Although Sn has been established as an effective microalloying element for suppressing the negative natural aging (NA) effect in Al–Mg–Si alloys, its potential to mitigate the negative NA effect in Al–Mg–Si–Cu alloys remains to be confirmed. This study systematically investigated the role of Sn in the NA of Al–Mg–Si–Cu alloys through hardness measurements, differential scanning calorimetry, and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. Our results demonstrate that the addition of Sn significantly suppresses the adverse impact of NA on the peak-aged hardening capacity during subsequent artificial aging and substantially alleviates early-stage hardening kinetics degradation. Our findings suggest that Sn modifies the nature of the NA clusters in Al–Mg–Si–Cu alloys. A significant proportion of NA clusters in the Sn-added alloy effectively served as heterogeneous nucleation sites for strengthening the precipitates during artificial aging, thereby preserving the precipitate nucleation rates and preventing coarsening at the peak-aging stage. Atomic-resolution energy-dispersive X-ray spectroscopy revealed preferential occupation of Si atomic sites by Sn atoms within the β′ and C/Q′ phases. This investigation provides critical theoretical insights for optimizing alloy design in automotive-body aluminum applications.

The multi-layer oxides formed on surfaces of nickel-based single crystal superalloys are well-documented, yet their precise formation scenarios remain uncovered, since a fine time series of microstructural observations of their dynamic evolution in early-stage oxidation has never been accomplished. Here, we report a refined formation scenario of these oxide sub-layers in a second-generation nickel-based single crystal superalloy. Our findings demonstrate that there are actually 5 distinct oxide sub-layers formed on surface, which are identified respectively as the 1st (Ni0.9Co0.1)O, 2nd NiAl2O4, 3rd CoCr2O4, 4th CrTaO4, and 5th Al2Os sub-layers. However, their temporal formation sequence or scenario differs from their spatial formation sequence: the 5th secondary Al2Os sub-layers appear before formation of the 2nd, 3rd and 4th oxide sub-layers. Notably, upon oxidation gamma-phase areas act as preferential pathways for in-depth oxygen diffusion, facilitating the innermost 5th secondary Al2Os sub-layer to form. Our study provides in-depth insights into a high-temperature oxidation mechanism of superalloys.

Twinning is an important deformation mechanism in body-centered cubic alloys, by which various deformation twins including high-index twins such as {5 8 11}<513> twinning can be introduced. However, the microscopic mechanism of high-index deformation twinning has not been fully understood thus far. Here, we reveal the microstructural evolution of a body-centered cubic alloy under dynamic impact loading. Despite {332}<113> twinning acting as the dominant deformation mode, we observed an unexpectedly large number of high-index deformation twins Based on the high-resolution Electron Backscattered Diffraction results, it is confirmed that high-index deformation twins can be induced by double {332}<113> twinning shear during dynamic impact in a body-centered cubic alloy. Our work provides a novel perspective in understanding the formation mechanism of high-index deformation twins in body-centered cubic alloys.

The influence of natural pre-aging on the microstructure and corrosion behaviour of the subsequent artificially aged 2196 Al-Cu-Li alloy was systematically investigated using quasi-in-situ corrosion testing coupled with advanced electron microscopy characterization. It was found that during conventional T6 artificial aging at 180 ℃, sub-grain boundaries (SGBs) exhibit a significantly higher tendency for heterogeneous nucleation of both T1 and S phases than high-angle grain boundaries (GBs), thereby intensifying local electrochemical heterogeneity and promoting intergranular corrosion (IGC) preferentially along SGBs. Natural pre-aging promotes intragranular nucleation and growth of the plate-shaped T1 phase during subsequent artificial aging, while suppressing the continuity and density of T1 precipitates along GBs and SGBs. As such, the incorporation of natural aging prior to artificial aging markedly enhances IGC resistance while concurrently achieving superior hardness. Quasi-in-situ corrosion experiments reveal that, in T6-aged samples, continuous and coarse grain boundary precipitates undergo rapid anodic dissolution during corrosion, resulting in severe IGC. In contrast, in double-stage aged samples, the fine and discontinuous T1 precipitates exhibit suppressed anodic dissolution and instead undergo preferential dealloying during corrosion.

