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The solidification characteristics of commercially pure aluminum with and without vibration were investigated using experiments and numerical simulation methods. The results showed that the vibration condition is beneficial to the filling flow. The changes of melt flow and temperature field were studied and compared with those obtained without a mechanical vibration field. The existence of the mechanical force causes the melt velocity to be accompanied by abrupt fluctuations at different positions of the melt. However, the ending time of vibration solidification is slightly longer than that without applying mechanical vibration field. The application of mechanical vibration significantly refines the grain size, thereby increasing tensile strength and elongation. With the increase in vibration frequency, the solidification structure of the alloy is refined and then coarsened. It is, therefore, found that the optimal mechanical vibration frequency is 30 Hz. The present study can provide guidance for engineering practice in the vibration field. [ABSTRACT FROM AUTHOR]

The microstructure of ferromagnetic phase usually has an essential influence on the soft magnetic properties. In the present study, the effects of Si element, cold deformation and heat treatment on the microstructure of Fe-rich phase and soft magnetic properties of Cu–10Fe alloy were investigated. The results showed that the addition of Si caused more formation of α-Fe solid solution, as well as its morphology transformation from developed dendrites to cellular dendrites. The saturation magnetization thus increased to 17.28 emu/g and the coercivity decreased to 15.75 Oe. After rolling deformation and aging treatment, Fe-rich phase was further precipitated and generated the 100 preferred orientation, leading to the improvement of saturation magnetization to 18.39 emu/g, increased by 29.8% compared with the as-cast Cu–10Fe alloy. While after rolling deformation and aging treatment, the coercivity was 12.17 Oe, significantly reduced by 55.7%. The refinement of secondary precipitated Cu-rich phase and the decrease of dislocation density were responsible for the improvement of coercivity. [ABSTRACT FROM AUTHOR]

CoCrFeNi high-entropy alloy (HEA) exhibits excellent mechanical properties but relatively poor wear resistance. In particular, when the load reaches a certain level and the deformation mechanism of the CoCrFeNi HEA changes, the formation of shear bands leads to a significant increase in wear rate. Although numerous studies have been conducted on alloying strategies to improve the wear resistance of alloys, there is still limited research on the influence of deformation mechanism adjustment on wear resistance. Therefore, in order to fill this research gap, this study aims to use boron doping to regulate the deformation mechanism and successfully improve the wear resistance of CoCrFeNi HEA by 35 times. By observing the subsurface microstructure, the mechanism behind the significant improvement in wear resistance was further revealed. The results indicate that the reduction of shear bands and the formation of nanostructured mixed layers significantly improve wear resistance. The proposed strategy of boron doping to change the deformation mechanism and improve wear resistance is expected to provide new enlightenment for the development of wear-resistant HEAs. [ABSTRACT FROM AUTHOR]

In the present study, the effect of pulsed magnetic field (PMF) on the solidification structure of commercial purity Al during unidirectional solidification was investigated through a series of experiments. The results show that columnar grains are formed without PMF, whereas a refined equiaxed grain layer with a smooth interface inside the large columnar dendrites is formed by controlling application of PMF. The nucleation sites can be ascribed to the direct heterogeneous nucleation in the bulk liquid and the detachment of grain nucleus from the mold wall. With increasing nucleation sites, the blockage of the columnar front and columnar-to-equiaxed transition occurs based on a threshold value of the volumetric fraction of equiaxed grains, which can be proven by the delay of equiaxed grain formation after switching on the PMF. After the magnetic field is switched off, the nucleation sites are full of liquid metal and settle down along the direction of gravity. At this time, the temperature gradient of the liquid is rebuilt, and finally a three-layer solidified structure is formed. The study is beneficial to deepen the understanding of solidification structure evolution of metals with a forced melt flow and temperature field. [ABSTRACT FROM AUTHOR]

Eutectic high‐entropy alloys (EHEAs), as an important branch of high‐entropy alloys (HEAs), have become hotpots in the materials field due to the excellent combination of mechanical properties and casting liquidity. However, designing of EHEAs containing nonmetallic elements has been rarely reported. Herein, a new strategy to design EHEAs containing nonmetallic elements by introducing an idealized mode of A‐(M + N) and using computer‐aided thermodynamic calculations is proposed. Based on this strategy, four new EHEAs, namely, CoFeNi2–Ti0.48Si0.8, CoCrNi2–V0.86B0.43, CoCrFeNi2–V0.89B0.45Si0.15, and CoCrNi2–MoC0.6, are designed and prepared. The CoFeNi2–Ti0.48Si0.8 and CoCrNi2–MoC0.6 EHEAs are composed of face‐centered‐cubic (FCC) + M16Ti6Si7‐type silicide and FCC + M23C6 + M6C‐type carbide, respectively. The CoCrNi2‐V0.86B0.43 and CoCrFeNi2‐V0.89B0.45Si0.15 EHEAs exhibit the same eutectic microstructure as FCC + M3B2‐type boride. The synthesized EHEAs containing nonmetallic elements show excellent mechanical properties. The experimental result indicates that this strategy can provide a feasible and effective way to develop new EHEAs with nonmetallic elements. [ABSTRACT FROM AUTHOR]

