deeper insights into the mechanical degradation mechanism of PEM require analysis of the membrane dry-wet change process. The stress changes caused by PEM dry-wet variations may induce mechanical failure. In practice, although high-frequency resistance (HFR) is often used to indirectly characterize PEM dry-wet degrees, numerical simulation can effectively analyze the mass transfer inside a PEMFC for parameters that are difficult to measure directly experimentally (such as membrane water content). Additionally, three-dimensional (3D) model validation requires more comprehensive experimental methods. In this study, we validate the simulated resistance distribution results through local electrochemical impedance spectroscopy. We also discuss the mass- and heat-transfer distribution characteristics under different current densities and analyze the influence of these characteristics on local HFR distribution variations. The calculated HFR distribution results show a certain degree of agreement with the experimental results. Due to the membrane self-humidification effect, the position of the minimum HFR value shifts upstream of the cathode at a high current density. The observed change in membrane stress results from variations in membrane water and temperature distributions with changes in current density. Steady-state HFR distribution analysis to uncover the membrane dry-wet variations caused by load changes-which would affect the HFR distribution changes-reveal that the HFR at the air outlet and the membrane dry-wet variations are more pronounced than at other locations due to the influence of reaction rate and gas velocity. Overall, this study demonstrates that 3D simulations can reliably predict the local HFR distribution of PEMFCs, enabling membrane stress variation analysis and providing guidance for fuel cell design and operation.

The proton exchange membrane (PEM) is the core component of PEM fuel cells and plays an important role in isolating gases and electrons during operation; however, PEMs inevitably encounter degradation problems during operation, resulting in weakening or failure of their core functions, thus leading to safety and service life issues. The PEM degradation produces hydrogen crossover and internal short circuit (ISC) currents, which have similar characteristics. Consequently, it is challenging to estimate these two currents and establish a connection between ex situ parameters and actual operation. The safe use of PEM fuel cells requires a distinction between the characteristics of both current types and their generation mechanisms. Our experimental results show that the hydrogen crossover current caused by pinholes during fuel cell operation is influenced by anode overpressure and hydrogen diffuses upon reaching the cathode side of the fuel cell. Meanwhile, the ISC current is influenced by the electrode potential during ex situ testing and fuel cell operation. Compared with the hydrogen crossover current, the efficiency loss due to the ISC current is the “fastest path” because of both currents have different reaction paths. X-ray computed tomography analyses are consistent with the results of the electrochemical tests.

Using atom probe tomography (APT), transmission electron microscopy (TEM), and hardness tests, the effect of Sn and Cu on the evolution of Mg:Si ratios in clusters and subsequent precipitation hardening behavior of pre-aged Al-1.0Mg-0.6Si alloys are investigated, and the underlying mechanism is revealed by density functional theory (DFT) calculation of interaction energy. It is shown that, the doping of Sn and/or Cu increases the average Mg:Si ratio in clusters. This increase is attributed to the strong interaction of Sn/Cu with Mg solutes, which enhances the binding of Mg to Si-rich clusters and results in a higher proportion of clusters with Mg:Si ratios near 1 (0.75–1.25). Consequently, the enhanced precipitation of β'' precipitates during artificial aging is observed in Sn and/or Cu doped alloys, due to the ease of clusters with Mg:Si ratios near 1 transform into β'' precipitates, leading to an improved hardening response. Notably, the combined doping of Sn and Cu exhibits the strongest aggregation tendency towards Mg solutes, yielding the most pronounced strengthening effects on precipitation and hardening response during artificial aging. Furthermore, a schematic model detailing the evolution of Mg:Si ratios in clusters is proposed, based on the APT results and DFT calculation of interaction energy.

The impact of hot rolling finish temperature (HRFT) on the evolution of microstructure, texture, as well as formability—including deep drawability and bendability—of Al–Mg–Si alloy was studied in present work. The obtained results reveal that HRFT has a notable influence on the dynamic softening and dynamic precipitation behaviors during the hot rolling process of the investigated alloy. This leads to the volume fraction and number density of micro-sized Mg2Si particles increase as the increase of HRFT, those of nano-sized particles decrease, and the dislocation density decrease, in the hot-rolled sheets. These microstructural variations persist in the cold-rolled sheets, subsequently affecting the ultimate microstructure, texture, as well as formability of T4P sheets. The deep drawability improves as the HRFT rises, as indicated by the increase in normal anisotropy (r‾) and decrease in planar anisotropy (Δr). This is attributed to the weakening of texture intensity. The bendability, quantified by the minimum hemming factor (Rmin/t), deteriorates as the HRFT rises from 260 °C to 390 °C, attributed to the strengthening of P component along with the weakening of Cube component. Conversely, with the HRFT rises from 390 °C to 420 °C, the bendability improves dramatically due to the significant reduction in the average grain size. A combination of excellent deep drawability and bendability could be obtained by elevating the HRFT to 420 °C, attributed to the combined effect of weakened texture intensity and fine grains.

The effect of coating degradation on the hot corrosion performance of coated alloys was investigated in Na2SO4/ NaCl (75:25, wt./wt.) salt at 900 degrees C. Degraded coatings were obtained by thermal exposure before the hot corrosion test. The results indicate that when the beta-NiAl phases within the coating were completely depleted, the hot corrosion process was delayed due to the Al-rich interdiffusion zone (IDZ) formed after the 900 degrees C thermal exposure to provide Al for the healing of the Al2O3 layer. Nevertheless, the Cr-rich IDZ formed after 1000 degrees C thermal exposure failed to repair the Al2O3 layer, causing the alloy to corrode aggressively even though Cr has been substituted for Al to participate in the corrosion process.

The effect of sulfur on the hot corrosion resistance of Ni-base single crystal superalloy was investigated in Na2SO4 salt at 900 degrees C in static air. The results indicate that the corrosion resistance of the superalloy is significantly degraded even with several ppm contents of sulfur in the alloy. High sulfur content in the alloy causes the oxide layer to bulge and significantly shortens the corrosion incubation period. The accelerated corrosion process is attributed to the outward diffusion of sulfur from the alloy promoting S segregation at the oxide/metal interface and hence favors crack premature initiation.