Excellent High-temperature Properties Research Articles

High-entropy alloys as magnetic shielding materials in low-frequency wireless power transmission

Soft magnetic materials are required to exhibit high saturation magnetization and low coercivity. Iron-based metal alloys, such as FeMnZn, are commonly used commercial soft magnetic materials with electromagnetic shielding functions. However, these alloys generally exhibit low saturation magnetization, poor high-temperature stability, and significant magnetic losses. In recent years, many research groups have highlighted the excellent soft magnetic properties of high-entropy alloys (HEAs). This study develops new HEA powders with superior soft magnetic characteristics for applications in low-frequency magnetic shielding components. The research found that the FeCoNiSiCuNb HEA, under appropriate ball-milling and annealing conditions, exhibits high saturation magnetization and excellent high-temperature properties, retaining over 50% of its magnetism even at 700K. At an operating frequency of 100 kHz, compared to FeMnZn, the real permeability of the FeCoNiSiCuNb HEA is increased by 2.25 times. Preparing this HEA material as a magnetic shielding material can lead to higher inductance, a coupling coefficient increased to 0.84, and a transmission efficiency improvement of 19%, demonstrating the potential of high-entropy alloys in wireless charging applications.

Thermal processing behaviour and microstructural evolution of high W and high γ’ content extruded nickel-based powder metallurgy superalloy FGH4109

ABSTRACT Nickel-based powder metallurgy superalloys with high W and high γ’ content exhibit excellent high-temperature properties, but their high deformation resistance poses significant challenges for hot processing. In this study, the hot compression behaviour of an extruded nickel-based powder superalloy FGH4109 with high W (6.1%) and high γ’ phase contents (60%) was systematically investigated at temperatures ranging from 1060 ℃ ~ 1140 ℃, strain rates from 0.001 s−1 ~1 s−1, and maximum true strains of 0.7. Combined with the hot working map and the microstructure evolution in different hot working zones, the optimal hot working window for the alloy was determined to be in the temperature range of 1060 ℃ ~ 1140 ℃ and strain rates of 0.001 s−1 ~0.012 s−1, where the power dissipation efficiency η was greater than 0.5, and the dominant deformation mechanism was discontinuous dynamic recrystallisation.

Electrochemical Machining of Micro-Pit Arrays on a GH4169 Alloy with a Roll-Print Mask Using a C6H5Na3O7-Containing NaNO3 Mixed Electrolyte.

GH4169 alloy, a nickel-based superalloy known for its excellent high temperature resistance, corrosion resistance, mechanical properties, and high-temperature tribological properties, is widely used in industrial applications, such as in gas turbines for space shuttles and rocket engines. This study addresses the issue of electrolyte product residue in the electrochemical machining process of a GH4169 alloy by utilizing a C6H5Na3O7-containing NaNO3 new mixed electrolyte. Comparative investigations of the electrochemical behavior and electrolyte product removal mechanisms at different concentrations of C6H5Na3O7 additive in NaNO3 solutions were conducted. The effects of additives, applied voltage, and the rotating speed of the cathode tool on the processing performance of micro-pit arrays on a GH4169 alloy were analyzed. The results indicate that the mixed solution containing C6H5Na3O7 significantly improves the localization and geometric morphology of the micro-pits compared to a single NaNO3 solution. The optimal electrochemical machining parameters were identified as 0.5 wt% C6H5Na3O7 + 10 wt% NaNO3 mixed electrolyte, 12 V applied voltage, and 0.1 r/min rotating speed of the cathode tool. Under these conditions, high-quality micro-pit arrays with an average diameter of 405.85 μm, an average depth of 87.5 μm, and an etch factor (EF) of 1.67 were successfully fabricated, exhibiting excellent morphology, localization, and consistency.

