Search

Using mechanically activated Mg(OH) 2 /AlO(OH) powder, we obtained nearly fully dense MgAl 2 O 4 ceramics with small grains by combining reactive cold sintering and ultrafast high-temperature sintering (UHS). During reactive cold sintering, the intermediate products, γ -Al 2 O 3 and α -Al 2 O 3 , stemming from the dehydration of AlO(OH), reacted with MgO to form nanocrystalline bulk MgAl 2 O 4 with a relative density of up to ∼65%. After the subsequent UHS process (1930 °C for 60 s), the relative density of the samples reached 97%. The sintering efficiency and the final density of the samples were substantially higher than those of conventional sintering (1500 °C/6 h). This work provides a new technical route for the efficient fabrication of dense and fine-grained spinel ceramics. [ABSTRACT FROM AUTHOR]

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]

Conventional sintering of lanthanum-chromite-based ceramics typically requires a long isothermal duration, which leads to severe loss of volatile components. In this study, we prepared dense LaCrO 3 (LCO), La 0.8 Ca 0.2 CrO 3 (LCCO), and La 0.8 (Mg 0.05 Ca 0.05 Sr 0.05 Ba 0.05)CrO 3 (4LCO) ceramics with stable single-phase structures through ultrafast high-temperature sintering (UHS), and the total sintering period was shorter than 8 min. An investigation of the effects of sintering parameters and alkaline earth (AE) metal dopants on the density showed that doping with AE metal promoted the densification of LaCrO 3 through the liquid-phase-assisted sintering mechanism. The hardness and conductivity of the ceramics were in the order of LCCO>4LCO>LCO because of the effect of lattice distortion and the relative densities of the pellets. This work presents a compositional-design-based method to obtain high-performance perovskite-type oxides, and it is expected to broaden the use of UHS for the densification of novel ceramics. [ABSTRACT FROM AUTHOR]

Unidirectional freeze casting followed by sintering and infiltration treatments has been proved to be a promising method to produce lamellar composites with good strength and toughness. However, it remains a great challenge to tailor the microstructure, particularly the lamellar orientation at the centimeter scale and the architectural features over multiple scales. Herein, we prepared Al/(Al 2 O 3 –TiC) composites with a long-range ordered lamellar architecture via bidirectional freeze-casting and melt-infiltration techniques. The incorporation of a certain amount of TiC (∼3 μm in diameter) into the Al 2 O 3 slurry increased the solidification velocity and decreased the ceramic layer thickness. Furthermore, it greatly facilitated the infiltration of liquid Al into the interlamellar channels and in-layer cavities, thus improving the mechanical properties of the composites. The maximum flexural strength (474 ± 8 MPa) and crack-growth toughness (42.7 ± 2.7 MPa m1/2) appeared in the composite containing ∼27 vol% ceramics with Al 2 O 3 :TiC = 5:5. Moreover, the composites exhibited anisotropic mechanical properties. The flexural strength loaded in the direction parallel to the ceramic layers was higher than that perpendicular to them, while the toughness exhibited an opposite trend. The main toughening mechanisms included crack blunting, crack deflection, plastic deformation of the metal layers and multiple cracking. This work offers a cost-effective and scalable method for the fabrication of laminated composites with exceptional damage tolerance. [Display omitted] • A new strategy is proposed to construct 3D-aligned lamellar hierarchical structure. • The presence of TiC facilitates the infiltration of Al into the ceramic lamellae. • Increasing TiC:Al 2 O 3 ratio reduces layer thickness and promotes multiple cracking. • Enhanced strength and toughness stem from the optimized structure and composition. [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]

• 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 constructed a nacre-inspired laminate-reticular hierarchical architecture in Cu/(TiC−Cr 3 C 2) composites by tuning the wettability between loose freeze-cast ceramic lamellae and Cu melt. This unique architecture takes full advantage of superb intrinsic strength of the ceramic particles and toughness of the metal, stimulating multiple extrinsic toughening mechanisms such as synergistic deformation of the metal and ceramic layers, ductile-ligament bridging and multi-cracking mode. As a consequence, the resultant composites containing ~30 vol% ceramics exhibited exceptional damage-tolerant properties with a fracture toughness of 62.6 ± 1.0 MPa⋅m1/2 and a bending strength of 639 ± 27 MPa. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A nacre-like magnesium matrix composite with high carbon nanotube (CNT) contents (up to 4.40 wt%) was successfully prepared under the combined effects of bidirectional freeze casting, pressureless infiltration, and hot pressing. The bidirectional freeze casting was carried out to fabricate large-scale parallelly layered CNT scaffolds. The spontaneous infiltration of an AZ91 magnesium alloy was achieved using nano-silica as the wetting promoter, and MgO and Mg 2 Si (reaction products) provided the strength of the as-synthesized composites. Furthermore, the hot pressing increased the average thickness ratio of reinforcing phase/alloy layers in the AZ91/CNT composites from 0.89 (before hot pressing) to 1.46 (after hot pressing) and also significantly improved the specific strength from 142.3 MPa/(g⋅cm−3) to 158.7 MPa/(g⋅cm−3) without sacrificing the specific toughness ((17–18) MPa⋅m1/2/(g⋅cm−3)). The resultant composites were mainly strengthened by CNTs, reaction products, and the strong interfacial bonding between CNTs and the Mg matrix. The key toughening mechanisms for the as-prepared composites were crack deflection, branching, and CNT pull-out. This study provides a new idea for the economical and efficient preparation of lightweight and damage-tolerant composites with high CNT contents. Image 1091852 [ABSTRACT FROM AUTHOR]

