Search

In this work, squeeze casting experiments of flywheel housing components with a large wall thickness difference and a complex shape were carried out with AlSi9Mg aluminum alloy. The defects, microstructures, and mechanical properties under different process parameters were investigated. Furthermore, the local pressurization process was applied to the thick-walled positions to force-feed the cast defects. The mechanical properties and microstructures at these positions were analyzed. The results showed that the surface quality of formed components was good and that local pressurization could effectively reduce the shrinkage cavity and shrinkage porosity in thick walls, but the scope and effect of forced feeding were limited. The optimum process parameters were a pouring temperature of 650 °C, a specific pressure of 48 MPa, a mold temperature of 220 °C, a local pressurization of 800 MPa, and pressure delay times of 15 s (side A) and 17 s (side B). The ultimate tensile strength, yield strength, and elongation of the formed component under validation experiments of the optimum process parameters were 201 MPa, 103 MPa, and 5.1%. Meanwhile, the fine grains of primary α-Al were mainly rosette and equiaxed grains, and the average grain size was about 40 μm. The microstructure of the eutectic silicon was acicular and was prone to segregation under pressure. According to profile morphology, the positions after pressurization were divided into a deformation zone, a direct action zone, and an indirect action zone. The coexistence of as-cast and plastic deformation microstructures was observed. The effect of local pressurization mainly involved a change in the solidification process, plastic deformation, and forced feeding. [ABSTRACT FROM AUTHOR]

The relationship among microstructure, mechanical properties, and corrosion behavior of an Al7.5Co20.5Fe24Ni24Cr24 high‐entropy alloy (HEA) is systematically studied. The as‐cast HEA consisted of a single face‐centered cubic (FCC) phase with negligible chemical inhomogeneities of Al and Ni elements, whereas the homogenized HEA displayed a single FCC supersaturated solid‐solution phase with uniform distribution of constituent elements. Homogenization followed by aging at 900 and 700 °C leads to the formation of different precipitates in the FCC matrix. As the variety and volume fraction of precipitates increased, the HEA samples accordingly show enhanced strengths accompanied by slight losses in ductility. However, the formation of L12, B2, and σ precipitates is detrimental to the electrochemical properties of the HEAs. Improving the homogeneity of elemental distribution leads to a higher content of Cr oxides and Co(Fe,Cr)2O4 complex oxides in the passivation film, rendering an enhancement of corrosion resistance of the HEA in sulfuric acid. This work reveals the influence of chemical inhomogeneities and precipitates on the mechanical and electrochemical properties of the FCC‐structured Al7.5Co20.5Fe24Ni24Cr24 HEA via tuning phase composition, providing an interesting insight into how to balance the structural (strength and ductility) and functional (anti‐corrosion) properties of HEAs. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO)/epoxy composites cured by aliphatic dibasic acids have been prepared. The influences of structure of aliphatic dibasic acid and loading of GO on curing process and mechanical properties of epoxy composites were studied. The results show that the reaction activities, gel time of corresponding epoxy‐acid system and tensile strength of the formed epoxy resins decrease with the increase of the chain length of aliphatic dibasic acids. Both fracture toughness (>1.96 MPa⋅m1/2) and elongations at break (>6%) increase with the increase of the chain length of aliphatic dibasic acids. The introduction of GO is helpful to increase the mechanical properties and the gas transmission coefficient of GO/epoxy composites. A maximum of tensile strength and elongations at break were obtained when the loading of GO is 0.6 wt%. The gas transmission coefficient of GO/epoxy composite increases with the increase of GO loading. The excellent mechanical properties and gas leakage resistance coefficient of the formed epoxy composites provides potential application in many fields where conventional brittle epoxy resins are inapplicable. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To develop the functional particles with better flame‐retardant and compatibility with epoxy resin (EP) matrix, organic–inorganic double‐shell microencapsulated aluminum hypophosphite (MSiAHP) was prepared by situ polymerization. The water contact angles of MSiAHP (62.4°) is significantly larger than that of aluminum hypophosphite (34.4°), which shows that the organic shell material of MSiAHP endows excellent hydrophobicity and water resistance. With the incorporation of MSiAHP, EP/30%MSiAHP composite exhibits limiting oxygen index value of 27.3% and V‐0 rating. Furthermore, the cone calorimetry test reveals that MSiAHP reduces the peak heat release rate, total heat release and total smoke release of EP matrix by 33.3%, 24.4% and 56.6%, respectively. Besides, due to the unique organic–inorganic double‐shell structure of MSiAHP particles, EP/30%MSiAHP composite achieves greater thermal stability and higher char yields than pure EP. The investigation of the products in the gas and condensed phase demonstrates that MSiAHP is beneficial to the generation of a high‐density and compact carbon layer structure with a high graphitization degree, and delay the generation time of pyrolysis products in the gas phase, which can improve the fire safety of EP composites effectively. Furthermore, preeminent dispersion and compatibility of MSiAHP lead to EP/MSiAHP composites with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) as an excellent nanofiller is widely used to improve the mechanical properties of the resin matrix. The dispersion and distribution of GO sheets in the resin matrix have a strong impact on the mechanical properties of composites. Based on the action principle of GO sponge, a simple method for solving the highly and aligned dispersion of GO in the bismaleimide (BMI) resin is investigated. The GO bulk prepared by vacuum infusion using a porous GO sponge as a frame is smashed in the resin by the large shear force generated through the high‐speed stirring method. It is found that GO sheets have a highly dispersion in the BMI resin. A sample and new method for preparing GO aligned dispersion in resin by large deformation is provided to further enhance the mechanical properties of the resin. As expected, the flexural strength and flexural modulus of GO/BMI nanocomposites are enhanced by 39.6% and 45.5% than BMI resin. This simple dispersion method is easier to generalize to solve the dispensability of GO in other kinds of resins. In the future, there will be a broader application prospect in engineering applications. [ABSTRACT FROM AUTHOR]