Grain boundary crystallography and segregation in Ni-based superalloy INC738 manufactured by electron-beam powder bed fusion in as-built and annealed conditions

The excellent high-temperature properties of Ni-based superalloy INC738 are due to its hierarchical microstructure, making it an ideal engineering material for high-temperature applications. Engineering parts are now increasingly made via electron beam powder bed fusion (EPBF), an additive manufacturing technique suitable for such hard-to-weld Ni-based superalloys, due to lower thermal gradients and unmatched scan path control. The thermal cycles induced by EPBF impact characteristics of the γ-matrix, γ’ precipitates, secondary phases such as carbides, grain boundary (GB) solute segregation and, in turn, properties including GB cohesion and strength. However, a more thorough understanding of the GB microstructure evolution with focus on GB chemistry and character is required to optimise properties. We systematically investigate texture, grain structure, GB habit planes, and GB segregation in INC738 fabricated with linear versus random EPBF scanning strategies. We show that random scanning is a suitable strategy to inhibit cracking, refine grains, and decrease segregation of Cr, Mo, C, and B at GBs. For both scanning strategies, γ/γ GBs predominantly terminate on {100} planes and are decorated with C, B, Mo, and W. Upon 2 h annealing at 1180 °C and 1250 °C, the GB character and texture are shown to remain stable despite a reduction in GB interfacial excess. After 24 h annealing at 1250 °C, GB segregation and depletion are nearly eradicated, while static recrystallisation is observed with a predominant formation of annealing twins and GBs terminating on {111} planes. These findings are critical for defect-free additive manufacturing of INC738 and similar grades for superior high-temperature performance.

Enhancement of thermo-oxidative stability of polyimide composites by functionalized polyimide film surface modification

Polyimide (PI) resin-based composites exhibit excellent high-temperature resistance, solvent resistance, and mechanical properties, making them have broad application prospects in various fields such as aviation, aerospace, and transportation. With the continuous development of new devices, the requirements for the service temperature and service life of materials are improved, so there is an urgent need to improve the thermo-oxidative stability of polyimide composites. In this work, PI films, aluminum-coated PI film, and copper-coated PI film with low oxygen permeability were used as surface oxygen barrier materials, and surface film modified polyimide composites were prepared. The results show that, compared with the unmodified composite materials, after aging at 350°C for 400 hours, the weight loss rates of the composites modified by three kinds of surface films all increased by more than 50%, and the bending strength retention rates of the composites respectively increased by 47%, 51%, 45%, and the interlaminar shear strength retention rates respectively increased by 107%, 82%, 78%, showing excellent thermo-oxidative stability.

Enhancement of sintering and mechanical properties of alumina-rich Al2O3-MgO-CaO refractory composite by doping La2O3

Ceramics or refractories prepared in the Al2O3-rich corner of the Al2O3-MgO-CaO system show excellent high-temperature mechanical properties and chemical stability because of the presence of spinel (MgAl2O4) and calcium hexaluminate (CaAl12O19). However, the densification of these two crystals usually requires high firing temperatures due to their poor sinterability. To address this issue, La2O3-doped MgAl2O4-CaAl4O7-CaAl12O19 refractory composites were designed, and the influence of the doping level on the densification, microstructure, and mechanical properties of the composite was investigated. It was found that the doped La3+ was predominantly dissolved in the CA6 grains by replacing Ca2+, forming uniform solid solutions regardless of doping concentration. This reaction significantly accelerates ion diffusion and CA2 grain growth. Besides, it reduces the aspect ratio of CA6 crystals, weakening the negative effect of the elongated grains on mass transfer and sintering. As a result, the relative density increases from 79.5 % to 95.1 % after sintering at 1600 °C with doping only 0.5 wt% La2O3 into the composite, producing a uniform and dense microstructure with regular angular grains. The above effects result in a significant improvement in flexural strength and fracture toughness (increasing by 61 % and 57 %, respectively). Moreover, the La2O3-doped refractory composite achieves a decline of the high-temperature creep rate by one order of magnitude at 1600 °C.