The wetting of (100), (110) and (111) MgAl 2 O 4 single crystals by molten Al at 1073–1273 K in vacuum was investigated using a dispensed sessile drop method to determine the effect of the substrate orientation on the wettability and reaction in this system. This system is non-wetting in nature. The initial contact angles are generally in the range of 96–106°, slightly decreasing with increasing temperature but without significant dependence on the MgAl 2 O 4 surface orientation. However, the interfacial reaction is sensitive to the MgAl 2 O 4 surface orientation and temperature. No reaction product was observed at 1073 K while the thickness of the Al 2 O 3 product layer was in the order of (100) > (110) > (111) at 1173 K and 1273 K. During the reactive wetting process, significant reconstruction and "whisker growth" occurred at the periphery of the triple line due to the stress created at the substrate surface as a result of volume change between the reactant and product, and the morphology of the "whiskers" was closely related to the MgAl 2 O 4 crystal orientation. The formation of these "whiskers" not only affected the wetting behavior but also weakened the dependence of the wettability on the MgAl 2 O 4 surface orientation. [ABSTRACT FROM AUTHOR]

Al−7Si−5Cu/Al 2 O 3 −ZrO 2 composites with nacre-like structures were prepared via ice-templating and gas pressure infiltration techniques. The composites were subsequently heat-treated at 850 °C for 0, 30, 60, 90 and 120 min to regulate the interfacial reaction between Al and ZrO 2 . The yield of larger (Al 1−m , Si m ) 3 Zr and ZrSi 2 phases increased with longer dwell times. The compressive strength initially increased and then decreased. The highest strength was observed in composites treated for 60 min and reached 1600±40, 1261±30 and 1033±22 MPa at temperatures of 20, 150 and 300 °C, respectively. These values increased by 30−40% as compared to those of the non-treated counterparts and were 2-, 5- and 12-fold more than those of the matrix alloy, respectively, which is demonstrative of the material's excellent load-bearing capacity, particularly at elevated temperatures. [ABSTRACT FROM AUTHOR]

Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al 2 O 3 −ZrO 2 composites with initial ceramic loading of 30 vol% and different Al 2 O 3 :ZrO 2 weight ratios (Al 2 O 3 :ZrO 2 =1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al 2 O 3 −ZrO 2 scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al 2 O 3 content. During pressureless infiltration, multiple chemical reactions took place between ZrO 2 and the Al−12Si−10Mg alloy and the main reaction products were (Al 1−m , Si m ) 3 Zr, Al 2 O 3 and ZrSi 2 phases. The degree of the reaction depended on the ZrO 2 content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al 2 O 3 content, but three-point bending strength showed a first decrease and then increase. When Al 2 O 3 :ZrO 2 =1:9, the compressive and bending strength of the composites reached about 997±60 MPa and 426±10 MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites. [ABSTRACT FROM AUTHOR]

Inspired by nacre, we designed biomimetic metal–ceramic composites in which hard and ductile phases were alternately arranged. We first prepared lamellar-structured TiC scaffolds with 25, 30 and 35 vol% solid loadings using a unidirectional freeze casting technique and then measured wetting and infiltration dynamics for a commercial Al cast alloy, ZL107, with the main composition of Al–7Si–5Cu on the porous TiC scaffold using a modified sessile drop method at 850 °C. The wetting was affected by liquid spreading at horizontal surface and infiltration in depth, while the latter played a dominant role in the decrease in contact angle. On the basis of the wetting results, the lamellar ZL107/TiC composites were successfully fabricated by pressure infiltration of the molten ZL107 alloy into porous TiC scaffolds and their mechanical properties were evaluated. The compressive strength and elastic modulus increased while bending strength decreased with increasing TiC content, giving maximum values of 1166 ± 20 MPa, 205 ± 2 GPa and 363 ± 5 MPa, respectively. Formation of (Al m ,Si 1 − m ) 3 Ti, Al 3 Ti and Al 4 C 3 phases in the composites was presumed to deteriorate the toughness of the composites, leading to brittle fracture under loading. [ABSTRACT FROM AUTHOR]