A novel series of Fe8.25CoCrNiMnNb0.1Mox (x = 0, 0.05, 0.1 and 0.15, mole ratio) multi-component alloys (MCAs) were designed and prepared based on the design of high-entropy alloys. The effects of Mo on the microstructure and mechanical properties of MCAs were investigated. All the MCAs consisted of face-centered-cubic (FCC), body-centered cubic, and eutectic phase of FCC + Laves multiphase structures with excellent mechanical properties, which originated from the second-phase and solid solution strengthening. In particular, MCAs having 0-0.15 Mo showed that the tensile strength increased from 556.2 to 678.1 MPa with an excellent elongation to fracture of 58-40%, while the hardness increased from 170.8 to 202.5 HV. The novel series of MCAs significantly reduced the cost of raw material and widened the processing window, which increased the potential for industrial applications. [ABSTRACT FROM AUTHOR]

Laminated Cu–Pb–Sn/Steel composites (C/SC) with Pb-rich secondary phases (SPs) in different morphology were prepared by solid–liquid continuous casting compositing (S-LC). SPs transform from network to rod-like to abnormally coarsening morphology with casting temperatures increasing from 1473 K to 1513 K to 1533 K. The prepared C/SC possesses a high-quality interface and high bonding strength due to the existence of the Cu/Fe interdiffusion layer with a thickness of about 0.75 μm. The thickness calculated by CALPHAD is in the range of 0.38 to 1.35 μm which is consistent with experimental results. The mechanical properties of C/SC present a high correlation with the morphology of SPs. C/SC with network and rod-like SPs, respectively, shows the lowest and highest plasticity and carrying capacity. Finite element analysis (FEA) was conducted to simulate the plastic deformation of C/SC. By comparing the experiments with FEA results, the network SPs with high continuity were proven to significantly decrease the tensile strength and elongation of Cu–Pb–Sn alloy layer of C/SC by splitting the matrix. C/SC with rod-like SPs presents the highest mechanical performance due to the minimal damage to matrix. [ABSTRACT FROM AUTHOR]

Recently, eutectic high-entropy alloys (EHEAs) have attracted considerable attention owing to their outstanding mechanical properties and excellent castability. However, EHEA design remains a huge challenge. Traditional grouping design strategies excessively depend on the reported alloy composition. Meanwhile, the quantitative boundary conditions of grouping strategies remain unclear. This work proposes a grouping strategy via the d-orbit energy level ( Δ M d i j ) to design EHEAs. The Δ M d i j model was an extension of the grouping strategy, which did not require the existing alloy composition and provided a clear boundary condition for grouping the component elements. Accordingly, (CoFe2NiV0.5Mo0.2)91Zr9 EHEA with nanostructured fully eutectic morphology was designed and prepared by direct solidification. This work provided a perspective to advance the understanding of grouping design strategies for EHEAs and make it possible to design the composition of EHEAs on a large scale. [ABSTRACT FROM AUTHOR]

A novel Al0.5V0.1FeCrMnNi0.9 high-entropy alloy was designed to achieve enhanced strength and plasticity. The as-cast Al0.5V0.1FeCrMnNi0.9 alloy shows a typical dendritic microstructure consisting of a body-centered cubic-structured matrix phase and a B2-structured nanoprecipitate phase. Nanoprecipitates are homogeneous and dispersed in the matrix. The as-cast Al0.5V0.1FeCrMnNi0.9 alloy exhibits a compressive yield strength of 1.104 GPa, a fracture strength of 2.926 GPa, and a fracture strain of 45.7%. The product of strength and plasticity of this alloy is 133.72 GPa%, which is superior to that of most of the reported high-entropy alloys. The strengthening mechanisms were evaluated in detail, which indicates that the coherent precipitation enhancement contributes to the unusually high strength and plasticity. [ABSTRACT FROM AUTHOR]

Refractory high‐entropy alloys (RHEAs) with excellent high‐temperature performance are attractive for high‐temperature structural applications. However, many RHEAs suffer from high density and poor room temperature (RT) malleability. Herein, the effects of Ti and Nb contents on the phase equilibrium and mechanical properties of HfZrVTaMoWTixNby RHEAs are studied to achieve unique balanced properties in a wide temperature range. With the increase of Ti or Nb content, the Laves phase precipitation is suppressed and RT malleability is improved. Particularly, the HfZrVTaMoWTi2Nb2 RHEA without Laves precipitates exhibits a high yield strength of 1.7 GPa and a compressive strain of ∼30% at RT. Moreover, it retains a high systemic yield strength of 31 MPa cm3 g−1 at 1200 °C, which is nearly three times that of HfZrTaTiNb and nearly equal to that of MoWTaNb, suggesting its potential applicability at elevated temperatures. [ABSTRACT FROM AUTHOR]

