High-entropy carbide (HEC) ceramics have emerged as promising candidates for ultra-high-temperature structural materials due to their exceptional thermal stability, high hardness, and strong resistance to oxidation and ablation. In this work, we systematically investigate a five-component HEC system, (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C-x, with a focus on achieving low-temperature densification and property optimization via carbon stoichiometry control. Nanocrystalline powders were synthesized via high-energy mechanical alloying (MA) and subsequently densified using spark plasma sintering (SPS) at temperatures ranging from 1500 to 1800 degrees C, with carbon contents varying from x = 0.7-1.0. The results demonstrate that MA successfully produced a single-phase face-centered cubic solid solution with an average grain size of approximately 8.4 nm. SPS conducted at 1700 degrees C yielded high relative densities (>98%) while preserving the single-phase structure, achieving near-full densification at a temperature significantly lower than that typically required by conventional solid-state reaction routes. Notably, the lattice parameter systematically decreased with increasing carbon content. Both hardness and fracture toughness initially increased and then decreased, attaining maximum values of 23.7 GPa at x = 0.8 and 6.2 MPa.m(1/2) at x = 0.9, respectively. This study demonstrates that the combination of MA and SPS enables low-temperature densification of HECs, while carbon stoichiometry serves as an effective handle for tailoring mechanical performance, establishing a foundation for their application in advanced structural and tool materials.

The stability of strengthening precipitates largely determines the high-temperature capability of advanced structural alloys. In the present work, particular attention is given to the coarsening behavior of coherent L12 nanoprecipitates (L12-NPs) in a Fe47Cr16Ni26Ti6Al5 medium-entropy alloy (MEA) subjected to prolonged aging between 700 and 800 °C (up to 350 h). Despite extended thermal exposure, these NPs remain remarkably resistant to coarsening. Their growth behavior is well described by classical Lifshitz-Slyozov-Wagner (LSW) kinetics, which is associated with volume diffusion; however, the corresponding rate constants are reduced by two to three orders of magnitude compared with those typical of Ni-based superalloys. An activation energy of 268 ± 10 kJ mol−1 is obtained, pointing to a diffusion process primarily limited by Al and Ti. Even after long-term aging, the precipitate-matrix interface retains full coherency, accompanied by an exceptionally small lattice misfit of only 0.37%, as evidenced by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy observations. Such stability can be traced to pronounced Ti partitioning (KTi = 18.45) together with an unusually low interfacial energy of 1.83 mJ m−2. These microstructural features translate directly into a typical age-hardening response, with peak yield strengths reaching 1068 MPa at 750 °C and 785 MPa at 800 °C. Strengthening is dominated by precipitate shearing, in which ordering effects play a central role. Collectively, the results indicate that the concurrent presence of minimal lattice misfit, reduced interfacial energy, and strong elemental partitioning effectively suppresses coarsening, thereby ensuring outstanding thermal stability in this cost-efficient MEA.

The potential of tungsten (W)-based high-entropy alloys (HEAs) as plasma-facing materials (PFMs) for future fusion reactors has been evaluated through an investigation of fuzz growth. W-based HEAs (WTaCrV, WTaCrVTi) and pure W fabricated via mechanical alloying and high-pressure sintering have been exposed to helium (He) plasma at 1073 K with an ion energy of 60 eV. After He plasma exposure, all samples exhibit fuzz nanostructures. Detailed analyses of fuzz length, He bubble size, and elemental distribution within the fuzz nanostructures are conducted. The two W-based HEAs demonstrate distinct advantages, exhibiting fuzz lengths reduced by 37.1% (WTaCrV) and 34.3% (WTaCrVTi), alongside smaller He bubble sizes compared to pure W. However, no significant differences in fuzz length or He bubble size are observed between WTaCrV and WTaCrVTi. Significantly, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) analysis reveals that the fuzz nanostructures predominantly comprise W and Ta, attributed to the preferential nucleation and growth of He bubbles in regions enriched with these elements. These findings provide critical insights into the underlying mechanisms governing fuzz formation in W-based HEAs. The superior resistance to fuzz growth in these W-based HEAs guides the design and development of PFMs in future fusion reactors. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

