High-entropy fluorite ceramics (HEOs) of the MexRE1-xO2-δ type are attracting increasing attention in high-temperature structural materials due to their excellent high-temperature stability, low thermal conductivity and unique oxygen ion conductivity. Conventional sintering (CS) of these materials typically requires temperatures exceeding 1600 ℃ and prolonged holding times, leading to high energy consumption and abnormal grain growth. Flash sintering (FS) uses electric field and Joule heating to reduce sintering temperature (<1000 ℃) and time to minutes, lowering energy, suppressing grain coarsening, and enhancing functionality. However, the comprehensive effects of process parameters on the microstructural evolution and defect dynamics of HEOs remain insufficiently understood. This study investigates the sintering behavior and microstructural evolution of MexRE1−xO2−δ ceramics under an applied electric field, revealing the densification mechanisms driven by multi-physical field coupling. The results demonstrate that under an electric field of 700 V/cm, the furnace temperature for the FS method is reduced by 561 ℃ compared to the CS method, yielding an average grain size between 1.5 and 3.0 μm. With increasing electric field strength, both the onset temperature and incubation time for FS method exhibit an overall decreasing trend. Simultaneously, electron paramagnetic resonance (EPR) spectroscopy reveals a substantial increase in oxygen vacancy concentration within the ceramic matrix following the application of the electric field. Driven by the strong electric field, intense electrochemical reduction disrupts the phase stability of the HEO matrix, leading to the preferential segregation of the LaYbO3 phase. As the electric field strength further increases, the remaining rare-earth (RE) elements undergo deep solid solution into this segregated phase to form a LaREO3−δ solid solution. This evolution ultimately triggers lattice expansion and abnormal grain growth within the HEO matrix.
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WC based cemented carbide are widely utilized in critical applications such as cutting tools and drilling tools due to their high hardness and wear resistance. However, conventional cemented carbide suffers from inherent limitations in corrosion resistance and high temperature resistance, which greatly restrict their application scenarios. The development of high-performance binders for WC-based alloys represents a crucial technological breakthrough for engineering applications of new-generation advanced cemented carbides. High-entropy alloys, with their compositional diversity, demonstrate potential as binder phases for cemented carbides owing to their capability of achieving superior property combinations. This study employs AlCoCrFeNi2.1 high-entropy alloy as the binder phase to fabricate WC-AlCoCrFeNi2.1 cemented carbide via spark plasma sintering. The investigation systematically examines the effects of sintering temperature and binder phase content on the microstructure and mechanical properties of WC-AlCoCrFeNi2.1 cemented carbide. The inhibition mechanism of AlCoCrFeNi2.1 binder phase on WC grain growth is elucidated. The main research content and conclusions are as follows.
WC-AlCoCrFeNi2.1 mixed powders with binder phase contents of 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% were fabricated by mechanical alloying. The WC-AlCoCrFeNi2.1 cemented carbide was subjected to spark plasma sintering at different temperatures to investigate the effects of sintering temperature and binder phase content on its mechanical properties and microstructure.
After sintering, XRD results revealed that the cemented carbide primarily consisted of WC and FCC phases. As the sintering temperature increased, the diffraction peak intensity of the WC phase gradually increased while its width decreased. Additionally, higher binder phase content led to stronger FCC phase diffraction peaks in the microstructure. Within the sintering temperature range of 1100 ℃ to 1200 ℃, the relative density of WC-10AlCoCrCuFeNi2.1 cemented carbide significantly improved from 95.60% to 97.58%. Further temperature increases resulted in negligible density changes. With rising sintering temperature, the grain size of WC-10AlCoCrCuFeNi2.1 cemented carbide gradually increased; however, excessively high temperatures induced abnormal grain growth As the sintering temperature increases, the hardness of the WC-10AlCoCrCuFeNi2.1 cemented carbide first rises and then declines, reaching a maximum value of 2264.61 HV1 at 1200 ℃. The fracture toughness of the carbide decreases with increasing sintering temperature, with the highest value being 10.51 MPa·m1/2 at 1200 ℃. As the binder phase content increased, the relative density of WC-AlCoCrCuFeNi2.1 cemented carbide progressively rose from 95.51% (5 wt.%) to 99.76% (20 wt.%), while the grain size gradually decreased. With the increase in binder phase content, the hardness of WC-AlCoCrCuFeNi2.1 cemented carbide first increases and then decreases, peaking at 2264.6 HV1 when the binder phase content is 10 wt.%. Before the binder phase reaches 10 wt.%, the hardness is primarily influenced by grain size, increasing as the grain size decreases. When the binder phase exceeds 10 wt.%, the content of the soft and tough phase increases, and its effect outweighs that of grain size, leading to a reduction in hardness. The fracture toughness gradually improves with the increase in binder phase (which acts as the soft and tough phase), reaching a maximum of 12.06 MPa·m1/2 at a binder phase content of 20 wt.%. The WC-AlCoCrCuFeNi2.1 cemented carbide exhibits optimal comprehensive mechanical properties at a sintering temperature of 1200 ℃ and a binder phase content of 10 wt.%. Under these conditions, the hardness is 2264.6 HV1, and the fracture toughness is 10.51 MPa·m1/2..
Synergistic enhancement of hardness and toughness in WC-HEA composites is achievable by optimizing sintering temperature and binder content. The optimal parameters (1200 ℃, 10% HEA) balance grain refinement, thermal stress mitigation, and phase distribution, providing strong foundation for developing high-performance WC-HEA cemented carbides.
(MgCoNiCuZn)O high entropy ceramics were prepared by using injection molding method with commercial oxide powders as the raw materials. Binder removal process was characterized by using thermalgravimetric analyzer. Phase composition and microstructure of the samples were characterized by using XRD, SEM and EDS. Mechanical properties of the sintered samples were also tested. It is demonstrated that dibutyl phthalate, stearic acids/paraffin wax and polyethylene/ polypropylene were degraded successively. The as-sintered samples were of single phase, with crystal structure of rock-salt (Fm-3m (225) space group). Both the particle diffusion rate and densification were rapidly increased at 1050 ℃. The highest relative density and fractured strength of the sintered compacts were 90.47% and 77.98 MPa, respectively. The high-entropy ceramic components can be manufactured by using injection molding technology.
Boride high-entropy ceramics have broad application prospects because of their excellent mechanical properties,high oxidation resistance and promising electrochemical properties. (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 high-entropy ceramics were prepared through boro/carbothermal reduction combined with spark plasma sintering technology. Phase composition and electrochemical properties of the as-sintered samples were studied. It is demonstrated that the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 high-entropy ceramic powders obtained at 1600 ℃, 1650 ℃ and 1700 ℃ and the bulk ceramics sintered at 2000 ℃ did not exhibit single hexagonal structure high-entropy phase. The as-sintered bulk had small content of second phase (Hf, Zr) B2 and (Hf, Zr) O2 distributed in between the high-entropy phase. As the reduction temperature is increased, the crystallinity of the powder is increased. The sintered (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 ceramics have a relative density of 96% and a hardness of (23.4 ± 1.2) GPa. In addition, the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 ceramics exhibited high energy storage performance and corrosion resistance. At a current density of 0.1 mA·cm-2 in 3.5 wt.% NaCl, the charge/discharge ratio capacitance can reach 50.29/44.50 F·cm-2 and the coulombic efficiency can be＞87%, satisfying the standards of the electrode material for supercapacitors.
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