Promising High-temperature Structural Materials Research Articles

A Novel Preparation Method of (Ti,Zr,Nb,Mo,W)B2-SiC Composite Ceramic Based on Reactive Sintering of Pre-Alloyed Metals

High-entropy diboride-based (MeB2-based) ceramics are promising high-temperature structural materials because of their excellent mechanical properties, high-temperature stability, and oxidation resistance. In order to achieve low-temperature sintering of the high-entropy ceramics, a novel preparation method of high-entropy (Ti,Zr,Nb,Mo,W)B2-SiC ceramics based on reactive sintering of pre-alloyed solid-solution metals and nonmetals of Si, C, B4C was conducted in the current work. Mechanical alloying behavior of the mixed metal powders, as well as the phase composition, microstructure, mechanical properties, and oxidation behavior of the as-sintered MeB2-SiC ceramic were investigated. The XRD, SEM, and EPMA results indicated that the primary MeB2 solid-solution and SiC phases could be successfully formed during reactive sintering at a relatively low temperature of 1650 °C. The as-sintered MeB2-SiC ceramics had a high relative density of 97.8% and high mechanical properties (hardness of 19.74 ± 0.8 GPa, flexure strength of 533 ± 38 MPa, and fracture toughness of 6.01 ± 0.77 MPa·m1/2). Combining the oxidation behavior and microstructure evolution of the oxidation layer, a continuous and relatively dense MeOx-SiO2 oxidation layer was gradually formed and covered on the external surface, leading to decelerating oxidation behavior after an oxidation exposure time of 10 min.

Tailoring the hydrogenated mechanism of Pt3Al from first-principles investigation

Pt–Al compounds are promising high-temperature structural materials. However, the hydrogenated behavior of Pt3Al is still unclear. To explore the hydrogenated mechanism, we apply the first-principles method to investigate the role of hydrogen (H) in Pt3Al. Here, the cubic and tetragonal Pt3Al are considered. Based on the hydrogen occupied position, three H-doped sites are designed in cubic and tetragonal phases. It is found that the hydrogen is a thermodynamic stability in two Pt3Al phases. Compared to the cubic Pt3Al, the hydrogen prefers to occupy the octahedral interstice (H(2) site) of the tetragonal Pt3Al. Importantly, the H-doped Pt3Al is a mechanical stability. In particular, it is found that the hydrogen weakens the volume deformation resistance, shear deformation resistance and elastic stiffness of Pt3Al. But the hydrogen improves the ductility of Pt3Al due to the electronic interaction between hydrogen and Pt3Al. Naturally, the low elastic properties are that the introduction of hydrogen weakens the localized hybridization between Pt atom and Al atom, and forms the H–Pt bond. In addition, the hydrogen also weakens the Debye temperature (θD) of Pt3Al.

Prediction of new stable phases of FePd2 crystal alloy

The stable crystal structures of FePd2 under ambient pressure are explored using the particle swarm optimization technique. In addition to the previously reported tetragonal I4/mmm, orthorhombic Immm and trigonal P3¯m1 phases, three as-yet-unreported phases with R3¯m, Cmcm, and P4/nmm space group are uncovered. Subsequent first principles calculations reveals that all phases have negative enthalpy of formation and the enthalpy of the tetragonal I4/mmm phase is the lowest. Also, these phases are mechanically and dynamically stable. Their ferromagnetism and metal ductility are confirmed by the electronic structure and Pugh's ratio. The bulk modulus of these phases are almost equal, and the I4/mmm structure has the relatively higher Young's modulus and shear modulus. The dimensionless magnetic hardness parameter demonstrated that the I4/mmm and P4/nmm structures are semihard magnets, and the other structures are permanent/hard magnetic materials, in which the Immm, Cmcm, and P3¯m1 structures are the potential candidates for ultra-high density magnetic storage. The results of the bulk modulus and thermal expansion coefficient at finite temperature show that the P3¯m1 structure as a promising high-temperature structural material.