As one of refractory high-entropy alloys (RHEAs), VNbMoTaW is considered to be a promising candidate for elevated-temperature application. However, its creep behavior is rarely reported. In the present work, the compressive creep behaviors of an equiatomic VNbMoTaW RHEA with a grain size of 138 & PLUSMN; 36 mm were well studied over an intermediate temperature range (973-1173 K) and under high applied stress (130-520 MPa). The stress exponent of the alloy is found to remain stable (-1) at relatively low temperatures (973 -1073 K), whereas a stress-dependent transition behavior occurs at high temperatures (1123-1173 K), i.e., the stress exponent of the alloy changes from -1 in the low stress region (130-390 MPa) to - 4 in the high stress region (390-520 MPa). Meanwhile, the creep activation energy increases from 139 to 156 kJ mol-1 at low temperatures to 307-373 kJ mol-1 at high temperatures. The low stress exponent and low activation energy at low temperatures suggest that the creep is controlled by dislocation pipe diffusion. The low stress exponent and relatively high activation energy in the high-temperature low-stress region suggest that the creep is controlled by lattice diffusion. In the high-temperature high-stress region, the prevalent dislocations detected by the post-mortem microstructural observation, the high stress exponent, and high activation energy suggest that the creep deformation is controlled by a lattice diffusion mediated dislocation climb process. These findings provide a fundamental understanding of the creep behavior and deformation mechanism of VNbMoTaW, which can be applied to design advanced creep-resistant RHEAs. & COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC

High-entropy carbides (HECs) are novel advanced materials composed of covalently bonded multicomponent transition metals and carbon. The transition metal atoms of all the precursor components are randomly distributed at the cation sublattice. Recently, a series of HECs with a non-stoichiometric compound (NSC) as one of the precursors have been synthesized. However, the effect of vacancies on the formation of HECs has not been addressed well. In this paper, NbC0.5 was selected as the NSC to study the interfacial diffusion behavior of NbC0.5 and other covalent transition metal compounds (MCs: M represents one of V, Ti, Ta, and W). The presence of vacancies resulted in a carbon concentration gradient, reduced the diffusion activation energy of metal atoms in NbC0.5–MC and increased the diffusion driving force. In addition, the diffusion process of WC in NbC0.5 was analyzed. Phase transformation of WC to W2C was found during diffusion. The experiment proves that HECs may be easily prepared with the participation of the NSCs, and this work provides the theoretical basis for the alloying of covalent transition metal compounds.

Recently, high-entropy ceramics have attracted considerable attentions because of comprehensive physical and chemical properties of high hardness, fracture toughness, and conductivity. However, as a newly emerging class of materials, the synthesis, performance and applications of high-entropy ceramics are subject to further development. Here, we reported a new non-stoichiometric TiC0.4/WC/0.5Mo2C medium-entropy carbide (MEC) with a rock-salt structure. Attributed to the solid solution strengthening and twinning strengthening, the TiC0.4/WC/0.5Mo2C sintered at 1900 °C by spark plasma sintering (SPS) shows superior mechanical behaviors of microhardness (21.7 GPa), which exceeds that expected from the rule of mixture (ROM) of three individual metal carbides (19.1 GPa) and good fracture toughness (5.3 MPa m1/2). Significantly, the bulk synthesized via high-pressure and high-temperature (HPHT) sintering possesses smaller grain size and shows better comprehensive mechanical properties of microhardness (23.7 GPa) and fracture toughness (6.2 MPa m1/2). In addition, the effect of anion vacancies on the thermodynamic stability and synthesizability of TiC0.4/WC/0.5Mo2C was analyzed via quantitatively calculated entropy. Vacancies could significantly enhance the configurational entropy of mixing of the solid phase. The introduction of vacancy defects may expand synthetic path for entropy-stabilized ceramics, especially for multi-component high temperature refractory ceramics.

TiB2 doped Fe system alloys composites as a new generation of novel materials in sustainable society show the great potential in hot work tool steels usage. Compared with SKD61, the new generation materials are focused on improving both thermal conductivity and hardness. For the suppression of TiB2 decomposition and Fe2B formation, monophase BCC structured Fe-5Ti alloy powders were fabricated by mechanical allying method. The TiB2 addition with 30 vol% was selected for the control of hardness. The compacts sintered at 1323 and 1373K for 0.6 ks consisted of alpha-Fe and TiB2 with almost 30 vol%, which meant no decomposition of TiB2 occurred during sintering. The result agreed with the achievement of thermal stability of TiB2 in Fe-5Ti during spark sintering synthesis. The thermal conductivity and Vickers hardness of compacts sintered at 1323 and 1373K for 0.6 ks were 48.0W/(m.K), 684.7HV and 53.5W/(m.K), 717.5HV, respectively, which were 2.0, 1.3 and 2.2, 1.4 folds than those (24.0W/(m.K), 516.0 HV) of SKD61. In addition, the compression strength of two compacts sintered at 1323 and 1373K were measured to be 1698 and 2591 MPa, respectively. The compact sintered at higher temperature showed better mechanical properties and higher thermal conductivity due to the improvement of densification and interface bonding between Fe-5Ti and TiB2 as proved by the fracture modes in compression tests and the crack propagations in hardness tests. Hence, this work provides a new method for fabricating Fe2B free Fe-TiB2 composites by powder metallurgy with both improvement of thermal conductivity and hardness in the usage of hot work tool steels.