Abstract Thixoforging experiments on SiC particles (SiC p) reinforced AZ91 magnesium (Mg) matrix composites (AZ91-SiC p) were conducted under different forging temperatures and forging loads. The microstructures and mechanical properties of the thixoforged AZ91-SiC p samples were investigated experimentally by microstructural analyses, hardness tests, tensile tests, and compression tests. AZ91-SiC p semisolid slurries exhibited different forming behaviors at different temperatures, because the different volume fractions and morphologies of the liquid phase, SiC p , and α-Mg in them at different temperatures. The outflow of the liquid phase not only inhibited crack formation on the surface of the thixoforged samples but also resulted in segregations of intermetallic compounds and SiC p in the thixoforged samples. Mechanical properties of the thixoforged samples affected significantly by the volume fraction and distribution of brittle Mg 17 Al 12 intermetallic compounds surrounding α-Mg and SiC p transformed from liquid phase during cooling. Higher forging temperatures improved the outflow of the liquid phase during thixoforging and resulted in thixoforged samples more inhomogeneous distributions of microstructures and mechanical properties. Forging load did not significantly affect the outflow of the liquid phase during thixoforging or the inhomogeneity of the microstructure of thixoforged samples. Higher forging loads caused higher residual stresses in the bottom regions of the thixoforged samples, which resulted in higher values of hardness in these regions. Highlights • Cup-shaped parts of AZ91-SiC p were fabricated by thixoforging. • Effects of SiC p and Mg 17 Al 12 on mechanical properties of AZ91-SiC p were revealed. • Effects of forging parameters on microstructure of AZ91-SiC p were studied. • Effects of forging parameters on mechanical properties of AZ91-SiC p were studied. [ABSTRACT FROM AUTHOR]

ABSTRACT: Poly(3hydroxybutyrate‐co‐4hydroxybutyrate) [P(3HB‐co‐4HB)]/graphite oxide (GO) composites were fabricated using a solution mixing method. The GO structures in the composites were analyzed by using transmission electron microscopy, Raman spectroscopy, and X‐ray diffraction. The fracture morphology of the samples was evaluated by the multifractal, and the effect of GO dispersion on the mechanical properties and the thermal stability were discussed for the P(3HB‐co‐4HB) and the composites. It was found that the interlayer spacing of the GO increased due to the intercalation of the polymer into the GO platelets. As the GO content increased, the relative multifractal spectrum increased, but the mechanical properties declined for the composites, indicating that the filler agglomeration effect overcame the reinforcement benefits for the high loadings of the GO. Moreover, both good dispersion and high content of the GO platelets increased the thermal stability of the composites. Therefore, the relative multifractal spectrum width of the fracture morphology was related to the mechanical properties and the thermal stability of the composites. [ABSTRACT FROM AUTHOR]

Because of hexagonal crystal structure, magnesium alloys, especially magnesium alloys with addition of rare earths, exhibit poor formability at room temperature. The isothermal precision forging process at elevated temperature can improve the formability of magnesium alloys. In this paper, the isothermal precision forging process of the complex shape case of Mg-Gd-Y-Zn-Zr magnesium alloy was simulated based on FORGE Nxt. A two-stage isothermal precision forging process was determined. According to the simulation results, isothermal precision forging experiments of magnesium parts with high performance and complex shape were successfully carried out. After isothermal precision forging process, the cases of magnesium alloy were subjected to heat treatment. Moreover, the mechanical properties of parts were also determined. [ABSTRACT FROM AUTHOR]

Double-network (DN) hydrogel has intrinsic tough mechanical properties due to its unique two contrasting network structures. The research on DN hydrogel is a fast growing field, mainly focusing on network structures, formation, and interactions at the molecular level. In this trend article, we take a critical review at the important and latest research findings, current research challenges, and future research directions in the DN hydrogel field. We discuss some issues on the discovery of fundamentally new phenomena versus performance benchmarking for different types of the DN hydrogels. Finally we offer our personal opinions to several unique aspects for future DN gel research. [ABSTRACT FROM AUTHOR]

The Mg–Zn–Y–Zr alloys, which exhibit high strength and high elongation, have great potential for applications in many fields, such as automotive, aircraft, and aerospace industries. However, plastic deformation behavior under hot compression is still not fully understood. Hot compression tests of extruded Mg–Zn–Y–Zr alloy were performed at temperatures from 250 °C to 450 °C and strain rates from 0.001 s −1 to 1 s −1 . A constitutive equation and processing map were developed to describe the flow characteristics. In addition, isothermal forging tests were conducted to verify the optimal deformation parameters. The results show that the strain rate and deformation temperature exert remarkable influences on the flow stress. The average activation energy and the stress exponent of deformation were determined as 137.400 kJ/mol and 3.707, respectively. The efficiency of power dissipation was high for all deformation conditions compared to the cast Mg–Zn–Y–Zr alloy, and the processing map exhibited four domains with high efficiency of power dissipation. The optimal deformation temperatures and strain rates for extruded Mg–Zn–Y–Zr alloy were 350–400 °C and 0.001–0.1 s −1 , respectively. Components were prepared successfully according to the optimal deformation temperature and strain rate, which exhibited good surface quality and no deformation defect. The component after aging treatment exhibited an ultimate tensile strength of 396 MPa, a yield strength of 356 MPa and an elongation of 5.2%. [ABSTRACT FROM AUTHOR]

