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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]

Magnesium matrix composites are essential lightweight metal matrix composites, following aluminum matrix composites, with outstanding application prospects in automotive, aerospace lightweight and biomedical materials because of their high specific strength, low density and specific stiffness, good casting performance and rich resources. However, the inherent low plasticity and poor fatigue resistance of magnesium hamper its further application to a certain extent. Many researchers have tried many strengthening methods to improve the properties of magnesium alloys, while the relationship between wear resistance and plasticity still needs to be further improved. The nanoparticles added exhibit a good strengthening effect, especially the ceramic nanoparticles. Nanoparticle-reinforced magnesium matrix composites not only exhibit a high impact toughness, but also maintain the high strength and wear resistance of ceramic materials, effectively balancing the restriction between the strength and toughness. Therefore, this work aims to provide a review of the state of the art of research on the matrix, reinforcement, design, properties and potential applications of nano-reinforced phase-reinforced magnesium matrix composites (especially ceramic nanoparticle-reinforced ones). The conventional and potential matrices for the fabrication of magnesium matrix composites are introduced. The classification and influence of ceramic reinforcements are assessed, and the factors influencing interface bonding strength between reinforcements and matrix, regulation and design, performance and application are analyzed. Finally, the scope of future research in this field is discussed. [ABSTRACT FROM AUTHOR]

Since the aluminum matrix composites prepared by additive manufacturing are prone to defects such as pores and cracks, the properties of the formed composites cannot be further improved. Therefore, the preparation of SiC/AlSi10Mg composites with high modulus and high strength by selective laser melting technology is of great significance for the wide application of aluminum matrix composites. This work will further investigate the defect formation, microstructure evolution, and solidification mechanism of the composites. The matrix microstructure of the composites can be efficiently refined by adding SiC. In addition, the 5 wt.% SiC/AlSi10Mg composites showed improvements in the tensile yield strength, microhardness, bending strength, elastic modulus, and ultimate tensile strength as compared to the AlSi10Mg alloy. These increases were 21.1 %, 18 %, 8.7 %, 23.2 % and 9.2 % respectively. The strengthening mechanisms at room temperature include fine grain strengthening, thermal mismatch strengthening, solid solution strengthening and precipitation strengthening. It is also mentioned that the primary causes of the decrease in toughness are stress concentration and the existence of the brittle precipitation phase (Al 4 C 3). The increase in high-temperature strength is attributed to the pinning role of SiC and precipitate phases relative to grain boundary and dislocation climbing. [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]

In the general environment of lightweight automobiles, the integrated die-casting technology proposed by Tesla has become the general mode to better achieve weight reduction in automobiles. The die-casting mold required by integrated die-casting technology has the characteristics of large scale and complexity. Hence, higher requirements are put forward for the comprehensive performance of the die steel. Despite the stagnation in the progress of conventional strengthening methods, enhancing the performance of die steel has become increasingly challenging. Indeed, it necessitates exploring novel die steel and optimizing heat treatment and reinforcement technologies. This article summarizes and analyzes the development status of die steel and corresponding heat treatment and microstructure manipulation as well as strengthening methods and elaborates on an excellent nano-strengthening technology. Furthermore, this review will aid researchers in establishing a comprehensive understanding of the development status of die steel and the processes utilized for its strengthening. It will also assist them in developing die steel with improved comprehensive performance to meet the high demand for mold steel in the integrated die-casting technology of the new era. [ABSTRACT FROM AUTHOR]

It is well known that the development of lightweight alloys with improved comprehensive performance and application value are the future development directions for the ultra-high-strength 7xxx series Al-Zn-Mg-Cu alloys used in the aircraft field. As the lightest metal element in nature, lithium (Li) has outstanding advantages in reducing the density and increasing the elastic modulus in aluminum alloys, so Al-Zn-Mg-Cu alloys containing Li have gained widespread attention. Furthermore, since the Al-Zn-Mg-Cu alloy is usually strengthened by aging treatment, it is crucial to understand how Li addition affects its aging precipitation process. As such, in this article, the effects and mechanism of Li on the aging precipitation behavior and the impact of Li content on the aging precipitation phase of Al-Zn-Mg-Cu alloys are briefly reviewed, and the influence of Li on the service properties, including mechanical properties, wear resistance, and fatigue resistance, of Al-Zn-Mg-Cu alloys are explained. In addition, the corresponding development prospects and challenges of the Al-Zn-Mg-Cu-Li alloy are also proposed. This review is helpful to further understand the role of Li in Al-Zn-Mg-Cu alloys and provides a reference for the development of high-strength aluminum alloys containing Li with good comprehensive properties. [ABSTRACT FROM AUTHOR]

Nacre-inspired laminated composites have been proven to possess a unique combination of strength and toughness. In this study, we fabricated nacre-mimetic Cu/TiC composites via unidirectional freezing of aqueous TiC slurries containing different amounts of NiO additives, followed by ice sublimation, carbothermal reduction of NiO to Ni during sintering and then gas-pressure infiltration of the Cu melt. The introduction of Ni greatly facilitated the densification of ceramic lamellae and enhanced the interfacial bonding between Cu and TiC. The resultant composites displayed outstanding damage tolerance and anisotropic electrical conductivities. Specifically, for an ∼31 vol% TiC–Cu composite containing 24 wt% Ni in the ceramic lamellae (based on the TiC content), a fracture toughness (K Jc) of 72.5 ± 1.0 MPa·m1/2, work of fracture of 53.4 ± 3.5 kJ/m2, bending strength of 725 ± 11 MPa and longitudinal electrical conductivity of 22.7 MS/m (∼60% of the Cu matrix) were achieved, which were approx. 81%, 536%, 122% and 97% higher than those of the Ni-free composite, respectively. Noticeable toughening was demonstrated to be a consequence of multiple cracking, plastic deformation and uncracked-ligament bridging of the metal layers, as well as crack deflection and blunting. On the other hand, significant strengthening resulted from tailoring the microstructures in the ceramic layers and at the Cu/TiC interface as a result of Ni doping. We believe that the facile strategy adopted herein provides an effective way to solve the problems of wetting and bonding related to metal infiltration and can be readily extended to the preparation of other nacre-inspired metal−ceramic composites. [ABSTRACT FROM AUTHOR]