Next-generation aerospace vehicles demand thermal protection materials that can withstand aerodynamic heating achieving 2000°C, while concurrently maintaining structural flexibility and electromagnetic stealth capabilities—a synergistic performance portfolio that remains largely unattainable with conventional ceramic materials. To address this exigent requirement, flexible multiphase SiC-ZrC-C fibers are designed and fabricated in this work. In situ-formed ZrC nanoparticles preferentially nucleate at SiC grain boundaries and act as pinning phases, suppressing SiC grain coarsening at ultrahigh temperature, while the continuous porous carbon scaffold accommodates mechanical deformation. The resultant fibers demonstrate exceptional thermal stability, characterized by phase stability following exposure at 1600°C for 50 h, as well as retained flexibility even after annealing at 2000°C for 1 h in an Ar atmosphere. Concurrently, the fibers exhibit potent electromagnetic wave absorption capabilities, achieving a minimum reflection loss of −52.60 dB and an effective absorption bandwidth of 5.56 GHz. Besides, continuous fabrication yields large-area fibrous membranes, highlighting the feasibility of large-scale production. The results of this work provide new insights into the design and development of structure-function-integrated thermal protection materials for extreme environments.

Allvac 718Plus (hereafter termed 718Plus) is a polycrystalline nickel-based superalloy developed from the widely used Inconel 718, with the key compositional change being the introduction of cobalt. Despite its commercial use, the site occupancy of Co atoms in delta, eta, gamma ', and gamma '' phases, as well as the influence mechanism of cobalt on the precipitate evolution and mechanical properties of 718Plus, remains insufficiently elucidated. In this study, we systematically investigate the partitioning and role of cobalt in governing grain boundary and intragranular precipitation in polycrystalline 718Plus. The results demonstrate that the majority of the cobalt exhibits a partitioning preference for the gamma matrix. In the delta, eta, gamma ', and gamma '' phases, atomic-resolution EDS analyses and first-principles calculations confirm that cobalt preferentially occupies nickel sublattice sites. Increasing cobalt content lowers the solubility of Ni, Nb, and Ti element in the gamma matrix and promotes their partitioning into the delta, eta, and gamma ' precipitates. This redistribution promotes the formation of the eta/delta phase during solution treatment. An increase in the eta/delta phase fraction not only reduces the volume fraction of the gamma '' phase but also that of the gamma ' phase when the increase becomes excessive during subsequent aging treatment. Consequently, the diminished gamma '' phase fraction enhances plasticity but lowers the tensile and yield strength. Additionally, an excessively high eta/delta phase fraction compromises ductility. These findings provide fundamental insight into the cobalt-mediated precipitation mechanisms in nickel-based polycrystalline superalloys and offer valuable guidance for the design of next-generation high-performance alloy compositions.

The plate-like T1-phase (Al2CuLi) precipitates are the key strengthening precipitates in the AlCuLi alloys for aerospace applications. However, their 3-dimensional atomic structures are still an issue full of controversy, since the Li positions in the T1-phase are difficult to determine with the characterization tools available, and since the frequently observed one-unit-cell-thick T1-phase precipitates are difficult to grow into real 3-dimensional crystals. There exist quite a lot of atomic structural models that need to be clarified or confirmed for the T1-phase. Here, we report that all Li-atoms in the thickened T1-phase precipitates can clearly be visualized, and their crystal structures can be determined precisely, using the integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). It has been demonstrated that three basic atomic structures are observed in multi-unit-cell-thick (MUCT) T1-phase precipitates. Other MUCT ones consist of various combinations of these three basic structures, or they represent distinct orientations of the same structure form. The formation of stacking types of T1-phase precipitates has also been discussed. Our study provides atomic-scale insights into the complex growth mechanisms of T1-precipitates in AlCuLi alloys.

The impurity sulfur embrittlement of Ni-based single alloys has long been wrapped in mystery. In this work, we report for the first time the sulfur-induced precipitation of brittle rhenium-rich & ouml; phase in a model Ni-based single alloy. The results showed that the addition of sulfur gave rise to the precipitation of rhenium-rich & ouml; phase with hexagonal close-packed (HCP) crystal structure in the dendritic cores. Besides, the enrichment of sulfur and nickel elements were detected in the & ouml; phase. The behavior of sulfur-induced precipitation of & ouml; phase was rationalized by the first-principles calculations, which indicates that there is a strong bonding interaction between sulfur and rhenium atoms. This work provides a novel perspective on the understanding of the sulfur embrittlement in Ni-based single alloys.