Research status on the effect of energy density on the forming microstructure and properties of nickel-based superalloys for laser additive manufacturing

Abstract Nickel-based superalloys have excellent high-temperature mechanical properties, corrosion resistance and oxidation resistance, and strong machinability. It is widely used in aerospace, submarine and shipbuilding, petrochemical, electronic industry and other industries. However, there are still challenges in the popularization and application of nickel-based superalloys for alloy components with complex structures and extremely harsh working conditions. In this paper, the research status of the influence of energy density on the microstructure and properties of laser additive fabrication of nickel-based superalloys at home and abroad is reviewed. The influence of energy density on the microstructure evolution behavior and mechanical properties improvement effect of laser additive manufacturing nickel-based superalloys is summarized. The mechanism of energy density was discussed from the perspectives of microstructure evolution and macroscopic performance change. Based on the individual effects and synergistic effects of each process parameter, the influence of laser energy density on dendrite growth, phase precipitation characteristics, element distribution and porosity defect control effect of nickel-based superalloy was expounded, as well as the influence mechanism on microhardness, wear resistance and residual stress. Finally, the energy density optimization and development prospect of laser additive fabrication of nickel-based superalloys are prospected.

Thermal-Mechanical Coupling Performance of Heat-Resistant, High-Strength and Printable Al-Si Alloy Antisymmetric Lattice Structure.

The unsatisfactory mechanical performance at high temperatures limits the broad application of 3D-printed aluminum alloy structures in extreme environments. This study investigates the mechanical behavior of 4 different lattice cell structures in high-temperature environments using AlSi12Fe2.5Ni3Mn4, a newly developed, heat-resistant, high-strength, and printable alloy. A novel Antisymmetric anti-Buckling Lattice Cell (ASLC-B) based on a unique rotation reflection multistage design is developed. Micro-CT (Computed Tomography)and SEM (Scanning Electron Microscope) analyses revealed a smooth surface and dense interior with an average porosity of less than 0.454%. Quasi-static compression tests at 25, 100, and 200°C showed that ASLC-B outperformed the other 3 lattice types in load-bearing capacity, energy absorption, and heat transfer efficiency. Specifically, the ASLC-B demonstrated a 51.56% and 44.14% increase in compression load-bearing capacity at 100 and 200°C compared to ASLC-B(AlSi10Mg), highlighting its excellent high-temperature mechanical properties. A numerical model based on the Johnson-Cook constitutive relationship revealed the damage failure mechanisms, showing ASLC-B's effectiveness in preventing buckling, enhancing load-transfer efficiency, and reducing stress concentrations. This study emphasizes the importance of improving energy absorption and mechanical performance for structural optimization in extreme conditions. The ASLC-B design offers significant advancements in maintaining structural integrity and performance under high temperatures.

Insight into microstructure evolution of in-situ ZrB2np/AA6111 composites with both excellent room and high temperature properties

With rapid development of aerospace and automobile, the service condition of structural components becomes increasingly harsh, diverse and high mechanical properties are urgently needed. In this work, an advanced in-situ ZrB2np/AA6111 composite with excellent room and high-temperature properties was prepared via Al-Zr-B reaction system. The microstructure revealed that ZrB2 nanoparticles with regular polygonal shapes ranged from 10 to 150 nm approximately, and a good α-Al/ZrB2 interface bonding was confirmed. The agglomeration of ZrB2 particles was significantly weakened during hot extrusion. Due to the inhibiting effect on dislocation motion and pinning effect on grain boundaries induced by ZrB2 particles, fine recrystallized grains were obtained in ZrB2/AA6111 composites after extrusion. Compared with AA6111 matrix alloy, the yield strength, ultimate tensile strength and elongation of AA6111-3ZrB2 composites at room temperature and 300 °C were increased by 18.9 %, 12.7 %, 50.0 % and 34.1 %, 22.4 %, 42.4 %, respectively. An excellent room and high-temperature strengthening effect was simultaneously achieved assisted by ZrB2 particles. The improvement of room-temperature properties was mainly owed to the Grain refinement and Orowan bypassing strengthening mechanisms. The good high-temperature properties mainly relied on the superior coarsening resistance of ZrB2 particles which could fully played the Orowan strengthening effect and well protected the grain boundaries at high temperature. This work provides a feasible approach to design high-performance aluminum alloys and is beneficial for the further development of modern industries.