A CoCrCuNiAl0.5 high-entropy alloy (HEA) was prepared by spark plasma sintering (SPS). The effect of plasma transferred arc (PTA) remelting on the microstructures and properties of the SPS-ed HEA was studied. The results showed that, after PTA remelting, the microstructures transformed from randomly-oriented equiaxed grains to dendrites with a directional solidified morphology. The coarse plate-like precipitates (~ 130 nm in diameter and ~ 20 nm in thickness) containing ordered L12 and disordered FCC structures inside the matrix grains were replaced by the disordered FCC spherical Cu-rich precipitates with several nanometers within the dendritic matrix. In the intergranular region, the size of the L12 cubic precipitates was decreased from ~ 55 nm to ~ 2 nm, and dislocations and lattice distortions were also observed. In addition, the brittle B2 phase was disappeared, and the extent of Cu segregation was decreased in the interdendritic region. The SPS-ed sample has a compressive yield strength of 913.8 MPa and a fracture strain of 21.7%. However, the PTA remelted sample exhibits a much higher fracture strain (> 70%, without fracture) and an appreciable yield strength of 739.4 MPa, which indicates an excellent balance between strength and ductility was achieved after PTA remelting. Furthermore, the corrosion resistance of the PTA remelted sample was higher than that of the SPS-ed sample, which was mainly due to the decreased elemental segregation, and the reduced sizes and types of the precipitates. [ABSTRACT FROM AUTHOR]

In aeroengines, thermal barrier coatings (TBCs) are usually utilized to protect the hot components from hot gases. The ability to predict the TBC failure is crucial to avoid economic losses. In this study, plasma-sprayed 8 wt.% yttria-stabilized zirconia (YSZ) coatings were subjected to corrosion by calcium–magnesium–aluminosilicate (CMAS, 33CaO–9MgO–13Al2O3–45SiO2) glass at 1250 °C. After the test, two morphologies were observed on the coating surface. At the sample edges, the coating underwent over-sintering because of the locally high temperature: the molten glass easily penetrated the YSZ layer and reacted with it; and iron spinel was detected on the surface. In the sample central region submitted to a relatively lower temperature, a dense layer consisting of both CMAS glass and YSZ was formed. The analysis of the self-luminescence of the YSZ coating after corrosion revealed the presence of sintered regions on the coating surface, which increased as the corrosion temperature increased. This came with a decrease in the coating luminescence. This study shows that the self-luminescence properties can be used to monitor the degree of corrosion and predict the failure of the coating. [ABSTRACT FROM AUTHOR]

The functionally gradient material (FGM), consisting of pure Al outer layer and Al–B4C inner layer, was fabricated by semi-continuous casting with subsequent hot rolling. B4C particles of four different sizes (11, 26, 53, and 75 μm) were used as the reinforcement phase. The effect of B4C size on the microstructure and mechanical properties of the FGM composites was analyzed. Obtained results show that the B4C particles are uniformly distributed in the inner layer. With the increase of B4C particle size, the Brinell hardness of these FGMs increases, but the impact properties decrease. [ABSTRACT FROM AUTHOR]

The solidification characteristics and segregation behavior of Cu-15Ni-8Sn alloy were systematically investigated in the present study. The solidification characteristics were revealed with the assistance of a solidification quenching experiment, DTA analysis and Scheil simulation. The solidification microstructure of Cu-15Ni-8Sn alloy was characterized by SEM, and the results indicated that the as-cast microstructure of Cu-15Ni-8Sn alloy mainly consists of Sn-depleted α-Cu(Ni,Sn) matrix, Sn-rich γ phase and lamellar (α + γ) structure. It has been demonstrated that the solidification process begins with the nucleation and growth of primary Sn-depleted α1 phase ( L → α 1 at 1114 °C) and terminates with the divorced eutectic reaction ( L 2 → α 2 + γ at 868 °C). During the subsequent cooling process, the discontinuous precipitation ( α 2 → α 1 + γ ) takes place in the temperature range from about 700 °C to 600 °C. In addition, the macrosegregation behavior of Sn in Cu-15Ni-8Sn alloy was investigated by adopting vertical unidirectional solidification and measuring the cooling curves at different positions. The results indicated that an inverse macrosegregation of Sn solute exists in the as-prepared ingot, which mainly segregates at the chill surface of the alloy ingot. Namely, the Sn content is higher than 8 wt pct at the chill surface and about 8 wt pct inside the ingot for Cu-15Ni-8Sn alloy. [ABSTRACT FROM AUTHOR]