SiC fibers are widely used in high-temperature structural composites as an important reinforcement. The nearly stoichiometric polycrystalline SiC fibers were subjected to various high temperatures under vacuum to study the formation mechanism of graphite/graphene fibers with core-shell structure. The results indicate that the graphite/graphene fibers consist of dense graphite shell and graphene core with porous 3-dimensional network structure, and the tensile strength of porous graphite/graphene fibers is about 254 MPa. The outermost graphite shell is oriented and the {0001}(Graphite) planes with large spacing are almost perpendicular to the surface of the fibers, which facilitates the release of gases. Graphite maintains a special orientation relationship of <1100 > (Graphite) // <110 > (beta-SiC) and {0001}(Graphite) // {111}(beta-SiC) in the early nucleation stage. As the SiC fibers further decompose, the graphite grows and bends, and its orientation relationship with the beta-SiC disappears. Instead, the graphite with the (0001)(Graphite) planes perpendicular to the non-{111}(beta-SiC) interfaces shows a faster growth rate, higher quality and fewer defects. The volume fraction of the pores in the porous 3-dimensional network graphene core exceeds 55 %, and in some cases reaches 86 %. This characteristic not only reduces the weight of fibers but also increases the potential adsorption capacity of fibers. These findings elucidate the mechanism of decomposition of SiC fibers to form graphite/graphene fibers under high temperatures, offering valuable insights into the development of high-performance SiC fibers or porous graphite/graphene fibers.

The Al-Cu alloy is a historical model alloy system in the physical metallurgy of engineering aluminum alloys. Nevertheless, a few fundamental phenomena of phase transformation occurring in this simple alloy are still not adequately understood. Among all, for instance, the formation mechanisms of its key hardening θ′-phase remain mysterious. There is strong evidence that θ′-precipitates can form from a different high-temperature precipitation pathway, while their formation mechanism via the conventional pathway well-known since 1938 remains to be clarified. Using state-of-the-art electron microscopy, here we report a secondary high-temperature precipitation pathway of θ′-precipitates. It is demonstrated that led by a secondary high-temperature precursor, named θ′S-HTP, very fine θ′-precipitates can form in the undeformed bulk Al-Cu alloys at elevated temperatures (≥ 250 °C). Interestingly is that with Sc-microalloying the surviving rate of meta-stable θ′S-HTP precipitates increases drastically and the formed θ′-precipitates become much finer, significantly enhancing the alloys’ strength and thermal stability. It is also revealed that a θ′S-HTP precipitate can genetically evolve into a θ′-precipitate without having to change its morphology and orientation. Our study provides new insights into understanding the industry bulk alloys’ microstructures and properties.

AlErZr aluminum alloys are important heat-resistant materials, strengthened by the so-called L12 Al3M precipitates (where M represents Er, Zr, or other rare-earth elements). However, the precipitation behaviors associated with properties in such alloys are not yet adequately understood. Here, we report that the mechanical properties of AlErZr alloys can significantly be enhanced by tailoring the microstructure and the volume fraction of Al3(Er,Zr) precipitates with varying Fe-impurities, which are almost inevitable in all aluminum alloys. It is demonstrated that an AlErZr-0.1(wt%)Fe alloy exhibits an optimized strength enhancement in comparison with that of AlErZr-0.05Fe and AlErZr-0.2Fe alloys. This enhancement in strength is ultimately attributed to the increased volume fraction of Al3(Er,Zr) precipitates in the AlErZr-0.1Fe alloy, as revealed by advanced electron microscopy and spectroscopy. It is disclosed that the Al3(Er,Zr) precipitates have a core-shell structure with Al3(Er,Fe) as the core and Al3Zr as the shell. Furthermore, Fe atoms are capable of replacing Er atoms in the Al3Er structure, stimulating a higher nucleation rate of small Al3(Er,Fe) cores and therefore leading to a significant increment in precipitate volume fraction of the alloys. Nevertheless, too much Fe-addition results in significant consumption of Er atoms in forming secondary (AlErFe) phase particles during casting, and will ultimately reduce the number of Al3(Er,Fe) cores in the matrix.

