- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
In recent years, the sudden rise of high entropy alloys (HEAs) has become a hot research topic in the field of metal materials. The high entropy alloy is located in the central region of phase diagram, which has broad alloy composition space and possible formation of microstructure. The synergistic regulation of composition and preparation process can obtain richer structure. Unconventional chemical structure is expected to break through the performance limit of traditional anti-wear and lubricating alloys. In this work, the classification of wear-resistant HEAs was discussed. The effects of the addition of chemically active metals, soft metals and refractory metals on the wear resistance and lubrication properties of HEAs were analyzed. The effects of non-metallic elements and ceramic phases on the tribological properties of HEAs matrix composites were summarized. The effects of heat treatment and surface engineering technology on the surface microstructure and tribological behavior of HEAs were reviewed. The design method of HEAs with anti-wear lubrication under severe working conditions was discussed. The future research and application of HEAs in the field of friction and wear were prospected. High entropy alloys have great potential to solve the bottleneck problems of traditional alloys, such as to realize stable lubrication and anti-wear under extreme working conditions and to ensure anti-wear under specific functions.
The friction and wear of mechanical parts mainly occurs on the surface of the material, and about 80% of the failures of parts are caused by surface wear.Friction and wear increase the loss of material and energy, and reduce the reliability and safety.Using laser cladding technology to prepare a high entropy alloy coating on the surface of the substrate can achieve a good metallurgical combination between the coating and the substrate, so as to achieve the purpose of improving surface wear resistance.The main factors affecting the wear resistance of the high entropy alloy coating are the mechanical and physical properties of the coating material (such as hardness, plasticity and toughness), defects generated during the cladding process (such as surface roughness, pores and cracks), friction conditions (such as high temperature environment and corrosive environment).In this paper, the influencing factors and strengthening mechanism of laser cladding high entropy alloy coatings were reviewed and summarized.First of all, the influence of laser process parameters (such as laser power, laser scanning speed, spot diameter) and post-treatment processes (such as heat treatment and rolling) on the quality and performance of the coating were explained.Secondly, the influence of component element selection, high temperature environment and corrosive environment on the wear resistance of the coating was described.Finally, the problems existing in the preparation of high entropy alloy coatings by laser cladding technology were analyzed, and the future development trends were forecasted, such as developing new materials based on far-equilibrium material design theory, using electric field-magnetic field synergy or laser-ultrasonic vibration composite technology to improve the wear resistance of coatings, etc.
The meaning and characteristics of refractory high entropy alloys were briefly described, and the preparation methods of various refractory high entropy alloys (bulk, film and coating) were summarized.The comprehensive properties of refractory high entropy alloys were emphatically expounded. It was suggested that the composition design should be optimized by constructing a special database of refractory high entropy alloys, and the manufacturability of different preparation methods should be focused on. In view of the shortcomings of high room temperature brittleness, high density and high cost of refractory high entropy alloys at present, different preparation methods could be selected according to the properties of refractory high entropy alloys for future industrial application.
The equiatomic CoCrFeNiMn high entropy alloys (HEAs) has been successfully manufactured using direct laser deposition (DLD) technique. The size and number of porosities, the microstructures along the height of samples and the tensile properties of DLDed HEAs prepared under room (293 K) and cryogenic temperatures (77 K and 200 K) were investigated. The results show that DLDed HEAs exhibit directional solidification, forming dendritic columnar grains with long pores at the grain boundary in bottom regions and transiting to equiaxed grains close to top regions. And in the top regions, the pores are round and the numbers are greatly reduced. Compared with tensile properties of DLDed HEAs, the 77 K tensile samples cut from the top region have better performance, but the elongation of 293 K tensile samples in the middle region and 200 K tensile samples in the bottom region are similar, owing to the difference of porosity and microstructure in the two regions.
High entropy alloys (HEAs) show better wear resistance and corrosion resistance than traditional alloys, which has gradually become a research hotspot in the field of metal materials. CoCrFeNiMnAlWx (x=0.12, 0.15, 0.19)high entropy alloys with different W content were prepared by metal thermal reduction. The effects of W addition on phase structure, microstructure and performance of CoCrFeNiMnAlWx high entropy alloy were investigated. The phase structure, microstructure and element distribution of the alloy were characterized by XRD, SEM and EDS. Surface performance tester and electrochemical workstation were adopted to detect corrosion resistance and wear resistance performance of CoCrFeNiMnAlWx high entropy alloy. Results show that the high entropy alloys with different W contents are both composed of BCC phases with two different lattice contents. There is no obvious change in the micro-tissue of the dendrites with the increase content of W. However, microstructure between dendrites changes significantly with the change of W content. The wear resistance and corrosion resistance have certain degree of improvement, the friction coefficient and wear rate of CoCrFeNiMnAlW0.19 alloy are 0.684 and 1.06×10-5 mm3/(N·m) respectively. The wear mechanism is converted from adhesive wear to the combination of adhesion wear and abrasive particle wear, and finally is transformed to friction wear. The wear resistance performance of CoCrFeNiMnAlWx high entropy alloy in 3.5% NaCl solution is increased with the increase of W content. Corrosion current density is decreased from 6.08×10-6 A/cm2 to 1.72×10-6 A/cm2, and the corrosion rate is gradually reduced.
