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The strong covalent bonds and low self-diffusion coefficients of high-entropy diboride (HEBs) and diboride-carbide (HEB-HEC) ceramics render their densification difficult, which limits their applications. Here, we used an ultra-fast high-temperature sintering technique to synthesize and densify several HEBs and HEB-HEC (containing 5–8 cations) ceramics within an isothermal duration of 1 min and a total sintering period of 6 min. All ceramics formed a single-phase or dual-phase high-entropy solid solution, and showed high density, high hardness and good fracture toughness. The rapid densification mechanisms were determined, and the preferential occupancy of metal cations in HEB and HEC phases was explained using a simplified ideal solution model. A good fracture toughness in the range of 3.6–5.4 MPa·m1/2 resulted from crack deflection or blunting and bridging of the rod-like diboride or boron-rich phase. This paper presents a simple, economical, and efficient method for the synthesis and densification of high-entropy ceramics and other advanced materials. [ABSTRACT FROM AUTHOR]

High-entropy nitride and carbonitride ceramics have received wide attention for their excellent properties such as high hardness, high melting point, and high wear resistance, but the susceptibility of nitrides to decomposition at high sintering temperatures has rendered their densification challenging. In this work, four multicomponent nitrides and five multicomponent carbonitrides (containing five to seven cations) were prepared through ultrafast high-temperature sintering. While only (Cr 1/7 Zr 1/7 Nb 1/7 Hf 1/7 Ta 1/7 Ti 1/7 V 1/7)N formed a single phase among the nitrides, all carbonitride systems formed a single-phase high-entropy solid solution with a relative density exceeding 92%. The polyanionic structure of carbonitrides is responsible for their high configurational entropy, which in turn results in their high solid solubility. Although carbonitrides showed higher hardness and modulus than nitrides with the same cations, their fracture toughness was lower. Among carbonitrides with different C/N ratios, the system with a C/N ratio of 5:5 showed the highest solid solubility and best overall mechanical properties. [ABSTRACT FROM AUTHOR]

Sintering inhomogeneities caused by hotspots are one of the factors hindering the development of flash sintering technology. Herein, to overcome this problem for a high-entropy pyrochlore-structured (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2) 2 Zr 2 O 7 ceramic (abbreviated as RE 2 Zr 2 O 7), we propose a simple strategy, namely, addition of Al 2 O 3 to the ceramic and achieved a significant effect. During flash sintering, rare earth ions in RE 2 Zr 2 O 7 reacted with Al 2 O 3 to form REAlO 3 and RE 2−x Zr 2 O 7–3x/2 , which substantially improved the sintering homogeneity. With an increase in the Al 2 O 3 content, REAlO 3 transformed into REAl 11 O 18. The crack deflection and bridging effect caused by the formation of these phases and their intrinsic high hardness and high modulus improved the mechanical properties of the composite ceramic. The use of an internal reaction to improve the electrical conductivity of a ceramic body is an economical and effective strategy to prevent hotspot formation during flash sintering. [ABSTRACT FROM AUTHOR]

Recently, high-entropy carbides have attracted great attention due to their remarkable component complexity and excellent properties. However, the high melting points and low self-diffusion coefficients of carbides lead to the difficulties in forming solid solution and sintering densification. In this work, six dense multicomponent carbides (containing 5–8 cations) were prepared by a novel ultrafast high-temperature sintering (UHS) technique within a full period of 6 min, and three of them formed a single-phase high-entropy solid solution. The solid solubility of the UHSed multicomponent carbides was highly sensitive to the compositional variation. The presence of Cr 3 C 2 liquid had significant contributions to the formation of solid solution and the densification of multicomponent carbides. All UHSed multicomponent carbides exhibited high hardness, which, unexpectedly, did not simply increase with increasing number of the components. The highest nanohardness with a value of 36.6 ± 1.5 GPa was achieved in the (Ti 1/5 Cr 1/5 Nb 1/5 Ta 1/5 V 1/5)C x high-entropy carbide. This work is expected to expedite the development of high-entropy carbides and broaden the application of UHS in the synthesis and densification of advanced ceramics. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The wettability and interfacial chemistry between high-entropy 5Ln 2 Zr 2 O 7 and Ag–Cu–Ti alloy were explored. • The anomalous temperature dependence of the wettability is related to the competitive diffusion of Ti and oxygen ions. • The rare-earth cations in the high-entropy ceramic displayed selective interfacial diffusion. • The high-entropy 5Ln 2 Zr 2 O 7 ceramic exhibited good wettability with the Ag–Cu–Ti alloy. We investigated the wetting of a high-entropy rare-earth oxide, (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2) 2 Zr 2 O 7 , by a molten 71Ag–27Cu–2Ti (in wt%) alloy using a modified sessile drop method at 1073–1273 K. The wettability shows a first increase and then decrease with increasing temperature, depending on the competition among the adsorption and diffusion of active Ti atoms towards triple line, the consumption of Ti due to interfacial reaction and the migration of oxygen from the substrate bulk to the interface. In addition, the La cations in the high-entropy substrate exhibited noticeable outward diffusion while the other rare-earth cations remained stable due to their different bonding strengths in the lattice. Despite the occurrence of interfacial reaction and selective diffusion, the substrate maintained the high-entropy structure after the reactive wetting. [ABSTRACT FROM AUTHOR]