The strong covalent bonding of TiC renders its densification through conventional sintering difficult. Here, we propose a method involving liquid-phase-assisted ultrafast high-temperature sintering (UHS) for obtaining nearly full density of TiC ceramics by the addition of Cr 3 C 2. The samples were heated at a rate of 600 °C/min to 2200 °C and held at this temperature for 1 min. The effects of sintering parameters and the Cr 3 C 2 content on the relative density and microstructure of the sintered samples were investigated. The main causes of rapid densification were particle rearrangement associated with the Cr 3 C 2 liquid phase, dissolution-reprecipitation associated with the solid solution, and the weak evaporation of Cr formed during UHS. In particular, the addition of Cr 3 C 2 helped increase the hardness and elastic modulus of TiC significantly. This paper presents an effective and extensible method involving UHS for rapidly obtaining dense ceramics. [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]

Lightweight Al/B 4 C composites with a gradient lamellar structure were fabricated through centrifugal freezing and pressure infiltration. Their ceramic volume fraction showed a continuous increase from the central region to the surface region, the increase being from approximately 23 vol% to 44 vol%, and the spatial variation of their composition and microstructure led to a gradient change in their mechanical properties. The bending strength and hardness increased with the B 4 C content, and they attained the highest values of 424 ± 16 MPa and 130.6 ± 4.2 HV 0.3 at the surface region of the composite, respectively. By contrast, the work of fracture reached the maximum value (3763 ± 268 J/m2) at the central region of the composite because of the high metal content and the existence of multiple extrinsic toughening mechanisms. The proposed method is versatile and economical and is suitable for the preparation of composites with heterogeneous structures and gradient properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple method is proposed to construct a nacre-inspired "brick–mortar" structure. • The feature of freeze-cast scaffolds depends notably on ceramic particle size. • In-situ reaction increases the hard-phase content in composites up to 86 vol%. • The presence of "mortars" promotes multiple cracking and improves toughness. The construction of a hierarchically ordered "brick-and-mortar" structure with a high content of "brick" phase is a key challenge in the preparation of nacre-mimetic composites. Herein, inspired by the transverse cracks in the ceramic lamellae after freeze-drying caused by the secondary nucleation of ice crystals during directional freezing of water-based ceramic slurry, we propose a new idea to use these structural defects and an in-situ reaction to construct composites with a nacre-like "brick-and-mortar" structure and high hard-phase content. This uses ice-templating to first prepare lamellar TiO 2 scaffolds with transverse cracks that separated the ceramic lamellae into "brick" whose size was controlled by adjusting the initial ceramic particle size (50, 300, and 700 nm). After the reactive infiltration, these cracks were filled with molten Al, leading to the formation of a "brick-and-mortar" structure with a high hard-phase content (86 vol%). The increasing ceramic particle size reduced the hard-phase content but significantly increased the aspect ratio (height/width) of the ceramic "brick" and the fracture toughness. The excellent damage tolerance was attributed to multiple toughening mechanisms, i.e. , multiple cracking, crack deflection, and uncracked-ligament bridging of the metal layers. The existence of "mortar" increased the probability of the formation of multiple cracking. [ABSTRACT FROM AUTHOR]