Directionally aligned prismatic and lamellar porous alumina scaffolds with a high strength-to-density ratio were fabricated from submicron Al2O3 powders and a tiny quantity of nanoscale TiO2 sintering aids by freeze casting using TBA and water as solvents. Both freezing temperature (− 10 °C, − 50 °C, − 90 °C) and sintering temperature (1300 °C, 1350 °C, 1400 °C) were varied to adjust pore parameters while a low solid loading (15 vol%) was maintained to ensure high porosity. This paper describes and compares the microstructures, porosity, pore size, wall thickness and compressive behavior of the scaffolds with two typical pore morphologies (lamella and honeycomb), which help to identify their scope of application and to unveil the relationship between pore morphology and mechanical property to optimize the material performance. The failure modes of these two types of scaffolds under compression were simulated. The TBA-based 1 wt% TiO2-containing alumina scaffolds with dense ceramic walls that were freeze-cast at − 90 °C and sintered at 1400 °C exhibited a compressive strength of 160 MPa with a porosity of 59%, indicating lightweight and high-strength characteristics. [ABSTRACT FROM AUTHOR]

Simultaneously improving the wear resistance and toughness can extend the service life of steel. In this study, nano-TiC-H13 steel was successfully fabricated by pre-dispersion nano-TiC/Al master alloy in conventional casting to simultaneously improve the wear resistance and toughness. The influence of nano-TiC ceramic particles on the microstructure, tensile properties, impact toughness, and wear behavior under the synergistic effect of high load and temperature was explored. Results indicated that nano-TiC ceramic particles can effectively refine the microstructure and promote the precipitation of the finer carbides, which significantly improved the properties of steel. The no-notch impact toughness (380.2 J/cm2), U-shaped notch impact toughness (36.6 J/cm2), and yield strength (1440 MPa) of nano-TiC-H13 increased by 12.7%, 31.2%, and 8.2%, respectively, compared with that of H13. Furthermore, the volumetric wear rate (8.2 × 10−10 m3/m) of nano-TiC-H13 under 450 °C and 30 N is decreased by 28.6% in contrast with H13. The high strength and plasticity in nano-TiC-H13 can resist the intrusion of debris and reduce plastic deformation. This work provides an innovative approach for the simultaneous improvement of the wear resistance and toughness of steel. • Nano-TiC refines the microstructure and promotes the finer precipitates distributed. • Finer microstructure inhibits stress concentration and improves strength and toughness. • Higher strength resists debris intrusion, resulting in wear resistance improvement. • Excellent toughness retards crack extension and delays failure of steel. [ABSTRACT FROM AUTHOR]

The size, distribution, and morphology of TiC particle in Fe–Ti–C system have a great influence on the mechanical properties of TiC/Fe composites. In this work, TiC/Fe composites were fabricated in the Fe–Ti–C system with different carbon source and molar ratio by combustion synthesis and hot-pressing method. Morphology and size of ceramic particles, as well as microstructure, interface bonding and mechanical properties of composites were compared. The results showed that the size of TiC particles decreased with increase of Fe content of Fe–Ti–C systems fabricated by the same carbon source, while the particles change from spherical shapes to cubic shapes which can reduce stress concentration between ceramic particles and matrix. Furthermore, TiC/Fe composites fabricated by 5Fe–Ti-carbon blacks (CBs) system exhibited superior yield strength (1523 MPa) compressive strength (2203 MPa) and microhardness (691.5 HV), caused by the high interface bonding strength and lamellar pearlite matrix which can commendably limit the dislocation slip. By comparison, TiC/Fe composites fabricated by 21Fe–Ti-carbon nanotubes (CNTs) system showed higher fracture strain (25.85%) on account of the ferrite matrix with favorable plastic. This work reveals the influence of carbon source and molar ratio of Fe–Ti–C system on TiC/Fe composites, which is helpful to further improve the properties of TiC/Fe composites. [ABSTRACT FROM AUTHOR]

Thermal fatigue failure is one of the main factors affecting the service life of hot work die steel. Achieving excellent thermal fatigue resistance for hot working die steels can benefit the industry economically. In this work, (TiC + TiB 2)/Al master alloys were used to add TiC–TiB 2 nanoparticles into high-Cr die steels, which achieves microstructure manipulation and obtains excellent thermal fatigue resistance and strength-plastic combination. The results showed that after being manipulated by 0.02 wt% TiC–TiB 2 nanoparticles, the surface oxidation zone of the high-Cr die steel after different thermal fatigue cycles is reduced than high-Cr die steel without manipulation. TiC–TiB 2 nanoparticles effectively refined the heat-treated microstructure of high-Cr die steel, promoting the Cr element and alloy carbides being more uniformly distributed in the matrix, which prevents the occurrence of oxidative pitting and conducive to the formation of a dense and uniform Cr 2 O 3 oxide layer, and further preventing the initiation of thermal fatigue cracks. Moreover, these finer and more uniformly distributed precipitates in TiC–TiB 2 nanoparticles manipulated high-Cr die steels will promote stress dispersion and hinder thermal fatigue crack propagation. This work provides a promising avenue for the design of low-cost, high-performance, and long-life die steels for industrial applications. • The microstructure has been manipulated with traces TiC–TiB 2. • Thermal fatigue cracks initiation are closely correlated to surface oxidative erosion. • Nanoparticle-reinforced steels have better thermal fatigue resistance. [ABSTRACT FROM AUTHOR]

Lightweight NiAl alloys are expected to replace high-density nickel-based superalloys, but their mechanical performance needs to be improved. In this work, NiAl–30Cr composites with a novel heterogeneous microstructure composed of fine NiAl matrix and Cr single-phase was successfully prepared. Nanoscale Cr particles with 15 nm in size precipitated in NiAl matrix are coherent with NiAl matrix owing to very low interplanar and interatomic spacing mismatch. Such a composite microstructure makes NiAl–30Cr exhibit high strength and high toughness. The yield strength (1207 MPa), ultimate compressive strength (2307 MPa), product of strength and plasticity (29.3 GPa%), and fracture toughness (10.76 MPa m1/2) of NiAl–30Cr increased by 96.6%, 85.6%, 55.1% and 19.7% respectively at room temperature compared to the corresponding ones of NiAl. At 1000 °C, the yield strength (144 MPa) of NiAl–30Cr was 85.9% higher than that of NiAl. Solution strengthening and precipitation strengthening were the key strengthening mechanisms at room temperature. The enhancement in toughness was attributed to grain refinement, increased crack propagation paths, weakened Ni–Al covalent bonding and coordinated deformation of Cr single-phase and NiAl matrix. By contrast, the main strengthening mechanism at 1000 °C is the solid solution Cr atoms hindering dislocation climbing and the stable interface bonding between the Cr nanoprecipitation phase and the NiAl matrix. This work provides new ideas for preparing high-strength and tough NiAl alloy. • NiAl–30Cr consists of NiAl and Cr single-phase, which can coordinate deformation. • Coherent Cr nano-precipitates distribute in NiAl matrix, and interface is stable. • The yield strength increased by 96.6% and 85.9% at 25 °C and 1000 °C. • The strengthening and toughening mechanisms are revealed. [ABSTRACT FROM AUTHOR]