High strength and tackling structural relaxation by sub-grains synergistic deformation in W-Re alloy

The reduction of strength and ductility due to structural relaxation induced by high-temperature annealing has greatly limited the application of tungsten-based alloys in structural functional applications. In this study, W-25(wt%)Re (WRE) alloy, which exhibits significant yielding behavior and tensile strength above 1.4 GPa at room temperature(RT), was successfully prepared by a combination of wet-chemical and rotary swaging process. After annealing at 1000 °C, WRE has an ultimate tensile strength (UTS) of 1253 MPa and total elongation (TE) of 9.8 % at 200 °C. Furthermore, following annealing at 1400 °C, WRE exhibits a UTS of 897 MPa at 500 °C, thereby demonstrating excellent resistance to annealing embrittlement and high-temperature strength. Microstructural analysis reveals that WRE retains a substantial number of fine subgrains and a considerable proportion of low-angle grain boundaries (LAGBs) following high-temperature annealing. The structural stability of WRE enables it to exhibit excellent high-temperature mechanical properties.

Design of a Thermally Stable Heat-Resistant (Al2O3+Al3Ti)/Al Composite with Excellent High-Temperature Mechanical Properties: Multimechanism Synergistic Strengthening Strategy.

The effectiveness of the room-temperature strengthening strategy for aluminum (Al) is compromised at increased temperatures due to grain and precipitate phase coarsening. Overcoming the heightened activity of grain boundaries and dislocations poses a significant challenge in enhancing the high-temperature strength through traditional precipitation strengthening. This study presents novel strengthening strategies that integrate intergranular reinforcements, intragranular reinforcements, refined grain, and stacking faults within an (Al2O3+Al3Ti)/Al composite prepared using sol-gel and powder metallurgy technology. Excellent high-temperature tensile properties are achieved; also, a remarkable fatigue performance at increased temperatures that surpasses those of other existing Al alloys and composites is revealed. These superior characteristics can be attributed to its exceptionally stable microstructure and the synergistic strengthening mechanisms mentioned above. This work offers new insights into designing and fabricating thermally stable Al matrix composites for high-temperature applications.

Effect of heat treatment solid solution temperature on high-temperature performance and diffusion welding tissue of IC10 superalloy

Abstract IC10 superalloys with small pressure and large gaps were welded by TLP diffusion welding. Based on this, the effects of heat treatment on the weld organization and welding performance of IC10 joints were discussed. The results showed that when SBM-3 was used as intermediate solder, the weld structure was similar to that of base metal under the welding process of 1250°C, 0.2 MPa, and 6h. The tensile strength was 133.7 MPa at the temperature of 1100°C. After heat treatment mechanism A, in the joint structure, a larger volume concentration of γ+γ′ phase existed in the weld, smooth transition from base metal to welded joint. Under the heat treatment mechanism A, the tensile strength at 1100°C high temperature can reach 204.6MPa (more than 85% strength of IC10). The appropriate heat treatment mechanism can get small enough micro holes and low enough porosity joints, ensuring the excellent high-temperature mechanical properties of high-temperature alloy.

Long-term aging behavior and mechanism of CMSX-4 nickel-based single crystal superalloy at 950 ℃ and 1050 ℃

Nickel-based single crystal superalloys CMSX-4 have been widely used to manufacture aeroengine turbine blades because of their excellent high-temperature comprehensive properties. The microstructure evolution behavior, mechanism, and influence on micromechanical behavior of the second-generation nickel-based single crystal superalloy during long-term aging at 950°C and 1050°C for 10–2000 h were investigated. The results show that, with the extension of aging time, the average size of γ' phase increased, whose morphology changed from square block to strip and L shape and rafting phenomenon was observed. The coarsening of γ' conforms to Lifshitz–Slyozov–Wagner (LSW) theory and the coarsening rates are 4.241×10−5 and 9.954×10−5μm3/h at 950°C and 1050°C, respectively. After aging at 950°C and 1050°C for 1000 h, segregation of refractory elements was formed in the samples. There are hard topological close-packed (TCP) phases surrounded by γ' envelope precipitates, which destroyed the continuous structure of γ'. The precipitation of TCP caused the depletion of refractory element Re in the γ' envelope phases, resulting in softening effect. It was also found that high temperature can not only accelerate the coarsening of γ' phase but also promote the precipitation and growth of TCP phases.