Simultaneously improved impact toughness and wear resistance of high Cr tool and die steels (HCS) enable them to be widely used in the lightweight field. In this study, TiC + TiB 2 /HCS steel was prepared by pre-dispersed ceramic nanoparticles combined with specific heat treatment. The effects of ceramic nanoparticles on the microstructures, mechanical properties and wear resistance of TiC + TiB 2 /HCS steel were investigated by comparing it with shield machine tool steel (H13 steel). The results demonstrated that the introduction of ceramic nanoparticles refined the microstructure of the TiC + TiB 2 /HCS steel and uniformed the distribution of the precipitates. For TiC + TiB 2 /HCS steel and H13 steel with the equivalent hardness values, the impact toughness and the wear resistance of TiC + TiB 2 /HCS steel were 67.3 % and 39.5 % higher than that of H13 steels, respectively. Moreover, when the wear resistance was comparable, the impact toughness of TiC + TiB 2 /HCS steel was 89.1 % higher than that of H13 steel. This study provides an innovative solution to prepare high-service performing service life tools and die steels to replace shield machine tool steels. • Using pre-dispersed ceramic nanoparticles combing specific heat treatment to fabricate TiC + TiB 2 /HCS steel. • Refined matrix microstructure, finer carbides were obtained and more uniform dispersed of TiC + TiB 2 /HCS steel. • Comprehensive performance including hardness, toughness and wear resistance of TiC + TiB 2 /HCS steel was improved. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA)/magnesium (Mg) composites are a promising alternative material for bone repair in load-bearing sites. However, the poor wettability between Mg and HA as well as the extreme sensitivity of Mg to oxidation and high vapor pressure at elevated temperatures makes the preparation of HA/Mg composites rather difficult. Herein, a facile strategy for improving the wettability of HA by Mg was proposed to enable the successful preparation of bio-inspired HA/Mg composites via directional freezing and pressureless infiltration. SiO 2 nanoparticles were introduced into the freeze-cast HA scaffold by doping or soaking to promote the spontaneous infiltration of the Mg melt. The resulting HA/Mg composites displayed a delicate biomimetic lamellar structure with alternating ceramic/metal arrangements and demonstrated higher compressive strength (increased by 140%) and wear resistance (increased by 1200%) than porcine bones. In addition, the composites exhibited progressive degradation and surface apatite mineralization in a simulated body fluid environment, making them potentially promising for biomedical applications. This study provides a facile and tailorable method for the design and preparation of novel Mg-matrix composites with bio-inspired structures and biomedical functions. [ABSTRACT FROM AUTHOR]

We proposed a new strategy of combining dynamic freeze casting with pressure infiltration and successfully prepared an antler-bone-inspired gradient metal-ceramic composite. As exemplified by Al-7Si-5Cu/Al 2 O 3 , the resultant composite exhibits the unique mechanical properties of being externally hard, strong, and wear-resistant but internally soft and tough owing to its compositional and structural gradients and delicate lamellar microstructures. This study offers a feasible, flexible, and scalable approach to designing and preparing functionally gradient materials with biomimetic structural features and exceptional properties. Unlabelled Image [ABSTRACT FROM AUTHOR]

We prepared B 4 C/Al laminated composites via ice-templating and gas-aided pressure infiltration and investigated the effects of TiO 2 addition on the microstructures and mechanical properties of the composites. The incorporation of TiO 2 led to the formation of TiB 2 after sintering, reduced the formation of harmful phases and increased the strength of ceramic architectures. However, its excessive addition resulted in the cracking of ceramic layers and the formation of metal strips after Al infiltration. The bending strength, fracture toughness and work of fracture of the composites first increased and then decreased with increasing initial TiO 2 content, reaching maxima of 420 ± 20 MPa, 44 ± 2 MPa m 1/2 and 5002 ± 175 J m −2 , respectively. The specific strength and toughness are comparable to those of titanium alloys. Furthermore, fracture modes and toughening mechanisms were thoroughly addressed by analyzing crack propagation paths and fracture surface morphologies. Crack deflection and metal bridging are two primary extrinsic toughening mechanisms. [ABSTRACT FROM AUTHOR]

We prepared Al/TiC composites with different ceramic volume fractions (15, 25 and 35 vol%) using ice-templating and pressure infiltration. The thickness of the lamellar layer and the porosity in the ceramic layer of the TiC scaffolds were controlled by varying the slurry concentration. The Al/15 vol%TiC composite had a thick metal layer and a low-density ceramic layer, which effectively dissipated the stress at the crack tip and fractured in a multiple-crack-propagation mode, giving bending strength of 355±3 MPa and fracture toughness of 81±2 MPa m 1/2 . However, the Al/25 vol%TiC and Al/35 vol%TiC composites had much higher bending strength (417−500 MPa) but lower fracture toughness (46−33 MPa m 1/2 ) as compared to the Al/15 vol%TiC composite, and they fractured in a single-crack-propagation mode. In addition, an increase in the brittle TiAl 3 phase with increasing ceramic volume at the fracture surface greatly deteriorated the toughness of the Al/TiC composites. Finally, the relationship between cracking mode and structure features in the laminated composites was discussed to account for the toughening mechanism. [ABSTRACT FROM AUTHOR]