Silicate-based glass powder was prepared and doped into commercially used Al2O3-13 wt.%TiO2 powder (AT13) for plasma spraying. The morphology and phase structure of the glass-doped AT13 coating (G-AT13) were characterized by scanning electron microscopy/energy-dispersive spectroscopy and x-ray diffraction analysis. The results revealed that the glass particles were able to fully spread to adapt to the roughness of the ceramic sheet layer and fill the pores between the ceramic particles, thereby reducing defects such as pores and microcracks inside the coating layer. Compared with the AT13 coating, the G-AT13 coating was more compact with lower porosity of 4.2% and higher microhardness of 1938 HV. After 2400 h of immersion corrosion in 3.5 wt.% NaCl solution, the AT13 coatings displayed severe corrosion with cracks and rust on the surface, whereas the G-AT13 coating only exhibited a small amount of rust on the surface. Electrochemical measurements (Tafel polarization and electrochemical impedance spectroscopy) also indicated that the G-AT13 coating possessed higher corrosion resistance than the pure AT13 coating. Doping of glass into the ceramic coatings therefore improved the long-term corrosion resistance of the coatings. [ABSTRACT FROM AUTHOR]

Strength and ductility are the two most essential properties for copper alloys which are commonly used as structural materials. However, these properties are often mutually exclusive and seldom improved simultaneously in the samples fabricated through plastic deformation. For example, room temperature rolling (RTR) samples with a large deformation amount usually exhibit high strength but poor ductility. The present study provides an effective strategy for obtaining satisfactory mechanical properties in a Cu-30Zn brass. Compared with RTR sample with a large deformation amount (90%), a desired and outstanding combination of high strength and superior ductility can be achieved in a low deformation (70%) sample fabricated through ultra-low temperature rolling (UTR). The average tensile strength of 90% deformation RTR sample is 641.7 MPa, whereas that of 70% deformation UTR sample is 695.4 MPa. The average elongation of the 90% deformation RTR sample is only 3.7%. By contrast, the average elongation of 70% deformation UTR sample is 7.2%. In the meantime, the average yield strength of 70% deformation UTR sample is higher than that of 90% deformation RTR sample, which are 598.2 and 561.7 MPa, respectively. Large proportions of ultrafine grains and nanometer-scale deformation twins are responsible for the excellent mechanical properties of 70% deformation UTR sample. This effective method is vital for industry production to simultaneously obtain high strength and superior ductility in Cu-30Zn brass and may be also suitable for other copper alloys. [ABSTRACT FROM AUTHOR]

In this work, the alloying effects of Ta element on the microstructure evolution and mechanical properties of CoCu0.5FeNiTax (x = 0-0.6 at.%) high-entropy alloys were studied. The microstructure changed from single solid solution to hypoeutectic, then to eutectic, and finally to hypereutectic with the increase in Ta content, which is because Ta element facilitates the Laves phase to form. The volume fraction of hard and brittle Laves phase increases with the Ta content, which increases the yield strength, Vickers hardness and theoretical density but decreases the plastic strain. The CoCu0.5FeNiTa0.1 alloy with a single FCC solid solution structure shows the optimal balance between density and ductility. The theoretical density and tensile fracture strain can reach 8.94 g/cm3 and 36.3%, respectively. [ABSTRACT FROM AUTHOR]

To enhance the red emission efficiency of Eu3+ complexes, [Eu/Tbx(BPA)3phen] (BPA = bisphenol A, phen = 1,10-phenanthroline) is designed and synthesized. The complexes are characterized fully and their luminescence properties are evaluated. Co-fluorescence is detected in the Eu/Tbx(BPA)3phen complexes, and the existence of Tb3+ enhances the luminescence intensity of the central Eu3+ because of the intramolecular energy transfer from the 5D4 level of Tb3+ to the 5D0 level of Eu3+. The luminescence intensity of europium ions at 615 nm is the highest for Eu/Tb1(BPA)3phen. To improve the thermal stabilities and mechanical properties of pure complexes, Eu/Tb1(BPA)3phen/PAN (PAN = polyacrylonitrile) is used to fabricate fibres by electrospinning. Compared with Eu/Tb1(BPA)3phen (τ = 1.1087 ms), the fibres have a longer fluorescence lifetime of 1.533 ms. The fibres also retain a high quantum yield of 47.16%. Thus, the flexible luminescent fibres have potential applications in many fields. [ABSTRACT FROM AUTHOR]

Reinforcement particle size is very important for the performance of metal ceramic composites. This work studied the influence of B4C particle size on the mechanical properties of Al matrix layered composites. These composites were fabricated using a simplified semicontinuous casting and hot-rolling process. To obtain an optimized filling structure of particles, Horsfield filling principle was applied to determine the size and mass fraction of B4C particles. Four sizes of B4C particles were used with various combinations. The results showed that with the increase of the B4C particle size and fine B4C mass fraction, the hardness of the composites decreases whereas the impact strength and ultimate tensile strength increase. The residual stress at interface should be responsible for the variation in properties. Besides, the interparticle distance also contributes to the change in impact strength and ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Plasma sprayed NiCrAl/Al2O3-13wt.%TiO2coating was fabricated and annealed at 300–900 °C in air atmosphere. The Elastic modulus (E), micro-hardness (HV) and fracture toughness (Kca) were evaluated by Vickers Indentation Fracture technique. The microstructure was studied by scanning electron microscopy. It can be concluded that with the increasing of annealing temperature,EandHVat the interface of Substrate/Bond layer (S/B) are firstly increased and retain the highest value at 600 °C then decreased with higher annealing temperatures due to the phase transformation.Eof the ceramic coating rised initially with annealing temperature increasing, reached the highest value at 400 °C, and then decreased with the further increasing of the temperature. TheKcaof the S/B interface firstly increased as the heating temperature increasing, confirming the crack initiation resistance increasing after annealing with the temperature below 700 °C. However, theKcadecreased for further annealing temperature, even lower than that of the as-sprayed coating. Thereby, a proper annealing temperature can improve the mechanical properties of the coating since the coating becomes denser, ceramic lamellar structure becomes ambiguous and cracks are partially healed. [ABSTRACT FROM PUBLISHER]