Microstructure and Oxidation Behavior of Nb-Si-Based Alloys for Ultrahigh Temperature Applications: A Comprehensive Review

Nb-Si-based superalloys are considered as the most promising high-temperature structural material to replace the Ni-based superalloys. Unfortunately, the poor oxidation resistance is still a major obstacle to the application of Nb-Si-based alloys. Alloying is a promising method to overcome this problem. In this work, the effects of Hf, Cr, Zr, B, and V on the oxidation resistance of Nb-Si-based superalloys were discussed. Furthermore, the microstructure, phase composition, and oxidation characteristics of Nb-Si series alloys were analyzed. The oxidation reaction and failure mechanism of Nb-Si-based alloys were summarized. The significance of this work is to provide some references for further research on high-temperature niobium alloys.

Effect of Al content on the microstructure and mechanical properties of γ-TiAl alloy fabricated by twin-wire plasma arc additive manufacturing system

TiAl alloys are considered as promising high temperature structural materials. However, the inherent brittleness makes it difficult to be processed. In the present research, TiAl alloys with different Al content are fabricated successfully using an innovative twin-wire plasma arc additive manufacturing system. The effect of Al level on the phase composition, microstructure characteristics, microhardness and tensile properties of as-deposited TiAl alloy is investigated in detail. The results show that the α2 phase content exhibits increase tendency with the decrease of Al level, and the α2 phase content is higher in the top region than that in the middle region. The tetragonal ratio c/a of γ phase tends to reduce with the decrease of Al content. The microstructure characteristics also present obvious difference for as-deposited TiAl alloys. The lamellar spacing gradually decreases with the decrease of Al concentration. With decreasing Al level, the microhardness of alloy tends to increase. In addition, the as-deposited Ti-48 Al (at.%) alloy exhibits much better tensile properties than other TiAl alloys due to optimum microstructure characteristics. The findings provide a valuable reference for additively manufactured TiAl alloy with proper composition ratio.

Enhancing high-temperature strength and ductility of γ-TiAl matrix composites with controllable dual alloy structure

Gamma-TiAl matrix composites can function as promising high-temperature structural materials. In this study, to improve the poor ductility and insufficient strength of composites at high temperatures, they were successfully prepared via powder metallurgy by adding the Ti–6Al–4V alloy. The experimental results indicate that the soft phases of Ti–6Al–4V were surrounded by the hard phase of Ti–48Al–2Cr–2Nb, and the special structure exhibited a unique strain hardening mechanism, which resulted in the high strength and ductility of the composites at high temperature. The 8 wt% Ti–6Al–4V composites were fractured with an elongation approximately 90.65% and tensile strength of 427.75 MPa at 800 °C and 5 × 10−5 s−1; the elongation and tensile strength were both higher than those of single unreinforced Ti–48Al–2Cr–2Nb alloy. Moreover, with an increase in the deformation strain, the deformation behavior started from the Ti–6Al–4V area, which had good ductility. The dislocation movement was hindered by the Ti–48Al–2Cr–2Nb area, and dislocation accumulation and grain deformation occurred, leading to strength increase. The stress concentration and high-density dislocations were stored in the soft phases, which delayed the initiation and propagation of pores and cracks. Moreover, besides grain sliding, evident dislocation activities occurred; therefore, the high ductility of the composites was obtained.

High-temperature oxidation behavior of Co-doped WB2 ceramics in air

With the high melting point, excellent mechanical properties and good thermal stability, WB2 is a candidate of the promising high-temperature structural materials. WB2 ceramics were hot pressed at low temperatures (~1500°C) with a small amount of Co as sintering aids, achieving high relative density and mechanical properties. In this paper, Co-doped WB2 ceramics were selected as test materials to carry out the oxidation experiments systematically. The oxidation resistance of the samples was evaluated at temperatures of 800°C, 1200°C, and 1600°C in static air. At 1200°C and below, Co-doped WB2 ceramics still possessed good oxidation resistance. The oxidation behaviors of the Co-doped WB2 ceramics were studied and the oxidation mechanism was discussed in detail. Besides, the oxidation kinetics of the Co-doped WB2 ceramics at 1200°C were studied. The result showed the oxidation rate of WB2 ceramics basically obeyed a parabolic law at 1200°C. The existence of Co aids was not good for the oxidation resistance of WB2 ceramics, mainly due to the increasing oxygen vacancy concentration of the oxide scale. The phase compositions, the microstructure of the surface and cross section of the oxidized samples were characterized using X-ray diffraction and scan electron microscopy along with energy dispersive spectrometry. Beneath the surface, the oxide scale of Co-doped WB2 ceramics consisted of mainly WO3 skeleton layer and glassy B2O3 layer, which contributed to the good oxidation resistance at 1200°C.