Accumulative plastic deforming (APD) at multistep temperatures was induced into the recrystallization and partial melting (RAP) route as a novel predeformation method to replace conventional upsetting or extrusion. AM60 magnesium alloy ingots with diameter of 520 mm were produced by semi-continuous casting, and semi-solid slugs with diameter of 320 mm were prepared by partial remelting of as-cast and APD formed alloys. The microstructure evolution during semi-solid remelting was investigated. The tensile mechanical properties of AM60 alloy at room temperatures were determined. The results show that large semi-solid AM60 alloy slugs with fine and homogeneous microstructures can be produced by employing APD in RAP route, and the microstructure consists of spheroidal solid grains surrounded by intergranular liquid matrix. The as-cast AM60 alloy during partial remelting showed inferior microstructures with coarsened solid grains and high proportion of intragranular liquid droplets. During partial remelting, coalescence and Ostwald ripening are dominant in as-cast alloy and APD formed alloy, respectively. The formation and migration mechanism of intragranular liquid droplets were discussed. Although both of APD formed and as-cast AM60 slugs could fill the die during thixoforming process, the tensile mechanical properties of the components thixoformed from APD formed alloys far exceed those from the as-cast alloys. [ABSTRACT FROM AUTHOR]

Multidirectional forging (MDF) was applied to severely deform the homogenized coarse-grained Mg–Gd–Y–Nd–Zr alloy under decreasing temperature condition, and the microstructure, texture and tensile properties of the MDFed alloy were investigated in the current study. With the increase of MDF passes, the volume fraction of the fine recrystallized grains was remarkably increased, and the average grain size decreased from 200 μm to 5.4 μm after three MDF passes, but after that, the average grain size was almost unchanged, ultrafine grains (UFGs) with an average grain size of 5.1 μm were uniformly evolved after six MDF passes. The basal texture was gradually weakened with increasing the MDF passes, which resulted from cooperative effect of dynamic recrystallization, dynamic precipitation and the change direction of the MDF force. The yield strength, ultimate tensile strength and elongation to failure were enhanced with increasing the MDF passes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot deformation behavior of as-extruded Mg–Gd–Y–Zn–Zr alloy was studied. [•] The hot deformation behavior was studied by processing maps. [•] The optimum parameters for hot working of the tested alloy were obtained. [•] Three components were successfully prepared according to the determined hot deformation parameters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Reheating from the extruded alloy is shown to produce ideal semi-solid structures. [•] The as-cast alloy exhibits non-uniform microstructures. [•] The as-cast alloy is not as thixoformable as the extruded alloy. [ABSTRACT FROM AUTHOR]

Hot workability of conventional magnesium alloys, such as AZ61, AZ80 and ZK60, have been proposed or reported in previous literature. However, no detailed investigation has been conducted regarding the hot workability of as-cast Mg–Zn–Y–Zr alloy. The hot deformation characteristics of as-cast Mg–Zn–Y–Zr alloy were investigated using constitutive equations and processing maps at temperatures between 200 and 400°C and strain rates ranging from 0.001 to 1s−1. Backward extrusion of the component with multi-hole was carried out to evaluate the workability of Mg–Zn–Y–Zr alloy at elevated temperatures. The results show that the flow stress has been found to be strongly dependent on temperature as well as strain rate. By means of regression analysis for the Arrhenius type equation of flow behavior, the apparent average activation energy of deformation was determined as 251.228KJ/mol, and the stress exponent was 6.231. The processing map technique was utilized to determine the practical processing parameters. The reasonable process parameters of as-cast Mg–Zn–Y–Zr alloy were deformation temperatures of 350–400°C and stain rates of 0.001–0.1s−1. The reproduction of Mg–Zn–Y–Zr alloy components with multi-hole was shown to be good, and no problem was experienced in filling during backward extrusion using reasonable process parameters. [ABSTRACT FROM AUTHOR]

Abstract: The present work deals with the microstructural evolution and mechanical properties of 7A09 aluminium alloy in four different conditions, including as-received, annealed, cold-extruded and heat treated conditions. The results indicate that 7A09 alloy treated by annealing can be backward extruded successfully at room temperature with an extrusion ratio of 4. After annealing, although the degree of recrystallisation increases, unrecrystallised grains still exist. Associated with the decrease in tensile strength is an increase in ductility in the 7A09 alloy during annealing. Backward extrusion at room temperature indicates that the strengths of the alloy are moderately improved at the expense of decrease in ductility. After heat treatment (T6), fine precipitates uniformly distribute in the alloy and are very effective in restricting dislocation movement during deformation. Good ultimate tensile strength (590MPa) is obtained for the alloy treated by heat treatment (T6), with a yield strength of 522MPa and an elongation to fracture of 10%. The tensile properties of 7A09 alloy in the heat treated condition are a little better than those of 7A09 alloy in the as-received condition. Moreover, dimensional accuracy and surface roughness of 7A09 alloy treated by backward extrusion at room temperature plus heat treatment are also satisfied with the requirement. [Copyright &y& Elsevier]