Silicate-bonded porous SiC scaffolds with lamellar structures were prepared by freeze casting and liquid-phase sintering. It was found that the viscosity and solidification velocity of SiC water-based slurries with 30 vol% solid loading decreased with increasing Al 2 O 3 –MgO (AM) addition. As the AM content increased from 10 to 30 wt%, the lamellae of the sintered scaffolds became denser and the porosity decreased from 69±0.5% to 62±0.5%, while the compressive strength improved from 25±2 to 51±2 MPa. The dynamics of pressureless infiltration for an Al–12 Si–10 Mg alloy on the SiC porous scaffold was measured and the composites with lamellar-interpenetrated structures were successfully produced. Both the compressive strength and the elastic modulus of the composites increased with increasing AM content. The maximum strength reached 952±24 MPa and the highest elastic modulus about 156 GPa, respectively, in a longitudinal direction, increasing about 32% and 11% as compared with those of the composites without AM. [ABSTRACT FROM AUTHOR]

We prepared a large-scale aligned structure in Al 2 O 3 porous ceramics by a simple and novel bidirectional freeze-casting technique. This technique uses a side metal plate to achieve cold-surface cooling from the bottom to generate dual temperature gradients to control the nucleation and growth of ice crystals. By recording the slurry temperature in situ, we obtained various temperature gradients for the samples prepared by this technique using 3 mm thick copper, aluminium and stainless-steel plates as the cold surfaces. The architectures of the scaffolds produced under these freezing conditions were investigated to determine the effect of the temperature gradients on the morphology of the microstructure. Finally, a model was proposed to account for the temperature gradient regulatory mechanism of the transition from a dendritic structure to a parallel structure. [ABSTRACT FROM AUTHOR]

The application of a direct current, regardless of its polarity, can significantly improve the wettability of ZrO 2 –8 mol% Y 2 O 3 (YSZ) by molten Cu at 1373 K, and this effect was more pronounced when YSZ was connected to cathode. The mechanisms for the wetting improvement varied with the change in the current polarity. When YSZ was connected to the cathode, the oxygen ions in the YSZ body driven by the external electric power moved to the solid–liquid interface and dissolved into liquid Cu, forming O Cu clusters. As a consequence, the solid–liquid interfacial energy and liquid surface tension were greatly reduced and wettability improved. On the other hand, when YSZ was connected to anode, the improvement in the wettability was mainly driven by the formation of nonstoichiometric zirconia and metallic Zr at the interface. Nevertheless, the newly formed ZrO 2 at the triple line region inhibited further spreading of liquid front. [ABSTRACT FROM AUTHOR]

Novel bio-inspired ZL205A/SiC composites with a lamellar-interpenetrated structure were successfully fabricated via gas-pressure infiltration of a commercial ZL205A alloy into freeze-cast porous SiC scaffolds. The influences of initial ceramic content (20, 30 and 40 vol%) on the microstructure and damage-tolerance behavior of the resultant composites as well as their toughening mechanism were investigated. With an increase in the ceramic content in the composite, the flexural strength and fracture toughness in the longitudinal direction gradually decreased; whereas, in the transverse direction they showed a first increase and then decrease but their elastic modulus increased. The composites displayed significant damage-tolerance anisotropy, with higher strength and toughness in the longitudinal direction (parallel to the lamellae) than that in the transverse direction (perpendicular to the lamellae). In the longitudinal bending, the ZL205A/20 vol%SiC composite exhibited the maximum flexural strength (760 MPa) and the largest fracture toughness (33.0 MPa m 1/2 ). The excellent damage tolerance of the composites was attributed to multiple toughening mechanisms such as plastic deformation in the matrix alloy, crack blunting, deflection and branching, and uncracked-ligament bridging of the ductile alloy layers. However, in the transverse bending, the crack propagated along the ceramic layer in the composites and thus greatly weakened their damage-tolerance capability. [ABSTRACT FROM AUTHOR]

We report a novel strategy for rapid joining of yttria-doped ZrO 2 and Ni at 1373 K in a vacuum without using any brazing filler or other types of interlayer. Electrochemically-driven diffusion bonding was established at the Ni–ZrO 2 interface by applying an external electric power, and the interfacial chemistry was readily manipulated by altering the current polarity and intensity. The underlying mechanisms were addressed based on the considerations of current-induced oxygen ion movement and atomic diffusion and reaction. [ABSTRACT FROM AUTHOR]

We put forward a novel technique to improve the wettability of ZrO 2 –3 mol%Y 2 O 3 (PSZ) substrate by molten Al at 973 K. When the PSZ substrate and the Al drop were respectively connected to anode and cathode, the wetting between them was greatly improved by applying a minor current. The mechanisms were ascribed to the disruption of the oxide film covering the Al drop, the formation of substoichiometric ZrO 2 − x and the release and adsorption of metallic Zr atoms at the interface; while the formation of a ZrAl 3 phase at the interface plays a limited role. [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]