Exploring high corrosion-resistant refractory high-entropy alloy via a combined experimental and simulation study

Refractory high-entropy alloys (HEAs) have attracted considerable attention due to their stable phase structure and excellent high-temperature properties. In this work, we performed first-principles calculations, coupled with experiments, to explore HEAs with high corrosion resistance. The results revealed that TiNbTa-based HEAs exhibited a lower tendency for corrosion. However, the appearance of local chemical fluctuations (LCFs) increased the corrosion tendency of TiNbTa-based HEAs. Comprehensive SHapley Additive exPlanations analyses uncovered that in a sample with configurational LCFs, the atomic order near the surface was altered. Therefore, corrosion behavior was affected. Based on experiments, the annealed samples exhibited typical chemical segregation and declined corrosion resistance.

Realization of ultra-high temperature stability and excellent electrical properties in LTO-based ceramics via A/B-site co-doing

La2Ti2O7 (LTO) ceramics, ideal for ultra-high temperature applications with a Curie temperature near 1460 °C, were previously limited by a low piezoelectric coefficient (d33) of 1.5 pC/N. In this work, the incorporation of Bi3+ and V5+ dopants have been employed to augment the piezoelectric properties of LTO. An enhanced d33 ∼ 4.0 pC/N is achieved in La1.91Bi0.09Ti1.97V0.03O7 (LBTV9) ceramics, while maintaining an ultra-high Curie temperature of 1437 °C. This improvement is attributed to local heterogeneity in the lattice structure induced by the doping. LBTV9 ceramics also exhibit excellent high-temperature stability and insulation properties, maintaining a d33 at 4.0 pC/N after annealing at 1000 °C for 48 h and stabilizing at 4.2 pC/N across temperatures from 200 °C to 1600 °C, with a DC resistivity of 1.7 × 106 Ω·cm at 1000 °C. These enhancements make LBTV9 ceramics suitable for extreme condition applications, thus unlocking new possibilities for their use in ultra-high temperature piezoelectric devices.

Preparation, Deformation Behavior and Irradiation Damage of Refractory Metal Single Crystals for Nuclear Applications: A Review.

Refractory metal single crystals have been applied in key high-temperature structural components of advanced nuclear reactor power systems, due to their excellent high-temperature properties and outstanding compatibility with nuclear fuels. Although electron beam floating zone melting and plasma arc melting techniques can prepare large-size oriented refractory metals and their alloy single crystals, both have difficulty producing perfect defect-free single crystals because of the high-temperature gradient. The mechanical properties of refractory metal single crystals under different loads all exhibit strong temperature and crystal orientation dependence. Slip and twinning are the two basic deformation mechanisms of refractory metal single crystals, in which low temperatures or high strain rates are more likely to induce twinning. Recrystallization is always induced by the combined action of deformation and annealing, exhibiting a strong crystal orientation dependence. The irradiation hardening and neutron embrittlement appear after exposure to irradiation damage and degrade the material properties, attributed to vacancies, dislocation loops, precipitates, and other irradiation defects, hindering dislocation motion. This paper reviews the research progress of refractory metal single crystals from three aspects, preparation technology, deformation behavior, and irradiation damage, and highlights key directions for future research. Finally, future research directions are prospected to provide a reference for the design and development of refractory metal single crystals for nuclear applications.

Significantly Enhanced Mechanical, Thermal, and Ablative Properties of the Lightweight Carbon Fabric/Phenol-Formaldehyde Resin/Siloxane Aerogels Ternary Interpenetrating Network.

Lightweight ablative thermal protection materials (TPMs), which can resist long-term ablation in an oxidizing atmosphere, are urgently required for aerospace vehicles. Herein, carbon fabric/phenol-formaldehyde resin/siloxane aerogels (CF/PFA/SiA) nanocomposite with interpenetrating network multiscale structure was developed via simple and efficient sol-gel followed by atmospheric pressure drying. The ternary networks structurally interpenetrating in macro-, micron-, and the nanoscales, chemically cross-linking at the molecular scale, and silica layer generated by in situ heating synergistically bring about low density (∼0.3 g cm-3), enhanced mechanical properties, thermal stability, and oxidation resistance, and a low thermal conductivity of 81 mW m-1 K-1. More intriguingly, good thermal protection with near-zero surface recession at 1300 °C for 300 s and remarkable thermal insulation with a back-side temperature below 60 °C at 20 mm thickness. The interpenetrating network strategy can be extended to other porous components with excellent high-temperature properties, such as ZrO2 and SiC, which will facilitate the improvement of lightweight ablative TPMs. Moreover, it may open a new avenue for fabricating multifunctional binary, ternary, and even multiple interpenetrating network materials.