Abstract: In this letter, inspired by multiscale structures of natural tissues, we propose a porous bioscaffold with structural hierarchy to optimize tissue regeneration. By describing its geometric model and performing mechanical analysis, Young’s modulus and strength of the scaffold, which can be formulated with given parameters of the bottom level, are derived by an iterative method. Theoretical predictions on the two mechanical parameters by the present method are compared with others by the homogenization theory and power law; the comparison shows that they agree very well. The porous scaffold could be applied in future tissue engineering as a new biomaterial. [Copyright &y& Elsevier]

Abstract: Natural selection and evolution develop a huge amount of biological materials in different environments (e.g. lotus in water and opuntia in desert). These biological materials possess many inspiring properties, which hint scientists and engineers to find some useful clues to create new materials or update the existing ones. In this review, we highlight some well-studied (e.g. nacre shell) and newly-studied (e.g. turtle shell) natural materials, and summarize their hierarchical structures and mechanisms behind their mechanical properties, from animals to plants. These fascinating mechanisms suggest to researchers to investigate natural materials deeply and broadly, and to design or fabricate new bio-inspired materials to serve our life. [Copyright &y& Elsevier]

Abstract: As-cast Mg–Zn–Y–Zr magnesium alloy is subjected to forward extrusion in different conditions. The results show that mechanical properties of Mg–Zn–Y–Zr alloy remarkably deteriorate when extrusion temperature increases from 400°C to 450°C because of grain coarsening. Significant improvement in mechanical properties of the alloy can be obtained with increasing extrusion ratio from 0 to 25. However, when the extrusion ratio increases from 25 to 100, the mechanical properties of the alloy almost remain the same. The retardation of recrystallisation in the alloy is dominated by the presence of Mg–Zn–Y particles. Solution treatment at 510°C (T4) causes complete recrystallisation and decrease of mechanical properties. Aging at 160°C (T5) causes increase in both strengths and ductility of extruded alloy. In isothermal backward extrusion, the as-cast Mg–Zn–Y–Zr alloy exhibits an excellent workability at temperatures from 250°C to 400°C with a extrusion rate of 10mm/s. Temperatures higher than 400°C are not suitable for forming of the alloy because of heavy oxidation. [Copyright &y& Elsevier]

Abstract: The Mg–5.3wt.%Zn–1.13wt.%Nd–0.51wt.%La–0.28wt.%Pr–0.79wt.%Zr alloy prepared by direct chill casting is subjected to hot extrusion. The effects of extrusion ratio and temperature on microstructure and tensile mechanical properties have been studied. The results indicate coarse grains of as-cast alloys are refined with extrusion ratio increasing from 0 to 9. The eutectic constituents are elongated along extrusion direction. However, further increase of extrusion ratio has a little influence on grain refinement and the improvement of mechanical properties of the alloy. Dynamic recrystallisation is the main mechanism of grain refinement during hot extrusion. Raising extrusion temperature results in grain coarsening. Grain shape becomes more equiaxed-like with raising extrusion temperature. At the same time, mechanical properties decrease with the increase of extrusion temperature. [Copyright &y& Elsevier]

Abstract: A multitemperature multi-axial forging (MAF) procedure has been developed to produce a fine-grained AZ61 alloy. The results show that the microstructure can be effectively refined with increasing equivalent strain during MAF. Once dynamic recrystallisation is completed, the alloy is in a steady state and further deformation of the alloy cannot change the grain size. The multitemperature MAF procedure can produce a fine-grained AZ61 alloy giving a grain size of 8μm. This fine-grained alloy has an excellent strength accompanied by reasonable good tensile ductility. The success of the development of this multitemperature MAF procedure proves that MAF can offer a good opportunity for the development of magnesium alloys with good mechanical properties. [Copyright &y& Elsevier]

Abstract: Aluminum silicate fiber (ASF)/hollow mesoporous silica microspheres (HMSM) composites were fabricated by a vacuum filtration technique, followed by pressureless sintering at 1100°C. Properties namely: bulk density, microstructure, mechanical strength and thermal conductivity were investigated with the ASF content. Results showed that bulk density of the resultant composites increased from 0.17 to 0.26g/cm3 with the increase of ASF content, and the ASF was intimately bonded to the HMSM matrix. When the ASF content was 15wt.%, the composites exhibited the highest compressive strength (5.07MPa) and flexural strength (3.32MPa), then the mechanical strength decreased on further addition (20wt.%). The thermal conductivity of composites ranged from 0.048 to 0.081W/(mK) at room temperature, which makes aluminum silicate fiber/hollow mesoporous silica microspheres composites a promising choice for thermal insulation. [Copyright &y& Elsevier]

Abstract: Thixoforging requires feedstock having a non-dendritic, equiaxed microstructure, which in some cases can be obtained by the recrystallization and partial (RAP) melting route. Based on the RAP route, squeeze casting–solid extrusion followed by partial melting is proposed to obtain the semi-solid feedstock for thixoforging. After squeeze casting–solid extrusion, unrecrystallized grains were elongated along the extrusion direction. As the temperature rises into the semi-solid regime, there is a sudden increase in the appearance of spheroidal grains. The occurrence of recrystallized grains is closely associated with the location of the first liquid to form above the solidus. Grain coarsening in the semi-solid state can be described by classical LSW equation in Ostwald ripening. The coarsening rate does decrease with increasing solid fraction, f s , for f s less than approximately 0.70, and then increases again with further increasing f s . With prolonged holding time, the grains coarsen and mechanical properties of thixoforged components decrease. Moreover, the AZ91D-RE thixoforged from starting materials produced by squeeze casting–solid extrusion followed by reheating at 570°C for 5min have extremely fine and uniform microstructure. The tensile mechanical properties of squeeze casting–solid extrusion formed AZ91D-RE are better than those of AZ91D-RE thixoforged from starting materials produced by squeeze casting–solid extrusion followed by partial melting. [Copyright &y& Elsevier]