Element Ta is crucial for the Ni-based single-crystal superalloys (NXs), but its oxidation mechanism remains elusive owing to its complex oxidation behavior. This work reveals that the Ta element was transformed into three Ta-related phases i.e., CrTaO4, Ta-W-Re nanoparticles and Ta2O5. A continuous CrTaO4 interlayer is formed between the CoCr2O4 and Al2O3 layers, which could effectively hinder the oxygen inward diffusion and exhibits a good adhesive property that maintains scale integrity. However, the formation of Ta-W-Re nanoparticles and Ta2O5 phases within the Al2O3 layer significantly alters its structural integrity, transforming the continuous and dense protective layer into a porous and discontinuous morphology, thereby reducing the oxidation resistance of the Al2O3 layer.

Silicon carbide (SiC) fibers are widely utilized as critical reinforcements in high‐temperature structural composites; however, the relationship between microscopic defects and mechanical performance after ultra‐high‐temperature annealing remains a mystery. In this work, the near‐stoichiometric high‐crystalline SiC fiber (named as F‐III) were subjected to various annealing conditions to clarify the relationship. The F‐III fiber exhibits excellent thermal stability, with the tensile strength retention of 107.8% and 97.2% after annealing at 1800°C for 50 h and 1900°C for 1 h, respectively, under Ar atmosphere of atmospheric pressure. High‐pressure annealing can prevent the formation of graphite shell and decrease the pores/free carbon size to enhance the operating temperature of SiC fibers, resulting in the tensile strength retention as high as 105.6 % after annealing at 2000°C for 5 h. Interestingly, the transgranular fracture mode of SiC fibers is caused by the presence of randomly distributed pores, approximately 2–4 nm in size, within the β‐SiC grains. The tensile strength of SiC fibers is primarily governed by the thickness of graphite shell and the core pores/free carbon size, with the former having a more significant influence. These findings are helpful to provide a theoretical foundation for developing ultra‐high‐temperature‐resistant SiC fibers.

The Chen-van-Dyck (CVD) formulation as a rigorous numerical solution to the Schrödinger equation has been demonstrated being the only accurate multislice method for calculating diffraction and imaging in low-energy transmission electron microscopy. The CVD formulation not only considers the forward scattering effects but also includes the backscattering effects. However, since its numerical computation has to be performed in real-space, the CVD method may suffer from divergence and inefficiency in computing time, especially when used for low-energy scanning transmission electron microscopy (STEM) image simulation. The present study investigates the influence of cutoff value and slice thickness on the accuracy and efficiency of STEM image simulation using this formula. The results show that a small cutoff value is required in the low-energy regime to ensure accuracy, especially for thick specimens. The optimal slice thickness can be predicted approximately by a simple equation. To speed up STEM imaging simulation by up to 17 times using the CVD formulation, a hybrid computation model incorporating multiple graphic process units (GPUs) is suggested, which is of great significance for quantitative STEM imaging in low-energy transmission electron microscopy. The significance of including backscattering effect in STEM image simulation is estimated in comparison with forward-scattering effect.

Twinning-induced plasticity (TWIP) steels have become important materials in industry owing to the good combination of strength and ductility and high strain hardening rate. The excellent mechanical properties are highly related to the glide of dislocation and deformation twinning. However, the cross-slip behavior of the extended dislocation and the mechanism of deformation twinning are still controversial. Here, the partial dislocation motion and austenite twinning of a high-Mn steel at the early stage of deformation were investigated using in-situ tensile transmission electron microscope (TEM) technique. Results show that a large number of plane glide and cross-slip of extended dislocations can occur at the early stage of deformation. Extended dislocation nodes can be formed as a result of the reaction between adjacent extended dislocations on the same glide plane. In-situ tensile TEM experiments confirm two cross-slip models of partial dislocation: (1) the Friedel-Escaig model, cross-slip based on constriction of extend dislocation and re-dissociation; (2) the Fleischer model, cross-slip involving Lomer-Cottrell dislocation. Based on experimental results and energy calculations, it can be confirmed that the formation mechanism of austenite primary deformation twin induced by partial dislocations is different from that of secondary deformation twin. Grain boundary emits partial dislocation into the grain to form stable stacking fault which induces austenite primary deformation twin. The formation of secondary deformation twin is related to cross-slip of extended dislocation. Only the cross-slip of an extended dislocation containing a 90° partial dislocation can induce the formation of secondary deformation twin by introducing the Frank partial dislocation.