Fatigue resistance under extreme stress conditions is an important indicator to evaluate industrial application potential of Al-Si-Mg alloys, but their fatigue resistance is inherently weakened by large grain size, long-needle Si phases and coarse precipitates. This work reports significantly optimized microstructure configuration and fatigue resistance of hypoeutectic Al-Si composite optimized by the nanocrystallization products of a NiNbTi metallic glass. It was proved the in-situ NiTi (B2) nanocrystals can serve as the heterogeneous nucleation sites of α-Al and β-Mg 2 Si and the growth retarder of eutectic Si. Particularly, the optimized composite exhibited nearly 5 times and 6 times longer fatigue life than the unoptimized alloy at 120 MPa (60 Hz) and 240 MPa (20 Hz), respectively. The fatigue strength (N = 107) was increased by 21.7 % and 25.9 % at 60 Hz and 20 Hz, respectively. The α-Al refinement enhanced the resistance to fatigue crack initiation. The refinement and spheroidization of eutectic Si phases reduced stress concentration. Also, the austenite-martensite phase transformation of NiTi afforded more energy for precipitation. Refined β-Mg 2 Si and β'' phases were facilitated to interact with dislocations, improving the resistance to dislocation slip during cyclic strain through the dislocation shearing effect. This work provides a theoretical basis for the future development of Al-Si alloys and composites with excellent fatigue resistance for expanding their industrial application scope. [Display omitted] • The microstructure was fully manipulated by trace in-situ nanocrystals. • The σ b , ε l , a k , and U T were improved by 20.4 %, 29.1 %, 13.3 % and 58.7 %. • The mean fatigue strengths were 21.7 % (60 Hz) and 25.9 % (20 Hz) improved. • Refined α-Al, eutectic Si and precipitates enhanced fatigue life. [ABSTRACT FROM AUTHOR]

TiC/Al–Cu nanocomposites were fabricated in Al–Ti–C powder systems using carbon black, a mixture of C and carbon nanotubes (C + CNTs), and CNTs via an in-situ method involving combustion synthesis and hot pressing. As the carbon source changed from pure carbon black to the C + CNT mixture and pure CNTs, the size of the TiC nanoparticles decreased gradually. The nanocomposites synthesized based on the C + CNT mixture exhibited the most uniform dispersion of TiC nanoparticles. The 30 vol% TiC/Al–Cu nanocomposite prepared from the C + CNT mixture had the best comprehensive mechanical properties (yield strength (411 MPa), compressive strength (712 MPa), fracture strain (17.2%), hardness (206.8 HV), and wear resistance under the experimental conditions due to having the most uniformly dispersed TiC nanoparticles. The wear mechanism was a combination of plastic deformation, abrasion, and adhesion. This method may be a low-cost and convenient means to control the sizes of in-situ TiC nanoparticles and prepare high-performance TiC/Al–Cu nanocomposites. [ABSTRACT FROM AUTHOR]

Titanium carbide (TiC) nanoparticles with well‐designed exposed crystal planes perform intriguing prospects for functional and engineering applications. In this study, a simple and controllable in situ synthesis strategy was proposed for the synthesis of TiC nanoparticles with specific morphology. Reaction behaviors suggested that most of TiC nanoparticles were formed by an instantaneous reaction between Al3Ti and Al4C3 in the Al‐rich melt and the resultant morphology was controlled by the discrepant growing rates of (100) and (111) crystal planes. In addition, a growth morphology control model was presented for the prediction and manipulation of the morphology of TiC nanoparticles by the doping of different alloying elements Me (Me = Cu, Mg, Mn, Zn, and Si). According to the morphological observations and density functional theory analyses including the interface energy, charge density differences, and orbital hybridization: Cu, Mg, and Zn atoms could stabilize the Al/TiC(111) interface, whereas Mn and Si atoms promoted the rapid growing and disappearance of the TiC(111) planes in the Al melt. This work provides a feasible way to intelligently design and manipulate TiC nanoparticles with desirable exposed crystal planes, and exhibits a promising prospect for personalized applications. [ABSTRACT FROM AUTHOR]

The cast aluminum alloys with light weight and good castability show great potential in aerospace and automotive applications. Due to their poor weldability and the low strength of welded joints, these alloys are difficult to fuse using conventional fusion welding techniques. Here, through friction stir welding (FSW) for cast Al-Si 7 -Cu 4 -Mg 0.3 alloy manipulated by in-situ nanocrystals, a novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed, along with the guarantee of high strength-plasticity combination of the joints. The microstructure of cast Al-Si 7 -Cu 4 -Mg 0.3 alloy comprehensively manipulated by in-situ nanocrystals ensured the complete globalization of eutectic silicon and comprehensive mechanical performances of base materials to fulfill FSW. The microstructure evolution across various welded regions of the joints was revealed. The dendritic grains with a certain degree of coarsening and short needle-like eutectic silicon were formed in the heat affected zone (HAZ), and the mechanism of microstructure evolution was mainly dynamic recovery (DRV). The dynamic recrystallization (DRX) of grains in the nugget zone (NZ) resulted in regular fine equiaxed grains, and nearly spherical eutectic silicon distributed uniformly in the matrix. The optimal yield strength (YS) and ultimate tensile strength (UTS) of friction stir welded joints were 280 MPa and 400 MPa, which achieved 84.8% and 83.3% of the base material respectively (330 MPa and 480 MPa). This study contributes to producing friction stir joint of cast aluminum alloys with complex structures, as an alternative to traditional stamping-welding process of deformed aluminum alloys. Keywords • A novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed. • The overall microstructure of base materials was refined by in-situ nanocrystals. • The microstructure evolution behavior of friction stir joints in different regions was revealed. • The friction stir joints exhibited excellent strength-plasticity combination. [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]