Abstract: Thixoextrusion involves processing alloys with a spheroidal microstructure in the semi-solid state. Before thixoextrusion, repetitive upsetting-extrusion (RUE) is introduced into the strain induced metal activation (SIMA) process to predeform AZ80 magnesium alloy. Microstructure evolution of RUE formed AZ80 magnesium alloy during partial remelting is studied at temperatures for times. Tensile mechanical properties of thixoextruded components are determined and compared with those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. The results show that with increasing number of RUE passes solid grain size decreases and the rate of liquation is improved. Prolonged holding time results in grain coarsening and the improvement of degree of spheroidization. The variation of the solid grains with holding time obeys the Lifshitz, Slyozov and Wagner law. Increasing the heating temperature is favorable for the formation of spheroidal solid grains. The tensile properties for AZ80 magnesium alloy thixoextruded from starting material produced by RUE are better than those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. [Copyright &y& Elsevier]

Abstract: Based on conventional extrusion and equal channel angular extrusion (ECAE), a new severe plastic deformation (SPD) method called compound extrusion is developed to fabricate fine-grained AZ91D magnesium alloys. The fine grain size of 6μm is obtained as the accumulated strain increased to 9.146. The AZ91D alloy treated by compound extrusion exhibits good mechanical properties, with a yield strength of 202.2MPa, a tensile strength of 323.1MPa and an elongation to fracture of 14.8%. The good mechanical properties of AZ91D alloy treated by compound extrusion are due to grain refinement and to the homogeneous distribution of intermetallic particles. The success in development of compound extrusion proves that compound extrusion can offer a good opportunity for the development of good mechanical properties of as-cast magnesium alloys. [Copyright &y& Elsevier]

Abstract: An as-cast Mg–Al–Y–Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225–400°C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg–Al–Y–Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250°C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg17Al12 was elongated along the extrusion direction. With increasing processing temperature to 350°C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg–Al–Y–Zn alloy. Then billets of as-cast Mg–Al–Y–Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably. [Copyright &y& Elsevier]

Abstract: Cyclic closed-die forging (CCDF) was introduced into the strain induced melt activation (SIMA) route to replace conventional upset or extrusion. The microstructure evolution of CCDF formed AM60B magnesium alloy heated into the semi-solid state has been investigated. Tensile mechanical properties for AM60B magnesium alloy thixoformed from starting material produced by the SIMA route were determined. The results show that the SIMA route (four-pass CCDF and partial remelting) produced ideal, fine semi-solid microstructure, in which completely spheroidal primary solid grains had a little amount of entrapped liquid. With increasing the equivalent strain, the solid grain size decreased and the degree of spheroidization tended to be improved. Furthermore, the rate of liquation was also slightly increased. Increasing the reheating temperature was favorable for obtaining spheroidal semi-solid microstructure and decreasing the probability of coalescence among solid grains. However, prolonging holding time resulted in grain coarsening. The tensile mechanical properties of the thixoformed components were influenced by the amount of equivalent strain during CCDF. Good elongation to fracture (15%) was obtained for thixoformed AM60B magnesium alloy component, with a yield strength of 199.2MPa and a tensile strength of 306.7MPa. [Copyright &y& Elsevier]

Abstract: Semi-solid processing of magnesium alloys is generally based on conventional magnesium-based casting alloys such as Mg–Al series. However, these casting alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Mg–Zn series. In this paper, a ZK60 magnesium alloy with the addition of Y was thixoforged. The semi-solid thermal transformation (SSTT) route and the recrystallisation and partial melting (RAP) route were used to obtain the semi-solid feedstocks for thixoforging. Microstructural evolution during partial remelting was studied at temperatures for times. Tensile mechanical properties of thixoforged components at room temperature were examined. Results show that a fine spheroidal microstructure can be obtained by the RAP route. Compared to the RAP route, the SSTT alloy shows coarsened solid grains with a relatively high proportion of intragranular liquid droplets. With prolonged holding time, the solid grain sizes of the SSTT alloy and the RAP alloy increased. Coalescence was dominant in the SSTT alloy and Ostwald ripening was dominant in the RAP alloy. Thixoforging for the SSTT alloy and the RAP alloy resulted in successful filling of the die. The tensile properties of the thixoforged RAP alloy were satisfactory and exceeded those of the thixoforged SSTT alloy. However, the mechanical properties of both the thixoforged SSTT alloy and the thixoforged RAP alloy decreased with prolonged holding time. [Copyright &y& Elsevier]

Abstract: A new route, near-liquidus forging plus partial remelting, has been developed for obtaining globular microstructures. Firstly, a material is formed by near-liquidus forging for obtaining a fine dendritic microstructure. Globular microstructure can be produced by reheating the material into the semi-solid temperature range for a period of time. In this paper, an AZ91D alloy with the addition of yttrium was prepared by near-liquidus forging. Microstructure evolution during partial remelting was studied at temperatures and for times. Tensile mechanical properties of thixoforged components were also determined. It is shown that the fine dendritic structure firstly evolves into a blocky structure during partial remelting. With prolonged holding time, the blocky structure disintegrates into polygonal solid particles. Prolonging time and increasing temperature promote a faster spheroidization. Good mechanical properties are obtained for the thixoforged AZ91D alloy with the addition of yttrium prepared by near-liquidus forging, with a yield strength of 160.9MPa and a ultimate tensile strength of 301.7MPa and a elongation to fracture of 9.734%. [Copyright &y& Elsevier]