Macroscopic and microscopic mechanical responses, damage behavior and microstructure evolution of NiCoCrFe high entropy alloys (HEAs) during finite deformation under quasi-static loading were investigated by experiments and crystal plasticity finite element method. The microstructure of NiCoCrFe before and after tensile deformation was characterized by electron backscattering diffraction technique(EBSD). The internal state variables of dislocation density and continuum damage factors were introduced into the CPFEM model by modifying the strengthening model and the flow criterion, and the NiCoCrFe related model parameters were determined by combining the stress-strain curves of the tensile test. The results show that the CPFEM model considering the dislocation density and damage can effectively describe the macroscopic and microscopic mechanical responses of NiCoCrFe. CPFEM model can reasonably predict the deformation shape and size of NiCoCrFe necking region, among which, the length of the necking region obtained in the experiment is 7% smaller than the predicted result, and the width of the necking region predicted by CPFEM is 23% larger than the experimental result. The texture evolution predicted by CPFEM model after NiCoCrFe tensile deformation is in good agreement with the results that characterized by EBSD, showing weak (100)//RD and strong (111)//RD fiber texture. In the analysis of the 3D micro- structure damage, the damage predicted by the current CPFEM model appears as an inter-granular damage mechanism at the grain boundary where stress and dislocation density are concentrated, and the damage gradually expands to the grain interior with the increase of deformation.
Soft magnetic materials have been widely applied in modern industries as energy materials. In recent years, with the increasingly high frequency and miniaturization of magnetic components, as well as the call of energy conservation and environmental protection, the development and research of high-performance soft magnetic material are of great important significance. The present work generalized the development history of soft magnetic alloys comprehensively, from the viewpoints of chemical compositions, microstructures, magnetic properties, application fields, and advantages and disadvantages of different soft magnetic alloys. The involved alloy systems include primarily traditional crystalline alloys, amorphous/nanocrystalline alloys, and high entropy alloys. It is found that the microstructure induced by alloy compositions plays a dominant role in soft magnetic property, especially the coercivity. Then the influence factors on the coercivity of alloys and the related micro-mechanisms were discussed, in which the grain size in traditional alloys or particle size in nano-crystalline alloys is crucial to achieve lower coercivity. Therefore, the development of the micro-mechanisms of coercivity in high entropy soft magnetic alloys was described. Finally, it was expected that high entropy soft magnetic alloys would be more beneficial to modulate alloy properties due to the diversification of microstructures induced by the mixing of multi-principal elements, which shows great potential to serve as a new generation of high temperature soft magnet materials.
Nowadays, metal-based catalysts have become the mainly catalyst in the field of catalysis, which also have some problems such as difficult to be separated and recycled, easily remain, high cost, as well as instability of catalysts and substrate. One effective way to solve the above problems is loading with polymer carrier.Cellulose is the most abundant green and natural polymer on the earth. As a catalyst carrier, cellulose has the excellent characteristics with wide source, biodegradability, non-toxic and good biocompatibility. Meanwhile, cellulose also has a large number of hydroxyl groups on the molecular structure, which can be easily modified and loaded with metal catalysts in various ways. In this paper, the advance of cellulose supported zero valent metal nanoparticles and non-zero valent metal as catalysts were reviewed, and the catalytic activities of the supported catalysts in redox reaction, Heck reaction, Suzuki reaction and other reactions were summarized; by comparing the mechanism of action between carrier and metal in the system, the synergy between different loading modes and the difference of catalytic activity were expounded.
In order to achieve the applications of the ZnO nanorod arrays in the novel nanostructured solar cells, it is necessary to tailor and control the nanorods' morphological, optical and electrical properties. The ZnO nanorods arrays were fabricated by electrodeposition. The physical properties such as the diameter, density, distance, optical band gap energy, near band emission and Stokes shift can be adjusted by the use of In(NO3)3 and NH4NO3.The characterizations such as scanning electron microscopy, X-ray diffraction spectrometer and photoluminescence were used to measure the samples' morphology, crystal property, transmission and reflection and photoluminescence properties. According to the measurement results, the ZnO nanorod arrays' density is reduced to 5.9×109 cm-2 and the distance between nanorods is enlarged to 108 nm by using NH4NO3. The nanorods' diameter is decreased to 22 nm. The use of In(NO3)3 leads to the blue shift of the ZnO nanorods' optical band gap energy by 100 meV. The optical band gap energy is further tailored between 3.41 eV and 3.55 eV by using NH4NO3. The ZnO nanorods' Stokes shift can be decreased to 19 meV by using NH4NO3, resulting in the effective suppression of the non-radiative recombination.