Electrically actuated movement of liquid metals is quite promising in mechanical engineering and applied physics. However, little work has so far been performed on the effect of current polarity on the actuation of the eutectic gallium–indium (EGaIn) alloy moving on metal substrates. In this work, the spreading of EGaIn on copper (Cu) substrate under different direct-current (DC) polarities in the 0.5 mol/L NaOH solution was investigated, and the underlying mechanisms were addressed. When the Cu substrate was connected to cathode, the wetting was essentially attributed to the reduction in the oxidized surface of the Cu substrate; whereas, under the opposite polarity, the spreading was related to the tension gradient along the EGaIn–solution interface, which induced Marangoni flow, despite the fact that the EGaIn–Cu system was non-wetting in this case. Unlabelled Image • Application of DC drives the spreading of EGaIn on Cu substrate. • The spreading behavior varies greatly with DC polarity. • Spreading under wetting condition is primarily attributed to deoxidation of Cu surface. • Spreading under non-wetting condition is mainly due to Marangoni flow. [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]

Abstract Relatively high strength and good ductility are rarely obtained simultaneously in aluminum matrix composites. In the present work, dual-phased TiC n -Al 3 Ti m (n: nanosized TiC particles and m: micron-sized Al 3 Ti particles) particles were in situ synthesized in an Al-Ti-C system via the combustion synthesis method. Subsequently, (TiC n -Al 3 Ti m)/Al hybrid composites were readily fabricated at high addition levels (0, 1, 3, 5 and 7 vol%) via the re-melting and diluting method assisted ultrasonic vibration. Then, the isolated influences of the dual-phased TiC n -Al 3 Ti m particles on the solidification behaviors, microstructure evolution and mechanical properties, at both ambient- and elevated-temperatures, of aluminum alloys were systematically investigated. The experimental results revealed that the α-Al dendrites were substantially refined with a reduction of up to 4 times when compared with that of the unreinforced base alloy. Furthermore, at ambient temperature, 5 vol% (TiC n -Al 3 Ti m)/Al exhibited the optimum comprehensive mechanical properties, and the yield and ultimate tensile strength were 124.3% and 165.2% higher than those of the unreinforced base alloy, whilst the fracture strain was not sacrificed. Theoretical calculations suggest that thermal-mismatch and Orowan strengthening effects contributed most to the yield strength increment, whereas the favourable fracture strain was achieved mainly due to grain refinement. Moreover, at elevated temperature (453 K), the yield strength and ultimate tensile strength were improved by 327.8% and 236.1%, respectively, whilst the fracture strain was still at a relatively high level of 29.2%. The improved thermal resistance primarily resulted from the pinning effects of the TiC n -Al 3 Ti m particles on the grain boundaries and dislocations. Highlights • Novel dual-phased TiC n -Al 3 Ti m particles were in situ synthesized. • TiC n -Al 3 Ti m exerted refinement by heterogeneous nucleation and inhibited growth. • TiC n -Al 3 Ti m enhanced strength at 298 K by thermal mismatch and Orowan effects. • TiC n -Al 3 Ti m enhanced strength at 453 K by pinning and retarding effects. [ABSTRACT FROM AUTHOR]

Abstract The effects of current polarity, temperature and current intensity on the wettability of 3 mol% yttria-partially stabilized zirconia (3Y-PSZ) by molten 72Ag–28Cu were investigated using a direct current (DC)-coupled sessile drop method. The wettability was significantly improved with the assistance of a DC, especially when 3Y-PSZ was connected to anode. Noticeably, the contact angle rapidly decreased from 143° to smaller than 20° when the current intensity was larger than +10 mA. The wettability also showed abnormal dependence on temperature, presumably due to the competition between nucleation and growth of the m (AgCu 4 Zr) phase at the interface. The mechanisms for the significant improvement in the wettability under the DC application were ascribed to the formation of substoichiometric ZrO 2- δ , the release and adsorption of metallic Zr, and the formation of wettable m (AgCu 4 Zr) phase at the interface. The DC-assisted wetting provides a new strategy for the rapid and robust joining of 3Y-PSZ to metals. [ABSTRACT FROM AUTHOR]

Abstract The present work revealed a potential to control the static recrystallization kinetics through regulating the feature of pre-existing Mg 17 Al 12 particles in Mg-Al-Zn alloys. The AZ31 (Mg-3Al-1Zn) with rarely dispersoids exhibits the fastest recrystallization rate, while the AZ61 (Mg-6Al-1Zn) with only fine particles (∼100 nm) recrystallizes slower than AZ91 (Mg-9Al-1Zn) containing Mg 17 Al 12 precipitates with scattered size distribution (ranging from less than 100 nm to above 0.6 μm). Especially, we found that coarse Mg 17 Al 12 particles in AZ91 are easier to trigger particle stimulated nucleation (PSN) at 275 °C than 175 °C, which compensates the strong recrystallization inhibition of fine dispersoids, leading to the recrystallization dramatically transforms from retarded to accelerated. Graphical abstract Image 1 Highlights • The precipitate feature notably affects the kinetics of static recrystallization. • Recrystallization of alloys with mixed particle size is sensitive to temperature. • Coarse particles in Mg-9Al-1Zn accelerate recrystallization at high temperature. • The study shows an efficient route to control the static recrystallization process. [ABSTRACT FROM AUTHOR]

Freeze casting has been widely used in the preparation of nacre-inspired composites because of its prominent advantages in controlling the fine structure of ceramic scaffolds. However, the ceramic-phase content in composites prepared by this method is much lower than that in nacre due to the limitations of the dispersion and viscosity of the ceramic slurry. In this work, we combined the ideas of freeze casting and in-situ reaction to prepare nacre-inspired lamellar composites with high hard-phase contents. We first prepared the TiO 2 -−SiO 2 porous scaffold with an initial solid loading of 20 vol% via unidirectional freeze casting and then infiltrated it with a 6061Al alloy. During the reaction process, the TiO 2 -SiO 2 layers were progressively transformed into Al 2 O 3 layers, and the Al layers were transformed into Al 3 Ti. Composites with different hard-phase volume fractions (approx. 29%, 38%, 52% and 65%) and different interfacial bonding strengths could be obtained by altering the infiltration temperature. Increases in the hard-phase content and the interfacial bonding strength substantially enhanced the bending and compressive strengths of the composites, with maximum values of 350 MPa and 854 MPa, respectively, achieved in the composites with approx. 65 vol% hard phases. However, the highest fracture toughness of 42.9 MPa m1/2 and maximum fracture work of 3.6 kJ/m2 appeared when the hard-phase content in the composite was approx. 38 vol%, sharing an appropriate interfacial bonding strength. A robust interface favors stress transfer but impedes crack deflection, while a weak interface fails to bear loads, even though it is conducive to crack deflection. A moderately-strong interface together with a considerable amount of layered soft phase contributes to the generation of multiple-cracking, and thereby greatly toughens the metal−ceramic composite. [ABSTRACT FROM AUTHOR]