The influence of disordered and ordered body-centered cubic (BCC-β and B2-β′) secondary phases on the mechanical properties and cavitation erosion-corrosion (CE-C) behavior of BCC/B2 strengthened FeNiCrMoAl-based multi-principal element alloy (MPEA) was systematically investigated. An increased β/β′ phases content enhanced the MPEAs' strengths while maintaining good ductility. However, this increases also led to a higher proportion of loosely bound Al 2 O 3 within the passivation film, resulting in a slight reduction in electrochemical corrosion performance. Remarkably, in a NaCl solution, the increased β/β′ phases significantly improved the MPEAs' resistance to CE-C, attributed to the outstanding corrosion resistance and mechanical properties which could withstand elastic strain damage and plastic deformation. • BCC/B2 strengthened Fe 44.2 Ni 27 Cr 23 Mo 1.8 Al 4 MPEAs were fabricated. • Increasing the BCC/B2 phases enhances strength at the expense of ductility. • BCC/B2 phases will increase the defects in the passivation film, degrading corrosion resistance. • BCC/B2 phases can greatly improve CE-C performance due to its strong resistance to deformation. • Large area of softer FCC phase peel off during CE-C is the main cause of volume loss for MPEAs. [ABSTRACT FROM AUTHOR]

In this study, four kinds of heat treatments were performed to obtain a certain amount of retained austenite, which can result in good toughness and low brittleness accompanied with wear resistance of an in situ VC particle reinforced iron-based composite (VCFC). Microstructure, mechanical properties and wear resistance of the samples under heat treatment of QP, QPT, MQP and MQPT were compared. The experimental results indicated that there is a huge difference in microstructure between MQPT and the other heat treatments. High-proportion retained austenite and white net-like precipitates of M7C3 carbide existed in the MQPT-treated sample, but thick M7C3 carbide with brittleness was discovered in the other sample. Thereby, high-proportion retained austenite contributed to its low hardness of 634 HV and high tensile strength of 267 MPa, while a maximum hardness of 705.5 HV and a minimum tensile strength of 205 MPa were exhibited in the QPT-treated sample with a V-rich carbide of high hardness, a Cr-rich carbide of brittleness and a high-proportion martensite. Meanwhile, a phase transformation from retained austenite to martensite could increase the hardness and enhance wear resistance based on the transformation-induced plasticity (TRIP) effect; its wear rate was only 1.83 × 10−6 mm−3/(N·m). However, the wear rates of the samples under QP, QPT and MQP heat treatments increased by 16.4%, 44.3% and 41.0%, respectively. The wear mechanism was a synergistic effect of the adhesive wear mechanism and the abrasive wear mechanism. The adhesive wear mechanism was mainly considered in the MQPT-treated sample to reduce the wear rate attributed to high-proportion retained austenite and the existence of wear debris with a W element on the surface of the wear track. However, the abrasive wear mechanism could exist in the other samples because of a lot of thick, brittle M7C3, thereby resulting in a higher wear rate due to immediate contact between the designed material and the counterpart. [ABSTRACT FROM AUTHOR]

The effects of annealing temperature on the microstructure, mechanical properties, and tribological properties of TiAlSiCN coatings with C contents of 9.24 at.% and 19.45 at.% are systematically investigated. The results show that all coatings maintain cubic structures with strongly preferential orientation of (200) planes, and the microstructure transforms from amorphous embedded in (Ti, Al)(C, N) nanocrystalline to amorphous encapsulated nanocrystalline with increasing C content. Elevating annealing temperature to 800 °C leads to a continuous decline in hardness, whereas the elastic strain resistance H/E increases first and then decreases. Release of H 2 formed by the breaking of the C–H bonds at 400 °C induces a local stress transformation from compressive to tensile. The toughness and hardness decreases dramatically at 600 °C by conversion of sp3 to sp2. The wear mechanisms of the coating against Si 3 N 4 counterballs are adhesive and oxidative wear. The coefficient of friction (COF) and wear rate initially decrease followed by an increase. The coatings with a-C structure exhibit lower COF and the wear process is smoother, but showing higher wear rate. Thus, the annealed TiAlSiCN coatings with preferred C content could improve the mechanical and tribological properties. [ABSTRACT FROM AUTHOR]

As a classic high-entropy alloy system, CoCrFeNiMn is widely investigated. In the present work, we used ZrH2 powders and atomized CoCrFeNiMn powders as raw materials to prepare CoCrFeNiMnZrx (x = 0, 0.2, 0.5, 0.8, 1.0) alloys by mechanical alloying (MA), followed by spark plasma sintering (SPS). During the MA process, a small amount of Zr (x ≤ 0.5) can be completely dissolved into CoCrFeNiMn matrix, when the Zr content is above 0.5, the ZrH2 is excessive. After SPS, CoCrFeNiMn alloy is still as single face-centered cubic (FCC) solid solution, and CoCrFeNiMnZrx (x ≥ 0.2) alloys have two distinct microstructural domains, one is a single FCC phase without Zr, the other is a Zr-rich microstructure composed of FCC phase, B2 phase, Zr2Ni7, and σ phase. The multi-phase microstructures can be attributed to the large lattice strain and negative enthalpy of mixing, caused by the addition of Zr. It is worth noting that two types of nanoprecipitates (body-centered cubic (BCC) phase and Zr2Ni7) are precipitated in the Zr-rich region. These can significantly increase the yield strength of the alloys. [ABSTRACT FROM AUTHOR]