First-principles investigation of structural stability, mechanical and thermodynamic properties of Pt3Zr5 compounds

Pt–Zr compounds are promising high-temperature structural materials due to the high melting point, high strength and excellent oxidation resistance etc. However, the correlation between structure and the related properties of Pt3Zr5 is entirely unclear. Here, we apply the first-principles calculations to study the structural stability, mechanical and thermodynamic properties of Pt3Zr5. Four structures: hexagonal (P63/mcm), tetragonal (I4/mcm), orthorhombic (Pbam) and orthorhombic (Cmcm) are considered. The calculated results show that the four Pt3Zr5 structures are thermodynamically stable at the ground state. In particular, the hexagonal (P63/mcm) phase is more thermodynamically stable than the other three structures. The calculated elastic modulus shows that the tetragonal (I4/mcm) Pt3Zr5 structure has stronger bulk deformation resistance in comparison to the other three structures. However, the hexagonal structure (P63/mcm) has stronger shear deformation resistance and higher elastic stiffness in comparison to the other structures. Naturally, the high mechanical properties of Pt3Zr5 are attributed to the strong cohesive force between Pt layer and the Zr layer. Finally, it is found the calculated Debye temperature of the hexagonal (P63/mcm) is 265.0 K, which is larger than the other structures.

Crystallographic orientation relationships and interfacial structures between reinforcement and matrix phases in an in situ (Ti, Nb)B/Ti2AlNb composite

High-performance (Ti, Nb)B/Ti2AlNb composites are promising high-temperature structural materials for the new generation of aerospace engines. The interfaces between the (Ti, Nb)B reinforcement and matrix phases (i.e. O-Ti2AlNb, α2-Ti3Al and B2 phases) affect the mechanical properties of the composites largely. In this study, the properties of the interfaces were systematically revealed after fabricating a (Ti, Nb)B/Ti2AlNb composite by low-energy ball-milling and spark plasma sintering (SPS). A high-resolution transmission electron microscopy (HRTEM) was adopted to evaluate the crystallographic orientation relationships (ORs) and interfacial structures. (Ti, Nb)B maintains three coherent interfaces with the matrix, and the preferred ORs between them can be expressed as [112¯0]α2//[010](Ti, Nb)B and (1¯100)α2//(100)(Ti, Nb)B; [11¯0]O//[010](Ti, Nb)B and (110)O//(100)(Ti, Nb)B; [11¯1]B2//[010](Ti, Nb)B and (1¯12)B2//(100)(Ti, Nb)B. The results of first-principles calculations indicated that the (1¯100)α2/(100)(Ti, Nb)B interface possesses a higher bonding strength compared with the (110)O/(100)(Ti, Nb)B and (1¯12)B2/(100)(Ti, Nb)B interfaces, and the (Ti, Nb)B reinforcement and the matrix are bonded through strong ionic bonds and weak covalent bonds. Moreover, based on Bramfitt’s lattice mismatch theory, it was found that the (Ti, Nb)B reinforcement acts as an effective substrate in promoting the heterogeneous nucleation and preferred precipitation of the α2 phase. Suppressing the brittle α2 precipitate around the reinforcement improves the ductility of the composite obviously.

Fabrication process and mechanical properties of C/SiC corrugated core sandwich panel

Carbon fiber reinforced SiC composite is a kind of promising high-temperature thermal protection structural material owing to the excellent oxidative resistance and superior mechanical properties at high temperatures. In this work, a novel design and fabrication process of lightweight C/SiC corrugated core sandwich panel will be proposed. The compressive and three-point bending of the C/SiC corrugated sandwich panels are conducted by experiment and numerical simulation. The relative density of as-prepared C/SiC sandwich panel and the density composite material are 1.1 and 2.1 g/cm3, respectively. As the density of the C/SiC sandwich panel is only 52.3% of the bulk C/SiC, suggesting that lightweight characteristic is realized. Moreover, the C/SiC sandwich panel manifests itself as linear-elastic behavior before failure in compression and the strength is as high as 15.1 MPa. The failure mode is governed by the core shear failure and panel interlayer cracking. The load capacity under the three-point bending C/SiC composite sandwich panel is 1947.0 N. The main failure behavior is core shear failure. The stress distribution under the compression and three-point bend was simulated by FE analysis, and the results of numerical simulations are in accordance with the experimental results.