Abstract A novel Mg-8Al-2Sn-1Zn alloy with a bimodal structure prepared by hard-pate-rolling (HPR) exhibits both higher tensile strength and ductility than its fine-grained counterparts prepared by conventional rolling. By delicate electron back-scatter diffraction (EBSD) analysis, we found fine grains with weak basal texture is beneficial for basal slip and favors initial deformation. Meanwhile, coarse grains with a strong basal texture could accommodate abundant newly generated dislocations, promoting work hardening after fine grains are saturated with dislocations. For the first time, individual roles of fine and coarse grains and their synergy effect on enhancing ductility in bimodal structured Mg alloys is clarified. Graphical abstract Image 1 Highlights • A bimodal grain-structured Mg alloy is fabricated by hard-pate-rolling. • The bimodal sample has higher strength and ductility than fine-grained samples. • The synergy effect of fine and coarse grains on enhancing ductility is clarified. [ABSTRACT FROM AUTHOR]

Abstract Al–Si–Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al–Si–Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on α-Al (from 1675 µm to 199 µm) and Mg 2 Si in the inoculated Al–Si–Mg alloys. The morphology of the eutectic Si in the inoculated Al–Si–Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 µm to 11.89 µm) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe 2 B and Fe 3 Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg 2 Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity. Graphical abstract fx1 Highlights • The inoculated Al–7Si–0.3Mg alloy appeared as 199 µm fine grains. • The inoculated alloy reached 226 MPa, 343 MPa, 18.4%(δ) and 16.7%(ε f). • This work achieved the refinement of α-Al and Mg 2 Si and the spheroidization of eutectic Si. • The Fe 2 B, Fe 3 Si had better lattice mismatch with α-Al and eutectic Si. [ABSTRACT FROM AUTHOR]

Abstract The strength and toughness of a material are generally two mutually exclusive properties. Optimization of these properties can be realized by regulating microstructures based on a bio-inspired idea. Herein, we used gelatin as a pore-regulating agent to investigate the effect of microstructural transition from "nacre-like" lamellae to "honeycomb-like" reticulae on the mechanical properties of metal–ceramic composites. By introducing different quantities of gelatin into SiC slurries during freeze casting and infiltrating the sintered SiC scaffolds with pure molten Al, we prepared the Al/SiC (88/12 in volume) composites with variable yet controllable microstructures and further demonstrated that the desired properties could be achieved by tailoring their microstructures. Specifically, the Al/SiC composites with a fully laminated structure exhibited optimal fracture toughness (K Jc) of 51.9 ± 2.9 MPa m1/2 while those with a three-dimensional reticular structure displayed peak three-point flexural strength of 371 ± 6 MPa. The relationship between the microstructures and mechanical properties of the composites was addressed based on material strengthening and toughening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract In situ TiC p /Al-Cu-Mg-Si nanocomposites were prepared in Al-Ti-C systems with different carbon sources (pure carbon black, mixed carbon source (50 wt% CNTs + 50 wt% carbon black) and pure CNTs) via a combination of the combustion synthesis, hot press and hot extrusion methods. The in situ TiC p /Al-Cu-Mg-Si nanocomposites synthesized by the mixed carbon source obtained the most uniform distribution of nanosized TiC p , highest yield strength (σ 0.2) and tensile strength (σ UTS) and best fracture strain (ε f). The 30 vol% TiC p /Al-Cu-Mg-Si nanocomposite synthesized by the mixed carbon source showed superior σ 0.2 (217 MPa), σ UTS (251 MPa), and ε f (17.7%) at 533 K, which were respectively 4.3%, 4.1% and 136% higher than those of the nanocomposite synthesized by pure C black (208 MPa, 241 MPa and 7.5%) and respectively 3.8%, 1.6% and 88.3% higher than those of the nanocomposite synthesized by pure CNTs (209 MPa, 247 MPa and 9.4%). The superior high-temperature tensile strength and ductility of the nanocomposites prepared by the mixed carbon source were attributed to the homogeneous distribution of nanosized TiC p. The strengthening of the nanosized TiC p and θ′ precipitates was the main strengthening mechanism of the in situ TiC p /Al-Cu-Mg-Si nanocomposites at high temperatures. Highlights • In situ TiC p /Al nanocomposites are prepared in Al-Ti-C systems with various carbon sources. • Nanocomposites prepared by mixed C/CNTs show the best dispersion of nanosized TiC p. • Nanocomposites prepared by mixed C/CNTs show the best strength and ductility at 493 K and 533 K. [ABSTRACT FROM AUTHOR]

Abstract The effects of a small addition of nanosized TiC particles (TiC p) on the microstructure evolution of the Al-Mg-Si (6061) alloy throughout the entire fabrication process including casting, cold rolling and heat treatments were investigated. TiC p impeded the recrystallization and grain growth, refined the grain structure, and evidently increased the tensile strength without obvious decrease on ductility. The ultimate tensile strength and yield strength of the 1.0 wt% TiC p /6061 composite were 330 MPa and 275 MPa in T6 state and 438 MPa and 426 MPa in the as-rolled state, an increase of 42 MPa and 38 MPa, 41 MPa and 52 MPa, respectively, compared to the matrix 6061 alloy. The strength increase is attributed to strengthening effect of TiC p , dislocation accumulation and precipitate strengthening. [ABSTRACT FROM AUTHOR]