A simple and low-cost method for preparing SiC f /mullite composites with high density, mechanical, and absorbing performance using a vacuum pressure impregnation (VPI) system has been developed. The densification mechanism of the mullite matrix was investigated, and the effects of impregnation pressures on the flexural strength, interfacial bonding strength, and the electromagnetic wave (EMW) absorbing performance of SiC f /mullite composites were also studied. The dense composite was prepared under 3 MPa pressure with a porosity of 6.23 % and median pore diameters (MPDs) of 13.02 nm. The preparation efficiency was improved with the impregnation circles decreased from 20 times to 13 times. The flexural strength of SiC f /mullite composites prepared by VPI is 297 MPa, which is improved 230 % of the one prepared by the traditional vacuum impregnation method. Benefiting from the synergistic effects of appropriate impedance matching and multiple polarization loss, the effective absorption bandwidth (EAB, RL < −10 dB) of the SiC f /mullite composites increases from 2.17 GHz to 2.80 GHz in the X band. This work has a positive application value for the manufacture of high-strength EMW absorbing composites in terms of significantly reducing the preparation cost and cycle duration. [ABSTRACT FROM AUTHOR]

Front Cover: Double network hydrogels (DN gels), consisting of two asymmetric, interpenetrating polymer networks, are considered as the toughest soft materials. This Trend article summarizes the latest important and interesting findings of DN gels, covering new gel structures, functionalities, applications, and future perspectives. Further details can be found in the article by Qiang Chen,* Hong Chen, Lin Zhu, Jie Zheng* on page 1022. [ABSTRACT FROM AUTHOR]

Series of hydrophilic core–shell microgels with cross-linked poly(N-isopropylacrylamide) (PNIPAAm) as core and poly(vinyl amine) (PVAm) as shell are synthesized via surfactant-free emulsion polymerization. Then, the microgels are treated with a small amount of potassium persulfate (KPS) to generate free radicals on the amine nitrogens of PVAm, which subsequently initiate the graft copolymerization of acrylic acid (AA), acryloyloxyethyl trimethyl ammonium chloride (DAC), and acrylamide (AAm) onto microgels to prepare multi-responsive composite hydrogels. The composite hydrogels consist of cross-linked ungrafted polyampholyte chains as the first network and microgels with grafted polyampholyte chains as graft point and second network and show surprising mechanical strength and rapid response rate. The investigation shows the compress strength of composite hydrogels is up to 17–30MPa, which is 60–100 times higher than that of the hydrogel matrix. The composite hydrogel shows reversible switch of transmittance when traveling the lowest critical temperature (LCST) of microgels. When the composite hydrogel swollen in pH 2.86 solution at ambient condition is immersed into the pH 7.00 solution at 45°C, a rapid dynamic shrinking can be observed. And the character time (τ) of shrinking dynamic of composite hydrogel is 251.9min, which is less than that of hydrogel matrix (τ =2273.7min). [Copyright &y& Elsevier]

Doping B/C inhibit O segregation at GB and dramatically improve mechanical properties via GB engineering. [Display omitted] Refractory high-entropy alloys (RHEAs), particularly NbMoTaW RHEAs, exhibit outstanding softening resistance and thermal stability at ultra-high temperatures, but suffer from room-temperature brittleness, which severely limits their processability and thus practical application. In this study, we successfully achieved large plasticity of >10%, along with high strength of >1750 MPa in the NbMoTaW RHEAs via grain boundary engineering with the addition of either metalloid B or C. It was revealed that the room-temperature brittleness of the as-cast NbMoTaW RHEA originates from the grain-boundary segregation of the oxygen contaminant which weakens grain-boundary cohesion. The doped small-sized metalloids preferentially replace oxygen at grain boundaries and promote stronger electronic interaction with the host metals, which effectively alleviates the grain boundary brittleness and changes the fracture morphology from intergranular fracture to transgranular fracture. Our findings not only shed light on the understanding of the embrittlement mechanism of RHEAs in general, but also offer a useful route for ductilization of brittle HEAs. [ABSTRACT FROM AUTHOR]

This study analyzed cavitation erosion (CE) and cavitation erosion-corrosion (CE-C) of single-phase face-centered cubic structured Fe 23.7 Co 23.8 Ni 23.8 Cr 23.7 Mo 5 multi-principal element alloy (MPEA) with varying grain sizes obtained through post-deformation annealing (PDA). The average grain sizes of the samples after annealing at 1100 °C for 60 s, 1150 °C for 60 s, and 1100 °C for 200 s are 4.1 µm, 10.3 µm, and 15.2 µm, respectively. Among them, the 4.1 µm sample exhibits the best combination of high ultimate tensile strength (889 MPa) and large elongation (40.3%), as well as good electrochemical corrosion resistance in NaCl solution. Under the conditions of CE and CE-C for a duration of 10 h, the 4.1 µm specimen exhibits cumulative mass losses of approximately 1.4 mg and 2.6 mg, respectively. In contrast, under identical conditions, the 316 L SS registers cumulative mass losses of approximately 16.7 mg and 24.8 mg, respectively. Due to the excellent mechanical properties and work hardening ability of the 4.1 µm sample, it can effectively resist the plastic deformation caused by cavitation erosion, reducing mass loss. In addition, the stable passivation film enhances its resistance to Cl- destruction, thus demonstrating notable corrosion resistance. Ultimately, under conditions where cavitation erosion and corrosion coexist, these combined properties enable the 4.1 µm sample to exhibit the least mass loss and damage. • Cavitation erosion-corrosion (CE-C) behavior of FeCoNiCrMo 5 MPEA in NaCl solution was studied. • MPEA's tensile strength, corrosion, and CE-C resistance decreased as grain size grown. • Cavitation erosion mechanisms of the MPEA with different grain sizes were elucidated. • Synergistic damage mechanisms of cavitation erosion and corrosion were revealed. [ABSTRACT FROM AUTHOR]