Synthesis of TiAl/Nb composites with concurrently enhanced strength and plasticity by powder metallurgy

TiAl-based alloys with high melting point become the promising high temperature structural materials, but the inherent brittleness drawback suppresses their application. Here, we proposed a controllable strategy to concurrently achieve high strength and high plasticity in TiAl/Nb composites that were prepared by introducing fine plastic Nb particulates to disperse around matrix TiAl, followed by powder metallurgy reaction at 1200 °C/50 MPa/1 h. A complex atomic diffusion reaction (ADR) at the interfaces between matrix TiAl and plasticizer Nb was clarified. The results of uniaxial compression of TiAl/Nb composites at room temperature (RT) show the high strength and excellent plasticity, due to the operation of multiple deformation mechanisms of involved phases in the novel structure. Definitely, the prominent deformation mechanism of matrix TiAl was 1/6112¯]111 ss-slip. The plasticizer, such as fresh Nb-based intermetallics (Nbim) and remained Nb (Nbr), coordinated the overall migration of matrix particulates in the form of compatible deformation. The strengthening phase O/B2 belonged to the dislocation-mediated deformation and was responsible to propagate stress from the plasticizer to the matrix. Predominantly, the tailoring microstructure that Nbim/Nbr was interspersed in the fresh γn and O/B2 was conducive to the successive straining of the composites, which in turn facilitated the intersection or entanglement of the proliferating dislocations and thereby resulted in high strength.

Structural, mechanical, electronic properties of refractory Hf–Al intermetallics from SCAN meta-GGA density functional calculations

Hf–Al intermetallics are novel promising high-temperature structural materials, which exhibit excellent mechanical properties. In this work, the structural parameters, elastic constants, and mechanical anisotropies of Hf–Al intermetallics are investigated by applying the latest meta-GGA functional SCAN as well as several other widely used density functionals such as LDA, PBE and PBEsol. It is found that HfAl2 is the most thermodynamically stable stoichiometric compound among all Hf–Al binary intermetallics. The elastic moduli like B, G, E, ductility index (B/G ratio) and Poisson's ratio (σ) of Hf–Al intermetallics are predicted based on Voigt–Reuss–Hill approximation, indicating most Hf–Al binary intermetallics are brittle except Hf5Al3 and Hf2Al. Besides, the three-dimensional (3D) contour plots of mechanical moduli are provided to characterize the elastic anisotropy in Hf–Al intermetallics. HfAl shows obvious anisotropy in both Young's and bulk moduli along different crystallographic directions, while very weak anisotropy is revealed for both HfAl2 and Hf4Al3 phases since the 3-D surface contours of mechanical moduli show little deviations from isotropic spherical shapes. The calculated electronic properties indicate that relatively high thermodynamic stability of HfAl2 phase is mainly ascribed to the formation of a pseudo-gap in the electron density of states originating mainly from the Al-2p and Hf-5d states at the Fermi level.

In-situ reaction synthesis and mechanical properties of quaternary MAX phase (Cr2/3Ti1/3)3AlC2

Bulk quaternary MAX phase (Cr2/3Ti1/3)3AlC2 was synthesized by in-situ reaction/hot pressing method using Cr, Ti, Al, and C powders as starting materials. The involved reaction routes during hot-pressing were determined according to XRD and SEM/EDS analysis results. The possible chemical reactions involved during hot pressing process were proposed. It was revealed that the desired (Cr2/3Ti1/3)3AlC2 was formed via the reaction between intermediate products of ternary MAX Cr2AlC and carbide TiC, providing another path for the preparation of high order MAX phase. Tests of mechanical properties suggested that the Vickers hardness of (Cr2/3Ti1/3)3AlC2 was 5.6 GPa, higher than that of the ternary MAX phase Ti3AlC2. Its flexural and compressive strength were determined to be 493 MPa and 1407 MPa at room temperature, respectively. Flexural strength maintained a relatively high level of 424 MPa up to 1000 °C, about 90% of that at room temperature. The dependence of elastic modulus on increasing temperatures exhibited similar tendency to that of flexural strength. The as-synthesized (Cr2/3Ti1/3)3AlC2, a unique quaternary layered nano-laminated carbide, was a promising high temperature structural material with its attractively comprehensive properties.