Abstract Zr and Sb are simultaneously added to refine and modify primary Mg 2 Si in Al–20Mg 2 Si alloys. Compared with single addition of Zr or Sb, the combined addition of Zr and Sb can result in an enhanced refinement and modification effect on primary Mg 2 Si. The unique co-modification effect is mainly derived from the synergistic combination of Sb and Zr. Sb can involve in the formation of Mg 3 (Sb, Si) 2 particles and thereby can act as heterogeneous nuclei of primary Mg 2 Si, resulting in the uniform distribution and refined particle size of primary Mg 2 Si crystals. The role of Zr is also indispensable as it can decrease the solidification temperature interval of the primary Mg 2 Si phase, which could further refine the primary Mg 2 Si crystals and promote their complete growth. Moreover, the wear resistance of Al–20Mg 2 Si alloys is also improved owing to the special co-modification effect of Zr and Sb. Since primary Mg 2 Si can be optimized by enhancing heterogeneous nucleation and decreasing solidification temperature interval, such idea can be extended to guide the microstructure control in other alloy systems. Graphical abstract Image 1 Highlights • Fined and polygonal primary Mg 2 Si particles were obtained by adding Zr-Sb. • The wear resistance of Al–20Mg 2 Si alloys was improved due to fined primary Mg 2 Si. • Mg 3 (Sb,Si) 2 particles act as nuclei of primary Mg 2 Si particles. • Zr decreases the solidification temperature interval of primary Mg 2 Si phase. [ABSTRACT FROM AUTHOR]

Abstract In the present work, we investigated the influence of deformation temperature on the formation of a bimodal microstructure and tensile properties of a Mg–9Al–1Zn (AZ91) alloy processed by a single pass hard plate rolling (HPR) with a thickness reduction of 55% followed by a short time annealing. Microstructural examinations by electron backscatter diffraction (EBSD) reveal that there exists a narrow deformation temperature window, i.e. it is only feasible to achieve a desired bimodal grain structure in the AZ91 alloy when HPRed at ∼350 °C. It is mainly because that partial dynamic recrystallization (DRX) occurs easily in the sample HPRed at ∼ 350 °C, facilitating the formation of a bimodal microstructure consisting of coarse un–recrystallized grains (>∼70 μm) and fine recrystallized grains (<∼5 μm). In contrast, reducing deformation temperature to ∼300 °C results in a coarse unrecrystallized microstructure containing substantial sub structure, while elevating the deformation temperature to ∼400 °C leads to an almost uniform recrystallized grain structure. Especially, the formation mechanism for the bimodal grain structure at the optimum deformation temperature is explored in terms of Schmidt factors analysis for basal slips (SF basal ) for grains of different size scales. Moreover, the 350 °C HPRed AZ91 sample exhibits a better combination of strength (ultimate tensile strength = ∼374 MPa) and ductility (elongation = ∼19.6%), as compared to the 300 and 400 °C samples. It is mainly attributed to the typical bimodal grain structure and the relatively high SF basal featured by the fine recrystallized grains as well as the nanometer spherical particles distributing in fine grain interiors. Graphical abstract Image 1 Highlights • A bimodal grain structure of Mg–9Al–1Zn alloy was achieved by tailoring rolling temperature during hard–plate rolling (HPR). • The formation of bimodal microstructure was explored in terms of Schmidt factors analysis for basal slips (SF basal ). • The formation of bimodal grain structure generated a simultaneous improvement of strength and ductility. [ABSTRACT FROM AUTHOR]

Abstract The performances of particulate–reinforced aluminum matrix composites are strongly dependent on alloying elements, precipitates and added particulates. To reveal the sole influence mechanisms of high volume fraction of nanosized particulates on the solidification behavior, microstructure and mechanical properties of aluminum alloys, nanosized SiC P (60 nm) was incorporated into commercial pure Al at different volume fractions (i.e., 0, 1, 3, 5, 7 and 9 vol%) by stir–casting assisted ultrasonic vibration. The results reveal that a fairly uniform dispersion of nanosized SiC P throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average α–Al dendritic sizes were significantly refined from 270 µm for the matrix to 90 µm in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiC P increased the nucleation temperature of α–Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiC P /Al composites at both ambient temperature and 453 K were remarkably improved, whilst remaining suitable fracture strain. Theoretical analysis suggests that the significant strength increments induced by nanosized SiC P at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiC P could predominantly account for the strengthening effect at 453 K. Highlights • Nanosized SiC P refined the microstructure via heterogeneous nucleation and inhibited growth. • SiC P enhanced strengths at 298 K mainly due to thermal mismatch and Orowan strengthening. • Pinning effects of SiC P on grain boundaries and dislocation climbing enhanced strengths at 453 K. [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]

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]

In this paper, the 4 vol% SiC p /Al-Cu-Mg-Si-Mn composites were prepared by method of stirring casting. The effects of SiC p surface modifications (oxidization and Ti-coating) and particle sizes (5 μm, 10 μm and 15 μm) on the microstructure and tensile properties of the composites were analyzed. The effects of SiC p sizes on the distribution of SiC p in the pre-oxidized SiC p /Al-Cu-Mg-Si-Mn composites were larger than those in Ti-coated SiC p /Al-Cu-Mg-Si-Mn composites. The Al-Cu-Mg-Si-Mn composites reinforced with Ti-coated SiC p exhibited more uniform SiC p distributions and higher tensile mechanical properties than those reinforced with the pre-oxidized SiC p . When the SiC p size was 15 μm, the Ti-coated SiC p /Al-Cu-Mg-Si-Mn composite showed the best yield strength (σ 0.2 ), ultimate tensile strength (σ UTS ) and fracture strain (ε f ) of 410 MPa, 548 MPa and 7.6% with the increase of 10.2%, 2.6% and 5.6% than that of reinforced by pre-oxidized SiC p . The more uniformly dispersed particles and better tensile properties of the Ti-coated SiC p /Al-Cu-Mg-Si-Mn composites could be attributed to the better wetting between Ti-coated SiC p and molten Al. [ABSTRACT FROM AUTHOR]

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al Si eutectic and Al 2 Cu. As a result, the optimal microstructure is composed of finer α-Al grains, Al 2 Cu and more rounded primary and eutectic Si, with sizes decreased to ∼52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si-5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer α-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 °C, and 28.3% and 10.8% at 300 °C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency. [Display omitted] • Fully microstructure-manipulated alloy was made via adding trace nanoparticles. • Nanosized ZrCu(B2) and Zr 2 Cu have ideal lattice mismatch with Si, α-Al and Al 2 Cu. • The sizes of primary Si, α-Al, eutectic Si and Al 2 Cu decreased simultaneously. • The tensile strength and elongation of manipulated alloy are greatly improved. [ABSTRACT FROM AUTHOR]