The effects of C element on the microstructure and properties of CoCrFeNiC high entropy alloys ( denoted the atomic fraction of C element at 0, 0.05, 0.1, 0.2, 0.3, and 0.5) were investigated. The equal molar CoCrFeNi alloy with FCC structure exhibits high ductility but weak strength. With the addition of C element, both the hardness and strength of the CoCrFeNiC high entropy alloys increase as well as the wear resistance. The solution strengthening and the formation of hard carbide phase are the main factor for the improved strength, hardness and wear resistance of CoCrFeNiC high entropy alloys. [ABSTRACT FROM AUTHOR]

Pulsed magnetic field (PMF) was successfully applied during direct chill (DC) casting of 6063 Al alloy. The effect of PMF on the solidification structure and mechanical properties was investigated. The results indicated that the coarse equiaxed grain turns into homogeneous and refined equiaxed grain under the effect of PMF, and the grain refinement effect increases with increasing the input current in the study. This can be attributed to the reduced temperature gradient in the melt and enhanced heterogeneous nucleation caused by forced convection, based on the simulation results of Lorenz force, flow field, and temperature field during DC casting under PMF. The application of PMF can also efficiently reduce the macro- and microsegregations of Mg and Si elements, which are beneficial to the uniformly dispersed precipitation of MgSi phase after T6 treatment, resulting in a significant enhancement of strength and hardness. The best mechanical properties of the 6063 Al alloy are achieved under PMF with an input current of 500 A, exhibiting the increments of 35.6% in hardness, 42.2% in ultimate tensile strength, and 30.6% in elongation, respectively. This study may offer a promising method for industrial preparation of high-quality alloys by DC casting. [ABSTRACT FROM AUTHOR]

An innovative horizontal continuous casting method was developed and successfully used to prepare copper-clad aluminum (CCA) rods with a diameter of 85 mm and a sheath thickness of 16 mm. The solidification structure and element distribution near the interface of the CCA ingots were investigated by means of a scanning electron microscope, an energy dispersive spectrometer, and an electron probe X-ray microanalyzer. The results showed that the proposed process can lead to a good metallurgical bond between Cu and Al. The interface between Cu and Al was a multilayered structure with a thickness of 200 μm, consisting of CuAl, CuAl, α-Al/CuAl eutectic, and α-Al + α-Al/CuAl eutectic layers from the Cu side to the Al side. The mean tensile-shear strength of the CCA sample was 45 MPa, which fulfills the requirements for the further extrusion process. The bonding and diffusion mechanisms are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Al-5Ti-0.2C, Al-0.8Ti-0.2C, Al-8Ti-2C, and Al-10Ti master alloys were prepared and used to investigate the influence of excess Ti on the growth of TiC particles and its ability to nucleate Al-grains. The results of a microstructure analysis of TiC-containing alloys and refined CPAl were interrelated to the results of a refinement test. It was found that the presence of excess Ti is essential at the stage of master alloy preparation, as it facilitates the growth and uniform distribution of TiC within the structure. In Al-5Ti-0.2C alloy containing excess Ti, carbide particles grow faster and to a higher extent (from 0.29 μm to 0.44 μm) compared to Al-0.8Ti-0.2C alloy produced without excess Ti (from 0.29 μm to 0.32 μm). The results support the 'Ti-transition zone theory' as the mechanism of grain refinement by TiC-containing master alloys. The refinement performance of Al-5Ti-0.2C is superior compared to the one achieved by adding Al-8Ti-2C and Al-10Ti master alloys in corresponding concentrations. For the TiC particles to become favourable nucleating sites, they must undergo certain interaction with excess Ti at the stage of master alloy preparation. [ABSTRACT FROM AUTHOR]

When Al-Ti-C master alloys are produced via the conventional Self-propagating High-temperature Synthesis (SHS), the reduction of production temperature below 1523 K leads to the drastic deterioration of the refiner efficacy. In the present work, a simple yet effective way to improve the combustion process for low TiC-containing refiners is proposed. The SHS reaction was performed to obtain Al-10TiC slurry first, which subsequently was mixed with Al-Ti melt to obtain Al-5Ti-0.2C master alloy. By means of the proposed method, the process temperature was lowered to 1323 K. According to the results, in the case of improved SHS approach, the Al temperature after the onset of reaction increases by 90-100 K more than in the case of conventional preparation route, providing better kinetic conditions for TiC formation. As a result, at 1323 K production temperature, the average carbide size increases by 100% as compared to the conventionally produced refiner, which is claimed to be a reason for the improved refining performance of master alloy. [ABSTRACT FROM AUTHOR]