• Nearly fully dense HEPOs were prepared by RFS at a low furnace temperature in seconds. • The RFSed-HEPOs displayed compositional uniformity at the atomic level. • The roles of electric field, rapid heating and external pressure during RFS were discussed. • The RFSed-HEPOs exhibited superior modulus, hardness and fracture toughness. Pyrochlore-type high-entropy oxides (HEOs) are usually sintered at high temperatures for a long time to achieve full density. Herein, we synthesized pyrochlore-structured (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2) 2 Zr 2 O 7 HEOs with densities up to 99 % at a furnace temperature of 1200 °C in seconds via reactive flash sintering (RFS). The resultant HEOs achieved compositional uniformity at the atomic level and exhibited superior modulus, hardness and fracture toughness compared to the counterparts prepared by conventional solid-state sintering (at 1600 °C for 6 h). The underlying mechanisms for the ultrafast densification of the RFSed-HEOs were addressed in view of the roles of electric field, rapid heating, external pressure and internal reactions. [ABSTRACT FROM AUTHOR]

Conventional ceramic sintering often requires high temperatures and hours of duration to achieve near full density. Herein, we adopted an innovative ultrafast high-temperature sintering (UHS) technique to densify several representative bulk oxides within an isothermal duration of 30 s and a total sintering period of several minutes, and revealed the relationship between ceramic structures and processing parameters. These achievements demonstrate the great potential of the UHS technique in the rapid densification of ceramics. Moreover, this flexible technique is expected to accelerate the material screening rate and facilitate the development of novel materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We developed a facile and low-cost approach to prepare lightweight and high-strength magnesium-matrix composites with a nacre-inspired laminated structure. First, lamellar Mg2B2O5 whisker (Mg2B2O5w) scaffolds with initial solid loadings of 10, 15 and 20 vol% were prepared by ice templating. The wettability between a molten AZ91D alloy and the Mg2B2O5w scaffold was greatly improved by the incorporation of nano-SiO2 sol in the aqueous slurry, making the preparation of nacre-mimetic AZ91D/Mg2B2O5w composite by way of pressureless infiltration feasible. The SiO2 content in the Mg2B2O5w scaffold has a significant effect on the processing and the microstructure and properties of the composites. The optimum SiO2 content was about 6-8 wt% of the total ceramic loading. A lower SiO2 content resulted in incomplete infiltration, while a higher content led to the formation of a large quantity of Mg2Si in the composite. The flexural strength of the composites seemed independent of the initial ceramic loading (10-20 vol%), whereas the compressive strength and elastic modulus increased considerably and the crack-growth fracture toughness decreased with increasing ceramic content. The mechanism for such variations was addressed. [ABSTRACT FROM AUTHOR]

A new two-dimensional supramolecular compound, {[Y(H[sub2]0)[sub8]](MHP)[sub2] (NO[sub3])[sub3]}[subn], was synthesized by the reaction of Y(NO[sub3])[sub3] 6H[sub2]0 with 4-methyl-6-hydroxypyrimidine (MHP) in methanol. It was characterized by single-crystal X-ray diffraction. Crystal data: triclinic, space group P-1 with a=9.908(2) A, b= 10.673(2) A, c= 12.408(3) A, *alpha;= 102.39(3)°, Β= 101.56(3)°, γ=90.31(3)°, Z=2. [ABSTRACT FROM AUTHOR]

[Display omitted] Rare-earth zirconate ceramics are conventionally sintered at high temperatures for long durations to achieve a full density. Herein, we synthesized and densified five lanthanide-group rare-earth zirconates (Ln 2 Zr 2 O 7 , Ln = La, Nd, Sm, Eu, Gd) containing different numbers of Ln cations in a high-throughput mode using a novel ultrafast high-temperature sintering technique within a cycle of 5 min, and investigated the effects of components on the structure and properties of the resultant ceramics. Under the high-throughput mode, the same sintering conditions make the analysis and comparison of the results more reasonable. The average grain size decreased while hardness and Young's modulus increased with an increase in the number of the Ln components in the zirconate ceramics. The mechanisms were ascribed to the sluggish diffusion and lattice distortion effect caused by the increase in entropy. [ABSTRACT FROM AUTHOR]

We demonstrated the feasibility of flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) and its in-situ joining with metal by applying an electric field. Herein, rapid densification of 3YSZ and its robust joining with 304 stainless-steel by using copper as a soft interlayer were achieved under a preset alternating current/direct current (AC/DC) field within only 1 min at 950 °C. Nevertheless, defects were present in the microstructures of the joints under the application of a single AC or DC field. The sintering-joining mechanisms were addressed in view of electric field-induced Joule heating and internal electrochemical reaction. Image, graphical abstract [ABSTRACT FROM AUTHOR]