Forging and welding are common necessary procedures for AA6××× alloys, and recrystallization is an inevitable process. However, it is still difficult to realize the control of the recrystallization behavior, while realizing the strengthening of mechanical properties of the base metal and welded joint. In this study, we overcome this problem through 0.5 wt% TiC–TiB 2 nanoparticles, and fully reveal the influence of the nanoparticles on the recrystallization behavior of the base metal and nugget zone of a friction-stir-welded (FSW)-ed joint from the perspectives of dislocation rearrangement and grain boundary motion. The strengthening mechanisms of the base metal and FSW-ed joint are clarified. The recrystallization driving force of the base metal and nugget zone was increased. Dislocations with a higher density rearranged and formed more grain boundaries in the nugget zone. Besides, nanoparticles distributed on the grain boundaries restrained the vanishing of low-angle grain boundaries. The nugget zone microstructures were refined from 3.1 to 2.3 μm, and the recrystallization ratio was increased from 7.2% to 10.4% at 800 rpm. The grains in the nugget zone were refined from 2.2 to 1.9 μm, and the recrystallization ratio was increased from 16.1% to 18.4% at 1200 rpm. The promoted recrystallization in the nugget zone accelerated the release of stress. Nanoparticles weakened the precipitate coarsening in the nugget zone. After strengthening, the ultimate tensile strength and plastic strain of the FSW-ed joint at 800 rpm were increased by 4.7% and 18.8%, respectively. This study provides new approaches for a systematic microstructure evolution control in FSW-ed 6061 Al alloys. • Trace nanoparticles double the recrystallization driving force of base metal. • More dislocation tangles promoted recrystallization of nugget zone. • Nanoparticle also inhibited grain coarsening of nugget zone. • Precipitate coarsening in the nugget zone was weakened. • FSW-ed joint softening was alleviated and the mechanical properties were enhanced. [ABSTRACT FROM AUTHOR]

The Al-Cu-Mg-Si matrix composites reinforced with in situ hybrid-sized TiC x -TiB 2 particles with sizes ranging from 20 nm to 1.3 µm were successfully synthesized using the Al-Ti-B 4 C reaction system via a method that combined the combustion synthesis and the hot press assisted with hot extrusion. The sizes of the fabricated TiC x and TiB 2 particles increased with increasing TiC x -TiB 2 content. The hybrid-sized TiC x -TiB 2 particles improved the elevated-temperature yield strength ( σ .2 ), the tensile strength ( σ UTS ), and the fracture ductility ( ε f ) of the composites at both 493 K and 573 K. The 40 wt% (TiC x -TiB 2 )/Al-Cu-Mg-Si composite exhibited superior σ .2 (141 MPa), σ UTS (164 MPa), and ε f (31.2%) at 573 K, with enhancements of 60.2%, 72.6%, and 22.4% compared to the Al-Cu-Mg-Si matrix alloy (88 MPa, 95 MPa, and 25.5%). The improvement of the elevated-temperature mechanical properties for the in situ (TiC x -TiB 2 )/Al-Cu-Mg-Si composites was attributed primarily to the strengthening effects induced by the hybrid-sized TiC x -TiB 2 particles and the θ′ precipitation strengthening. [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]

In the present work, Mg-9Al-1Zn-0.4Sn (AZT910) magnesium alloy sheets with a fine-grained structure (∼5 μm) and tilting basal texture were prepared by a 16-passes rolling process. Effect of tensile directions on properties and microstructural evolutions of the AZT910 alloy sheet at different temperatures, i.e. room temperature, 200 and 300 °C, respectively, were investigated by using three kinds of tensile specimens (rolling direction (RD), transverse direction (TD) and 45° towards RD). Experimental results showed that tensile properties exhibited a strong dependence on tensile directions at room temperature and 200 °C, while a negligible dependence at 300 °C. The anisotropic tensile properties imply that the deformation system of rolled AZT910 sheet consists of basal and non-basal slips at room temperature, and is a combination of basal slip, non-basal slip and grain boundary sliding/rotation (GBS) at 200 °C. The decrease of intensity and spreading of basal poles during tensile test and isotropic tensile properties indicates that GBS becomes the dominate deformation mechanism at 300 °C. The present work provides reference for the study of deformation behavior of novel superplastic magnesium alloy, and hence is of great significance for further application of wrought magnesium alloy. [ABSTRACT FROM AUTHOR]

The bimodal-sized (micron+nano) TiC p /Al-Cu composites were successfully fabricated by adding the in situ micron-sized and nano-sized TiC p -Al master alloys into the molten Al-Cu alloy. The composites reinforced with bimodal-sized TiC p exhibited finer α-Al grains and smaller θ′ precipitates, and possessed enhanced room- and high-temperature strength and relatively high ductility compared with the Al-Cu matrix alloy and their counterparts reinforced with monomodal-sized TiC p . The improved tensile properties may be attributed to the more significant precipitation strengthening due to the smaller θ′ precipitates, grain refinement and strengthening effects of the nano-sized and micron-sized TiC p . [ABSTRACT FROM AUTHOR]

Mesoporous nanoring-like Zn-Co mixed oxides are synthesized via a simple template-free solvothermal method with a subsequent annealing process. The ring-like nanostructures with hollow interiors are formed under the complexing effects of potassium sodium tartrate. Numerous mesopores are generated after the precursor is annealed at 500 °C. When applied as anode materials, the mesoporous nanoring-like Zn-Co mixed oxides can deliver a high discharge capacity of 1102 mAh g −1 after 200 cycles at 500 mA g −1 . Even when the current density is increased to 2 A g −1 , the mixed oxides can still retain a reversible capacity of 761 mAh g −1 . Such high cycling stability and rate capability are mainly derived from the unique mesoporous ring-like nanostructures and the synergistic effects between Zn and Co based oxides. [ABSTRACT FROM AUTHOR]

In this study, the structural stability and electronic properties of Al(111)/4H-SiC(0001) interface, as well as the effects of Ti, Si, Mg and Cu additions on the interfacial adhesive strength are investigated via the first-principles method. Surface energy calculations show that 4H-SiC(0001) with C-termination is more active than Si-termination. Moreover, polar covalent bonds are formed across Al/4H-SiC interface. The results of separation energies suggest that the introduction of Ti and Si can improve the adhesive strength of C-terminated Al(111)/4H-SiC(0001) interface, whereas Mg and Cu have the opposite effect. According to the analysis of interfacial electronic structure, the covalent bonds across Al/4H-SiC interface are further enhanced with the addition of Ti and Si atoms, contributing to the improved adhesive strength in this case. However, the interactions between interfacial atoms are weakened with Mg and Cu doped in C-terminated interface, which results in the decrease of interfacial adhesion strength. Our calculations provide a guide to experiments on the design of 4H-SiC reinforced Al-matrix composites with tailored properties. [ABSTRACT FROM AUTHOR]