MnSi is an attractive dispersion in the special brass, owing to its high hardness and high wear resistance. In the present study, synchrotron X-ray radiography and rapid cooling were applied to investigate the formation mechanism of MnSi phase in the MBA-2 brass alloy. The primary MnSi phase is proved to exist stably in the alloy melt and nucleate from the melt at temperatures above 1373 K (1100 °C). In addition, the precipitation mechanism of MnSi phase is addressed systematically by the isothermal heat treatment. The MnSi particles are observed to precipitate from the matrix at temperatures above 1023 K (750 °C), and a crystallographic orientation relationship is found between the precipitated MnSi particle and β phase: $$ (110)_{\beta } //(1\overline{1} 00)_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} $$ and $$ [\overline{1} 11]_{\beta } //[11\overline{2} \overline{2} ]_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} $$ . However, the precipitation of MnSi phase is thermodynamically inhibited at lower temperatures, which can be ascribed to the increase in the Gibbs free energy of formation of MnSi with decreasing the temperature. [ABSTRACT FROM AUTHOR]

The high-entropy alloy (HEA) coatings have received considerable attentions owing to their unique structures and properties caused by the quick solidification. In this work, the CoFeNiVNb and CoFeNiVNb HEAs which show fully eutectic and hypereutectic microstructures in their casting samples were laser cladded on 304 stainless steel substrate with laser power of 1400, 1600, and 1800 W. Results show that the HEA coatings are composed of the FCC solid solution phase and the FeNb-type Laves phase. The cladding zones of the CoFeNiVNb and CoFeNiVNb coatings show cellular dendritic crystals, while the bonding zones show directional columnar crystals. Compared to the 304 stainless steel substrate, the HEA coatings show better wear resistance because of the combination of the hard FeNb-type Laves phase and the ductile FCC solid solution matrix. Moreover, the HEA coatings with power of 1600 W show the best wear resistance attributing to the maximum volume fraction of the hard FeNb-type Laves phase. [ABSTRACT FROM AUTHOR]

CrFeNiVW and CrFeNiVW ( x = 0.25, 0.5, 0.75, and 1.0) high-entropy alloys were prepared by vacuum arc melting. The effects of W element on the microstructures and mechanical properties of these alloys were investigated. The experimental results indicated that the CrFeNiVW alloys were composed of σ, FCC, and BCC phases. Although the microstructures of the CrFeNiVW alloys were still constituted by FCC, BCC, and σ phases, the volume fraction of the FCC phase increased significantly. Dendrite morphology was also observed in the CrFeNiVW alloys. With the addition of W element, the hardness of the CrFeNiVW alloys declined from 869 to 633 HV, while the hardness of the CrFeNiVW alloys increased from 226 to 305 HV. Moreover, the CrFeNiVW alloys exhibited better compressive ductility than the CrFeNiVW alloys. This study was the first known incidence in which the FCC phase increased in the HEAs with a decrease of the valence electron concentration (VEC) value (i.e., the FCC phase of the CrFeNiVW alloys increased with the addition of the BCC-structured W elements). [ABSTRACT FROM AUTHOR]

The influences of added Fe element on the microstructures and properties of AlCoCrFeNi high-entropy alloys ( x denoted the atomic fraction of Fe element at 0.2, 0.4, 0.6, 0.8, 1.2, 1.4, 1.6, 1.8, and 2.0) were investigated. When x = 0.2, the alloy exhibited dendrites morphology, but as the Fe content increased, the AlCoCrFeNi HEAs transformed to equiaxed grains morphology. Inside the equiaxed grains and dendritic grains, spinoidal decomposition microstructure could be clearly observed. The microstructures changed from CrNi + B2 + BCC structures to B2 + BCC mixed structures as x exceeded 0.6, the hardness declined from HV637.2 to HV460.2, and the compressive fracture strength showed a slight decrease, whereas the plastic property showed a distinct improvement with the addition of Fe element. The maximum compression strength was 2335MPa when x = 0.2, and the maximum compression ratio was 36% when x = 2.0. The alloys transformed from paramagnetic to ferromagnetic as the content of Fe element increased, and all of the alloys exhibited soft magnetic behaviors. [ABSTRACT FROM AUTHOR]

Casting and hot rolling are proposed to verify a semi-continuous casting and hot rolling process to produce a three-layer Al/Al-B C metal-cermet composite. The outer layer is pure Al, the inner layer is Al matrix composite reinforced with B C particles (the mass fraction of Al and B C are 62.36 and 37.64%, respectively). The results show that the reinforced particles are distributed in the inner layer homogeneously, and both layers are sintered together with no pores or flaws. The clad ratios of the composites of 26, 5, 3, and 1 mm are 50.28, 54.67, 61.23, and 57.46%, respectively. The Vickers hardness varies from 46 HV for the outer pure aluminum layer to 158 HV for the inner composite layer in 3 mm specimen, indicating totally different properties in different layers. [ABSTRACT FROM AUTHOR]