Ti4+ doped high-entropy fluorite oxide ceramics ((ZrHfCeYEr)(1-x)/5Tix)O2-δ: Thermal, mechanical and cyclic thermal shock resistance properties studies

High-entropy fluorite oxide ceramics are promising candidates for spacecraft applications due to their excellent high-temperature thermal-mechanical properties. In this work, four kinds of high-entropy fluorite oxide ceramics ((ZrHfCeYEr)(1-x)/5Tix)O2-δ (HEFOs, x = 0, 0.025, 0.05, 0.075) with different Ti4+ contents were successfully synthesized through solid-state reaction method with conventional sintering. They all exhibited phase stability when annealed at 1500 ℃ for 20 h. When the content of Ti4+ was increased to x = 0.075, the thermal conductivity reduced to1.34 W·m−1·K−1 at 1100 ℃, and the hardness and elastic modulus increased to 14.01 GPa and 205.70 GPa, respectively. Furthermore, the cyclic thermal shock resistance of HEFOs at different temperatures was investigated. The initial flexural strength reached 219.03 MPa when the content of Ti4+ was increased to x = 0.075. After 60 thermal shock cycles at 1200 ℃ and 1500 ℃, the residual strength ratios were 97.56 % and 83.36 %, respectively. The results of this study establish the foundation for future applications of high-entropy fluorite oxide ceramics in spacecraft hot-end components.

High strength and elongation of Mg-Gd-Nd-Zr alloy obtained by synergistic action of high-speed extrusion and short-time aging treatment

Magnesium–gadolinium (Mg–Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth (RE) elements may promote the formation of secondary phase for better-strengthened properties. Herein, novel Mg-7Gd-2Nd-0.5Zr (wt%) alloys were prepared by synergistic reaction induced by high-speed extrusion (EX) and short-time aging treatment (AT). The microstructures, textures, and mechanical properties of the resulting alloys were then comprehensively studied by various analytical methods. The result reveals that the as-cast Mg-7Gd-2Nd-0.5Zr (wt%) alloy is composed of α-Mg matrix and Mg5(Gd,Nd) phase with bony and continuous networks at grain boundaries. The microstructure presents coarse deformed grains and fine recrystallized grains after high-speed EX, and formation of typical (0001)∥ ED extruded fiber texture and [1¯21¯1] RE texture is observed. The EX22 sample exhibits more Mg5(Gd,Nd) precipitated phases, fuller DRXed grains, and shorter peak aging times than the EX9 sample. After the AT at 250 °C, the proportion of deformed grains decreases due to static recrystallization, which leads to a reduction in the average grain size and weakening of the texture intensity. Therefore, combined effect of all strengthening mechanisms aids in achieving balance of high-strength and high-elongation for Mg-7Gd-2Nd-0.5Zr (wt%) alloy. The values of yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of EX22-A sample at room temperature are found to be 292.5 MPa, 350.6 MPa, and 24.3%, respectively. Overall, this study provides relevant experimental basis and theoretical guidance for the development of high-strength Mg-RE alloys, which are useful for future consideration.

New lightweight and super-hard refractory high-entropy alloys developed by a high-throughput method

Lightweight refractory high-entropy alloy (LRHEA) is one of potential structural materials in aerospace industry for its excellent high-temperature comprehensive properties and low density. In this work, a new high-throughput method to develop LRHEAs was proposed. The equimolar HfNbTaTiZr alloy was immersed with melting pure aluminum for a given time, and a thick layer with composition gradient was obtained. Further characterizations of the layer result in relations between composition and nanohardness or Young's modulus, which facilitate the selection of the optimal composition with desired properties. Finally, three LRHEAs were designed and casted into bulk samples with arc-melting method. The alloys show superhigh Vickers hardness of 8.29–9.56 GPa and low densities of 6.27–7.08 g/cm3, showing great potentials in applications as wear-resistant materials. The high-throughput method developed here may also accelerate the development of new LRHEAs.