Carbide ceramic fibers are of significant importance for application in the high-tech areas of advanced aircraft engines, aerospace vehicles, and the nuclear industry due to their excellent properties, such as high tensile strength and elastic modulus, excellent high-temperature resistance, and oxidation resistance. This paper reviews the preparation and application of different carbide ceramic fibers, including SiC fibers and transition metal carbide (e.g., ZrC, HfC, and TaC) ceramic fibers. The preparation methods of carbide ceramic fibers are discussed in terms of different fiber diameters, represented by SiC fibers with variable weaving properties and functions due to their differences in diameter. Subsequently, the application of carbide ceramic fibers as high-temperature-resistant structural materials, catalyst carriers, sensors, and supercapacitors are summarized, and strategies for the future development of carbide ceramic fibers are proposed. This review aims to help researchers enhance their understanding of the preparation and utilization of carbide ceramic micro/nanofibers, advancing the development of high-performance carbide ceramic fibers.

分别采用分离式Hopkinson压杆和MTS Landmark电液伺服疲劳试验机对冷轧退火态Fe-20Mn-3Al-3Si相变诱导塑性(transformation induced plasticity,TRIP)钢进行900 s-1～3 500s-1范围内的动态冲击实验和应变速率为3×10-3 s-1准静态压缩实验.采用X射线衍射技术(X-ray diffraction,XRD)、电子背散射衍射技术(electron backscatter diffraction,EBSD)和透射电镜(transmission electron microscope,TEM)等对变形试样的微观组织结构进行表征.结果表明,该TRIP钢表现出正应变速率敏感性,且动态冲击变形的屈服强度明显高于准静态变形的屈服强度.无论是在动态冲击样品还是准静态压缩样品中,都可以观察到大量的ε-马氏体和α'-马氏体,且动态冲击样品中ε-马氏体和α'-马氏体的体积分数明显低于准静态变形样品中ε-马氏体和α'-马氏体的体积分数.在动态冲击样品中,除了能观察到大量的ε-马氏体和α'-马氏体以外,也可以观察到大量的｛1011｝εT孪晶和｛1012｝εT孪晶,并且,｛1011｝εT 孪晶和 α'-马氏体之间的取向关系为(110)α'//(0002)εT,<111>α'//<2110>εT.

本文研究了 Al-7.4Zn-1.5Mg-1.7Cu-1.1Li(wt.％)合金在不同均匀化和固溶处理条件下的显微组织和力学性能.结果表明,该铝合金的铸态组织主要由α-Al基体、Li3CuAl5相和Mg32(Al,Zn)49相构成.为充分溶解第二相,提高过饱和固溶度,需要改善该含Li合金的热处理工艺.优化后的热处理工艺为510 ℃/24 h均匀化处理加510℃/1 h固溶处理.对比发现,使用优化后的热处理工艺可明显减少该合金中第二相颗粒的含量,且不发生过烧.相比传统均匀化和固溶热处理制度(460 ℃/24 h+475℃/1 h),采用新的均匀化和固溶工艺后,合金120 ℃时效峰值硬度提升了 34.3 HV,提升幅度约22％.

通常认为孪晶界是完全共格和无缺陷的,但变形过程中产生的孪晶界往往带有很多缺陷.本文通过高分辨透射电镜观察研究了高锰孪生诱发塑性(twinning induced plasticity,TWIP)钢中形变孪晶界的缺陷特征.结果表明,高锰TWIP钢中形变孪晶界的缺陷包括界面原子台阶、9R结构单元和由于位错和孪晶界相互作用产生的高密度位错.与传统认为9R结构由Σ3 { 112} 非共格孪晶界的分解产生不同,形变孪晶界上9R结构单元由晶界直接发射不全位错形成.位错和孪晶界的交互作用造成了孪晶的退化,并在孪晶界附近产生了大量位错,包括高密度的全位错和Frank分位错.基于形变孪晶界缺陷的电镜表征,分析和总结了高锰TWIP钢的强韧化机制.