The bulk AlCrFeNiMo high-entropy alloy was successfully prepared by vacuum medium frequency induction melting. The effects of electromagnetic field on microstructure and properties were investigated. The alloy possessed a mixed structure of B2 and BCC, and the phase types were not changed by the electromagnetic field treatment. The microstructure exhibited typical lamellar eutectic cell and rod eutectic cell structures. These eutectic cell structures were constituted by the AlNi-type intermetallic compound and the FeCr-type solid solution. With the increase of electromagnetic field intensity, the hardness increases, while the compressive fracture strength and fracture strain of the alloy first increases and then decreases. The alloy with 15 mT electromagnetic field has the largest fracture strength 2282.3 MPa, yield strength 1160.5 MPa, and fracture strain 0.29. The alloy shows typical ferromagnetic behavior, and the homogenized lamellar eutectic cell microstructure significantly decreased the specific saturation magnetizations. [ABSTRACT FROM AUTHOR]

A series of AlCrFeNiMo ( x = 0 to 2.0 at.%) high-entropy alloys coatings was synthesized on stainless steel by laser cladding. The effect of Mo content on the microstructures and mechanical properties of AlCrFeNiMo coatings was studied. The results show that the laser clad layer consists of the cladding zone, bonding zone, and heat-affected zone. The AlCrFeNiMo coatings are composed of two simple body-center cubic phases and the cladding zone is mainly composed of equiaxed grains. When the content of Mo reaches 2 at.%, a eutectic structure is found in the interdendritic regions. The surface microhardness of the AlCrFeNiMo coating is 678 HV, which is about three times higher than that of the substrate (243 HV). Compared with stainless steel, the wear resistance of the coatings has been improved greatly. The wear mass loss of the AlCrFeNiMo alloy is 9.8 mg, which is much less than that of the substrate (18.9 mg) and its wear scar width is the lowest among the AlCrFeNiMo coatings, indicating that the wear resistance of the AlCrFeNiMo is the best. [ABSTRACT FROM AUTHOR]

The three dimensional (3D) microstructures of Al-Bi alloys with different grain refiners (Al-5Ti-B, Al-3B and Al-3Ti) have been studied using synchrotron X-ray microtomography. The relationships between the microstructures and the corresponding wear behavior are verified through the friction and wear tests. The worn surfaces of the samples with grain refiners tested under 15 and 60 N loads are analyzed using Scanning Electron Microscopy (SEM). The results indicate that the addition of grain refiners is beneficial to the size and distribution of the Bi-rich particles in Al-Bi alloys. Compared with Al-5Ti-B and Al-3B grain refiners, the Bi-rich particles are more uniformly distributed and spherical with finer size with the addition of Al-3Ti grain refiner. The refinement renders the Al-20wt%Bi alloy refined by Al-3Ti the superior wear resistance with respect to those refined by Al-5Ti-B and Al-3B grain refiners, corresponding to the microstructures with fine and uniformly distributed Bi-rich particles in the Al matrix. [ABSTRACT FROM AUTHOR]

Copper-chromium matrix composites reinforced by TiB particles were prepared by in situ reaction between titanium and copper-boron alloy in the melt. The microstructures, mechanical, and electrical properties of the composite were investigated under as-cast and aging conditions. The results indicate that the TiB particles are formed by in situ reaction in matrix. The addition of TiB in composite reduces the segregation degree of Cr particles in matrix and inhibits the coarsening of Cr particles at high aging temperature. High hardness of Cu-Cr-TiB composite is achieved due to the multiple hardening mechanisms, which are in situ TiB particles hardening and precipitation hardening from Cr particles. The wear resistance of composite presents a dramatic improvement due to the formation of TiB particles, and TiB particles have significant effect on wear mechanism of Cu-Cr-TiB composite. The conductivity of composite is lower than that of Cu-Cr alloy, which is attributed to higher resistivity of TiB particles and the incremental interface scattering caused by TiB particles. But the composites with high TiB content still have considerable conductivity after aging. [ABSTRACT FROM AUTHOR]

A series of CoFeNiVNb ( x = 0-1) high-entropy alloys (HEAs) were synthesized to investigate the alloying effect of the Nb element on the microstructures and properties. It was found that the microstructures change from initial single-phase FCC solid solutions ( x = 0), to a hypoeutectic microstructure (0 < x < 0.75), then to a fully eutectic microstructure ( x = 0.75), and finally to a hypereutectic microstructure (0.75 < x < 1). The eutectic microstructure consists of the FCC solid solution phase and the FeNb-type Laves phase. Nb0 ( x = 0) and Nb02 ( x = 0.2) alloys exhibit excellent ductility, the compressive plastic elongation of which can reach up to 80 % without fracture. With increasing Nb content, increased brittle Laves phase leads to the decrease of the plastic strain and the increase of the yield strength, and the Vickers hardness shows an approximately linear increase from HV 133.4 to HV 687.7. Besides, the CoFeNiVNb HEAs exhibit excellent soft magnetic behavior, in which the Nb0 alloy shows the maximum saturation magnetization ( M) of 70.33 emu/g, and minimum coercivity ( H) of 1.62 Oe. [ABSTRACT FROM AUTHOR]