Wire arc additive manufacturing of titanium aluminide alloys using two-wire TOP-TIG welding: Processing, microstructures, and mechanical properties

Titanium aluminide (TiAl) alloys are promising high-temperature structural materials in the aerospace field. Additive manufacturing is a desirable process for fabricating TiAl alloys. In the process of wire arc additive manufacturing of TiAl alloys, Al-based and Ti-based wires were used as the feedstocks. However, it is hard to ensure the two different wires melt synchronously under the heat of one single arc, so the desired microstructures with γ (TiAl) phase and α2 (Ti3Al) phase are hard to obtain. A two-wire TOP-TIG-based additive manufacturing process for TiAl alloys is proposed in this paper. The Ti6Al4V wire and pure Al wire are used as the feedstocks. The Al wire is fed in TOP-TIG mode behind the molten pool, while the Ti6Al4V wire is fed in conventional TIG mode in front of the molten pool. The two wires melt synchronously in a broad range of parameters. The compositions of the component can be controlled by adjusting the two-wire feeding speeds. The main microstructures of the as-fabricated component contain α2/γ lamellae colonies, equiaxed γ grains, and α2 grains. In the top and middle regions, when the Al content is 45 at.%, the structures are full α2/γ lamellae; as the Al content increases to 50 at.%, some equiaxed γ grains distribute at the grain boundaries; the component with 55 at.% Al content exhibits the structures consists of equiaxed γ grains with snowflake-shaped α2/γ lamellae colonies. In the bottom region, all components exhibit the coarse equiaxed α2 grains with γ laths. As the Al content increases, the α2 phase decreases, but the γ phase increases, and from the top region to the bottom region, the volume fraction of the α2 increases by about 19.4 %. The hardness value of the top and bottom regions is higher, and the middle region exhibits the lowest hardness. As the Al content increases, the hardness decreases. The component with 50 at.% Al exhibits the highest compressive strength with 1762 MPa and the largest compressive ratio with 26.1%.

Sol–gel-based coatings for oxidation protection of TiAl alloys

The low density, high specific strength, and good creep properties make TiAl alloys being promising high-temperature structural materials in aerospace and automotive industries. However, the insufficient oxidation resistance limits their extensive practical applications . It is the intention of this review to illustrate the mechanism and development of sol–gel-based coatings, a surface modification approach for oxidation protection of TiAl alloys, but not to present a general review on the oxidation protection of TiAl alloys. The oxidation behavior and mechanism of TiAl alloys were addressed briefly. The discussion focused mainly on the sol–gel coatings preparation method and generation mechanism. Finally, the development trend of sol–gel-based coatings for high-temperature oxidation of TiAl alloys was prospected.

A particle reinforced NbTaTiV refractory high entropy alloy based composite with attractive mechanical properties

Refractory high entropy alloys (RHEAs) are promising high temperature structural materials because of their excellent high temperature strength and high melting point. With introducing secondary particles, the high temperature mechanical properties can be further improved. However, its poor ductility limits the industrial application. In the present work, a new ductile NbTaTiV RHEA-based composite reinforced with Ti-C-O particles were in-situ synthesized through spark plasma sintering (SPS). The composite exhibits excellent room temperature compressive properties with yield strength, ultimate strength and fracture strain of 1760 MPa, 2270 MPa and 11%, respectively. A model is presented to study the strengthening mechanism, and the theoretical calculation shows that the dramatically strength enhancement is mainly due to the in-situ formation of Ti-C-O particles.

Influence of Ir concentration on the structure, elastic modulus and elastic anisotropy of Nb[sbnd]Ir based compounds from first-principles calculations

Although NbIr compounds are promising high-temperature structural materials due to the high melting-point, moderate density and excellent thermal stability, the structural stability and mechanical properties of NbIr compounds are unclear. Here, we investigate the influence of Ir concentration on the structure, elastic modulus, elastic anisotropy and brittle-or-ductile behavior of NbIr based compounds by using the first-principles calculations. Six NbIr compounds are considered. The results show that the structural stability of NbIr compounds strongly depends on the Ir concentration. In particular, NbIr3 is more thermodynamically stable than the other NbIr compounds. The calculated elastic modulus of NbIr compounds (except for Nb5Ir3) increases with increasing Ir concentration. The calculated bulk modulus, shear modulus and Young's modulus of NbIr3 are much larger than that of other NbIr compounds. It is found that the high elastic modulus of NbIr3 is attributed to the strong and symmetrical NbIr and IrIr metallic bonds. Compared to other NbIr compounds, Nb3Ir and NbIr3 have the smallest percentage anisotropy in compressibility. However, Nb3Ir2 has the highest percentage anisotropy in shear. Finally, our work indicates that NbIr3 is a promising high-temperature structural material, which is potential used in advanced aerospace and automotive applications.