Abstract In this study, a new type of external added nano-sized SiC particles (SiC np for short) and in-situ Mg 2 Si particles reinforced composites, i.e. (1.5 wt% Mg 2 Si+1 wt% SiC np)/Al-Cu composites, has been successfully prepared for the first time, and the microstructure and mechanical properties of the composites are studied. The eutectic Mg 2 Si phase in the Mg 2 Si/Al-Cu composites is refined from short strip with length of about 10 µm to dot shape with diameter of about 2 µm in (Mg 2 Si+SiC np)/Al-Cu composites, which is uniformly distributed inside Al 2 Cu phases precipitated at the grain boundary. The α-Al grains are also significantly refined. It is also first discovered that SiC np can act as nucleus of Mg 2 Si, or be captured by the Mg 2 Si phase during solidification, which promotes the heterogeneous nucleation of the eutectic Mg 2 Si phase to reduce the size of Mg 2 Si phase. The ultimate tensile strength (UTS) and yield strength of (Mg 2 Si+SiC np)/Al-Cu composites are 325 MPa and 210 MPa, which are 3.2% and 28.8% higher than those of Mg 2 Si/Al-Cu composites, respectively. These properties are also improved by 20.4% and 21.4% respectively compared with SiC np /Al-Cu composites, while (Mg 2 Si+SiC np)/Al-Cu composites maintain good ductility. [ABSTRACT FROM AUTHOR]

Abstract AlTiN-Ni coatings with various Ni contents (0–3 at%) were deposited using cathodic arc evaporation. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, a nanohardness tester, scratch-adhesion tester, and cutting tester were used to examine the microstructure, mechanical properties, and cutting performance of the coatings. The AlTiN coatings exhibited a columnar structure, while the AlTiN-Ni coatings exhibited a nanocrystal structure due to the formation of nc-AlTiN/Ni nanocomposite coatings. The nanohardness of the AlTiN-Ni coatings decreased from 26.2 GPa to 20.9 GPa as the Ni content increased from 0 to 3 at%. At an Ni content of 1.5 at%, the coating possessed a high toughness and sufficient adhesion strength; however, these dropped drastically for the AlTiN-Ni coating with 3 at% Ni owing to the presence of amorphous Ni. The results for the Inconel 718 turning indicated that the wear mode is adhesion at the rake face, abrasion and adhesion (built-up edge) at the flank face, and chipping at the cutting edge. Compared to AlTiN-Ni 3 and AlTiN-coated tools, the lifetime of the AlTiN-Ni 1.5 coated tool increased to 160% at a cutting speed of 40 m/min. This was attributed to less adhesion at the rake face and chipping at the cutting edge, due to the nanocrystal structure and higher toughness of the AlTiN-Ni 1.5 coating. [ABSTRACT FROM AUTHOR]

Gelatin/polyacrylamide/graphene oxide nanocomposite double-network hydrogels (Gelatin/PAAm/GO NC-DN gels) were prepared by in situ free radical polymerization. Their structure and properties were systematically characterized by X-ray diffraction (XRD), Raman spectroscopy, swelling experiments, scanning electron microscopy (SEM) and tensile tests. The results reveal that the GO nanosheets are significantly exfoliated in the gel matrix, serving as multi-functional cross-linkers in the NC-DN gels. At an optimal condition, Gelatin/PAAm/GO NC-DN gel demonstrates an excellent mechanical properties of an elastic modulus ( E ) of 187.3 kPa, a fractured stress ( σ f ) of 0.324 MPa), a fractured strain ( ε f ) of 45.5 mm/mm and a fractured energy ( W ) of 10.18 MJ/m 3 . More interestingly, the gels show a large hysteresis loop, softening phenomenon and self-recovery properties. This work deepens the understandings of the effect of nanomaterials on the mechanical properties of DN gels. [ABSTRACT FROM AUTHOR]

In the present work, in-situ Al 3 Ti/2024Al composites with different amount of Al 3 Ti reinforcements were fabricated by ultrasonic casting method. The effects of solution and subsequent aging treatment on the microstructures and mechanical properties were studied. The results show that solution at 500 °C for 6 h is suitable for in-situ Al 3 Ti/2024Al composites with mass fractions of reinforcements between 4 wt% and 16 wt%. The aging kinetics of Al 3 Ti/2024Al composites was promoted by the Al 3 Ti reinforcements. When the mass fraction of Al 3 Ti is increased from 0% to 16%, the peak hardness is increased by 20.3%, and the time required to reach the peak hardness is shortened by 66.7%. The microstructures of peak-aged Al 3 Ti/2024Al composites consist of equiaxed α-Al grains and evenly distributed reinforcing particles. As the mass fraction of Al 3 Ti increasing, the compression and tensile strengths were both increased gradually at the sacrifice of plasticity. [ABSTRACT FROM AUTHOR]