To produce a high quality semisolid slurry that consists of fine primary particles uniformly suspended in the liquid matrix for rheoforming, chemical refining and electromagnetic or mechanical stirring are the two methods commonly used. But these two methods either contaminate the melt or incur high cost. In this study, the damper cooling tube (DCT) method was designed to prepare semisolid slurry of A356 aluminum alloy, and was compared with the low superheat casting (LSC) method - a conventional process used to produce casting slab with equiaxed dendrite microstructure for thixoforming route. A series of comparative experiments were performed at the pouring temperatures of 650 °C, 638 °C and 622 °C. Metallographic observations of the casting samples were carried out using an optical electron microscope with image analysis software. Results show that the microstructure of semisolid slurry produced by the DCT process consists of spherical primary α-Al grains, while equiaxed grains microstructure is found in the LSC process. The lower the pouring temperature, the smaller the grain size and the rounder the grain morphology in both methods. The copious nucleation, which could be generated in the DCT, owing to the cooling and stirring effect, is the key to producing high quality semisolid slurry. DCT method could produce rounder and smaller α-Al grains, which are suitable for semisolid processing; and the equivalent grain size is no more than 60 μm when the pouring temperature is 622 °C. [ABSTRACT FROM AUTHOR]

This study aims at understanding the effects of rotating magnetic field (RMF) on the fading effect of Al–5Ti–1B in commercial pure Al. The results indicate that fading effect is obvious after adding Al–5Ti–1B to Al with a holding time of 20 min. It is fair to claim that the fading effect can be eliminated to a great extent when RMF with magnetic flux densities of 6 and 12 mT is applied until the temperature decreases to 662 °C, which is mainly attributed to the homogeneous distribution of TiB2 particles caused by forced convection. However, refinement performance of pure Al by Al–5Ti–1B can be greatly weakened by RMF with an increase in magnetic flux density to 18 mT, since strong convection aggravates the agglomeration of TiB2 particles. In addition, the inoculated Al treated by a RMF of 6 mT until solidification exhibits a coarser solidification structure compared to that treated until the temperature decreased to 662 °C, which is mainly due to the prolongation of solidification time caused by Joule heat under RMF as proved by thermal analysis. [ABSTRACT FROM PUBLISHER]

The intermediate frequency electromagnetic field and power ultrasonic field were applied during the direct chill (DC) casting process of Al-8 pct Si alloy. The effects of different physical fields on the solidification microstructure and mechanical properties were studied. The results show that compared to the conventional casting without any treatments, refined microstructures and improved mechanical properties can be obtained when the electromagnetic or ultrasonic field is applied individually. For the case of compound fields, the electromagnetic field can increase the ultrasonic treated region, while the ultrasonic field can enhance the refinement effect of electromagnetic field. Owing to the advantages of both electromagnetic and ultrasonic fields, the microstructure obtained under the compound fields is fine and uniform, leading to a remarkable enhancement of mechanical properties. The interaction mechanism between intermediate frequency electromagnetic field and power ultrasonic field was discussed. The present study may be useful for grain refinement and improvement of mechanical properties of alloys during the DC casting process which is now widely used in industry. [ABSTRACT FROM AUTHOR]

Many investigations have revealed that transition of melt structure can effectively influence the final solidification microstructures. In this study, ultrasonic treatment was applied to AI-20%Si melt and Sr-modified AI-20%Si melt at 720 °C (i.e. above liquidus of about 690°C) for 60 s, and then the melt was quickly quenched to room temperature. Experimental results show that ultrasonic treatment can refine the primary Si phase and cr-AI of AI-20%Si alloy; strontium can make the morphology of Si phase spheroidized and refined as Sr addition changes the faceted growth characteristic of Si phase; however, the refinement effect of ultrasonic treatment on the primary Si phase and a-AI is weakened by Sr addition. [ABSTRACT FROM AUTHOR]

The improved halide salt route has been employed to produce Al-3B master alloys with different microstructures. The micro-structural features of AlB particles exhibited different impacts on the grain refining response of Al-7Si alloy, evolving with the holding time after inoculation. Large blocky AlB particles suffer from an intense fading effect while strip-like particles are not effective enough at the 0.005 wt% B addition level. Among the various Al-3B master alloys, sample 1 containing fine, blocky AlB particles was revealed to be the most efficient in refining Al-7Si alloy. With inoculation of only 0.005%B of such alloy, the final grain size of Al-7Si alloy can reach 238 μm. Its grain refining efficiency was more or less retained for holding times up to 60 min. [ABSTRACT FROM AUTHOR]