Microstructures and mechanical properties of ductile NbTaTiV refractory high entropy alloy prepared by powder metallurgy

Refractory high-entropy alloys (RHEAs) are promising high-temperature structural materials due to their high melting point and extraordinarily high yield strength. However, their industrial application is greatly restricted due to their limited room-temperature ductility. In the present investigation, a ductile and strong single-phase NbTaTiV RHEA was synthesized by powder metallurgy method. Effects of the sintering temperature on the phase formation, microstructural evolution and the mechanical properties of the NbTaTiV RHEA were characterized. The results show that the NbTaTiV RHEA sintered at 1700 °C has an equiaxed single bcc phase microstructure, no obvious porosity and compositional segregation can be observed. The alloy exhibits a relatively high hardness of 510 HV, yield strength of 1.37 GPa, and compressive fracture strength of 2.19 GPa with a high fracture strain of 23% at room temperature. Typical strain softening and steady state flow occur during compressive deformation at high temperatures. During deformation at 1000 °C, the alloy still exhibits high yield strength of 437 MPa with a compression strain over than 40%. The outstanding mechanical properties is mainly attributed to the homogeneous and fine microstructures, and solid solution strengthening effect. It can be concluded that the powder metallurgy is a promising way for preparing ductile RHEAs with outstanding comprehensive mechanical properties.

Microstructure and Mechanical Properties of Particulate Reinforced NbMoCrTiAl High Entropy Based Composite.

A novel metal matrix composite based on the NbMoCrTiAl high entropy alloy (HEA) was designed by the in-situ formation method. The microstructure, phase evolution, and compression mechanical properties at room temperature of the composite are investigated in detail. The results confirmed that the composite was primarily composed of body-centered cubic solid solution with a small amount of titanium carbides and alumina. With the presence of approximately 7.0 vol. % Al2O3 and 32.2 vol. % TiC reinforced particles, the compressive fracture strength of the composite (1542 MPa) was increased by approximately 50% compared with that of the as-cast NbMoCrTiAl HEA. In consideration of the superior oxidation resistance, the P/M NbMoCrTiAl high entropy alloy composite could be considered as a promising high temperature structural material.

Enhanced mechanical properties of W-doped Nb4AlC3 ceramics

The W-doped Nb4AlC3 ceramics [(Nb1-xWx)4AlC3, x = 0–0.0375] were successfully fabricated by in-situ reactive hot-press-aided method using elemental niobium, aluminum, graphite and tungsten powders. The XRD results suggest that the matrix phase (Nb1-xWx)4AlC3 and the second phase (Nb1-xWx)C were simultaneously formed when W was added. The SEM images show that (Nb1-xWx)C is dispersed in the W-doped Nb4AlC3 ceramics matrix. The mechanical properties of Nb4AlC3 were greatly enhanced by W doping. Typically, the (Nb0.975W0.025)4AlC3 exhibits the highest flexural strength (483 ± 21 MPa), fracture toughness (8.5 ± 0.3 MPa⋅m1/2) and Young′s modulus (382 ± 18 GPa) at room temperature (RT), which are increased by 59%, 15% and 30%, respectively, compared with the present Nb4AlC3. The Vickers hardness of (Nb0.9625W0.0375)4AlC3 (4.8 ± 0.2 GPa) is 92% higher than that of Nb4AlC3. The (Nb0.975W0.025)4AlC3 also retains a high flexural strength of 344 ± 4 MPa at 1400 °C (71% of RT value), which is much higher than the RT flexural strength (303 ± 22 MPa) of the present Nb4AlC3. The strengthening effect is attributed to the solid solution of W and the incorporation of the second phase (Nb1-xWx)C. The excellent mechanical properties endow the W-doped Nb4AlC3 ceramics as promising high-temperature structural materials.