A design map in regard to the generalized-stacking fault (GSF) energy is plotted for Ti 5 Si 3 (Ti 60 Si 36 ) alloying with 12 ternary elements in { 1 1 ¯ 00 } [ 0001 ] slip system. Hereinto, alloying elements occupy preferable Ti sites near slip planes. The elements with a larger radius difference from Ti tend to reduce the GSF energies more dramatically. Moreover, the elements smaller than Ti are more prone to decreasing GSF energies than those larger than Ti. Accordingly, the addition of ternary elements, like Ni, Cu and Co, will lead to an obvious decrease in GSF energies by 18.0%, 16.7% and 13.4% respectively, and therefore may facilitate the initiation of prismatic stacking faults and furthermore enhance ductility. Note that the decline of GSF energies is attributed to the weakening covalent bonds between slip planes with the introduction of ternary elements. Our calculations provide a guide to experiments on the design of Ti 5 Si 3 compounds with tailored properties. [ABSTRACT FROM AUTHOR]

We developed a novel and simple bidirectional freeze-casting technique to prepare porous ceramics with long-range ordered lamellar structures in three dimensions (3D). A side copper or stainless-steel plate was used as the cold source to generate dual temperature gradients for the control of the nucleation and growth of ice crystals. The Al 2 O 3 architectures prepared with the side copper plate exhibited well-assembled lamellar structures with abundant cross connections of the ceramic lamellae. The compressive strength of the resultant Al 2 O 3 architectures with ∼ 50% porosity reached 158 ± 3 MPa in the primary freezing direction and 42 ± 6 MPa in the secondary freezing direction, ∼ 32% and ∼ 130% higher than that of the counterparts prepared by unidirectional freeze casting. In contrast, the Al 2 O 3 architectures prepared with a side stainless-steel plate exhibited thicker ceramic lamellae and wider pore channels as well as decreased cross connections, leading to much weaker compressive strength. [ABSTRACT FROM AUTHOR]

In this work we proposed a novel strategy for spontaneous infiltration of molten Al into a porous lamellar Y 2 O 3 partially stabilized ZrO 2 (PSZ) architecture prepared by using an ice-templating method. The kinetics of liquid spreading and infiltration under the application of a 10 mA current was investigated. The electrochemically-induced improvement in wettability greatly facilitated the spontaneous infiltration. [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]

In the present study, the application of hard–plate rolling (HPR) on the hard-to-deform Mg–7Al–5Zn (AZ75) alloy resulted in a homogeneous fine grained (∼6 μm) microstructure, where numerous micron/nano Mg 17 (Al, Zn) 12 precipitates with spherical morphology uniformly dispersed both at grain boundaries and within grain interiors. More importantly, the HPRed AZ75 alloy exhibited superior mechanical properties with a simultaneous high strength and ductility at room temperature, i.e. yield strength (YS) of ∼218 MPa, ultimate tensile strength (UTS) of ∼345 MPa and elongation of ∼19%, which was comparable to the commercial wrought magnesium alloys. According to the contribution from the several strengthening mechanisms estimated by simplified models, the grain boundary strengthening is the predominant mechanism for the high YS of the alloy. The high ductility is benefited from the strong work-hardening capacity resulted from Zn solid solutes and the presence of numerous well-dispersed nanosized precipitates as well as weakened texture. Moreover, the fine grained AZ75 alloy exhibits an optimum superplasticity of ∼615% at 300 °C at 1 × 10 −3 s −1 . It is attributed to the enhanced grain boundary slip (GBS) promoted by a well maintained fine grain structure resulted from the pining effect by numerous Mg 17 (Al, Zn) 12 particles segregating along grain boundaries during tension. The results will be helpful for the development and processing of high alloying element content Mg alloys with high strength and ductility as well as enhanced formability. [ABSTRACT FROM AUTHOR]

The coarse segregative eutectic phases, emerged in the twin roll casting (TRC) process of Mg strips, which cannot be resolved solely by controlling the processing variables or post heat treatment, are detrimental to the subsequent rolling deformation. Considering it, we introduce the pre-rolling steps on the TRC Mg-4Al-2Sn-1Zn (ATZ421) alloys, which is expected to facilitate the dissolution of these segregative phases by increasing distortion of crystal lattices and rolling stress, and further investigate the effect of a single pass or two passes pre-rolling on the microstructure evolution and tensile properties. It indicates that the pre-rolled alloy with two passes presents more uniform precipitates and higher twinning density in comparison with that using a single pass. The uniform distribution of precipitates in two passes pre-rolling is due to the increase in density of dislocations and deformed twins, which results in more distortion of crystal lattices with more stored energy, facilitating the diffusion of solutes. Moreover, the pre-rolling of two passes introduces more rolling stress into Mg matrix, which is beneficial for the crush of coarse eutectic phases, and further accelerates the sufficient dissolution of second phases. After the subsequent rolling and annealing processes, the sheet with pre-rolling deformation of two passes shows finer microstructure, which mainly benefits from the pinning effects of uniform nano-sized precipitates. As a result, the annealed sheet with two-pass pre-rolling deformation exhibits an advantageous combination of high strength and high ductility with fine microstructure, showing an ultimate tensile strength of ~297 MPa, a yield strength of ~ 205 MPa and an elongation of 25.0%. This work provides an effective method of dissolving the coarse segregative phases in the TRC Mg alloys with significant potential for industrial production. [ABSTRACT FROM AUTHOR]

Freeze casting has been proven to be a versatile processing approach for the design of biomimetic composites that exhibit unique combinations of strength and toughness. However, to date, most studies have focused on polymer–ceramic composites, and very limited work has examined metal–ceramic composites, even though the latter possess much superior mechanical properties. In this work, we prepared nacre-like Al/Al 2 O 3 –ZrO 2 composites using freeze casting and pressure infiltration techniques and then investigated the influences of the ceramic lamellae compactness and interface reaction on the mechanical properties and fracture behavior of the composites. The results show that the compactness of the ceramic lamellae greatly influences the Al penetration and subsequent interfacial reaction with ZrO 2 . The presence of Al 3 Zr reaction product layers facilitates crack initiation and interface debonding, weakening the fracture toughness of the composites. The ceramic lamellae can be densified by using fine ceramic particles and increasing the ceramic loading and sintering temperature, thus greatly reducing the extent of the interfacial reaction and improving the strength and toughness of the materials. [ABSTRACT FROM AUTHOR]