A water-soluble perylene bisimide derivative, N, N'-di(2-succinic acid)-perylene-3, 4, 9, 10-tetracarboxylic bisimide (PASP) was synthesized by using 3, 4, 9, 10-perylenetetracarboxylic dianhydride and L-aspartic acid as starting materials. The PASP were grafted onto graphitic carbon nitride (g-C3N4) via hydrothermal method to prepare PASP modified g-C3N4 hybrid photocatalyst (g-C3N4-PASP). The composition, structure, morphology and optical properties of the prepared g-C3N4-PASP samples were typically characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM), transmission electron microscopy(TEM), UV-Vis diffuse reflectance spectroscopy(UV-Vis DRS), and solid-state fluorescence spectroscopy. In addition, the photocatalytic activities of the prepared g-C3N4-PASP photocatalysts were evaluated by decomposition of methylene blue(MB) pollutant in water solution under visible light. The results reveal that PASP can be facilely linked to the g-C3N4 covalently via amide bond by hydrothermal treatment; compared to pristine g-C3N4, the g-C3N4-PASP possesses obviously higher specific surface area, dramatic red shifted absorption edge of 614 nm, and more efficient charge separation. Therefore, the visible light photo-catalytic degradation of MB pollution in water over the g-C3N4-PASP is notably improved. The g-C3N4-PASP could degrade 99.4% of MB dyes in 60 min under visible light irradiations (λ >420 nm), with a pseudo-first-order rate constant 2 times higher than that of pristine g-C3N4.
Four kinds of fluorinated carbon cathodes were fabricated with the industrial carbon materials (activated carbon, spherical graphite, expanded graphite and industrial graphene) to realize the universal applications of lithium/fluorinated carbon primary battery. The morphology, crystalline structure, chemical structure and electrochemical performance were systematically studied by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Raman spectra (Raman), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectro scopy(XPS), N2 adsorption-desorption isotherms and electrochemical test, etc. It was found that the fluorinated industrial graphene shows the highest specific capacity (945.4 mAh·g-1) at the discharge current density of 20 mA·g-1, which may benefit from the monofluorocarbon structure, high specific area and stable carbon structure. The fluorinated active carbon has the highest initial discharge voltage due to the abundant semi-covalent C—F bond, but its discharge voltage declines rapidly caused by the unstable structure. Although the fluorinated spherical graphite and fluorinated expanded graphite have the similar structure with the fluorinated industrial graphene, their specific capacities are lower, due to the presence of the highly fluorinated carbon atoms (CF2 and CF3). However, at high discharge current density, the fluorinated spherical graphite and fluorinated expanded graphite possess the similar value with the fluorinated industrial graphene. Considering the cost, they may be more suitable for the high power applications.
The Al-Ti-C alloy was extruded in multiple passes in a continuous manner by continuous equal channel angular pressing process. Through observation of the microstructure evolution, the mechanism of grain refinement and changes in mechanical properties were discussed.The results show that continuous equal channel angular pressing process can effectively refine the microstructure of Al-Ti-C alloy, and the grain size is reduced to about 1 μm.The deformation induction is the most important grain refinement mechanism in the deformation process.The accumulation of high density dislocations causes cracks at the interface between the Al matrix and TiAl3 and voids inside the TiAl3. The cracks further propagate through the entire TiAl3 particles, ultimately leading to the refinement of the second phase TiAl3 structure.At the same time, the pinning mechanism and shearing mechanism of the fine second phase TiAl3 structure promote the refinement of the Al matrix.After one pass of continuous equal channel angular pressing, the hardness of the alloy increases most obviously, which is 59.2% higher than that of the original state.With the increase of the number of extrusion passes, the increasing trend of hardness slows down, the plasticity of the alloy decreases, and toughness increases.
Selective laser melting(SLM) 4Cr5MoSiV1 steel has good strength/hardness and wear resistance, which is the important guarantee to improve its service life. In order to optimize the structure and properties of 4Cr5MoSiV1 steel formed by selective laser melting, the microstructure, microhardness, tensile properties and wear resistance of 4Cr5MoSiV1 steel samples were studied under the different forming angles. The results show that with the increase of forming angle, the heat accumulation between the melt channels of sample is decreased, the grain size is decreased, and the fine grain strengthening is enhanced, so the microhardness of the sample is increased. With the increase of forming angle, the number of slip lap surfaces and the degree of slip of tensile sample are increased, and the normal stress at the melt boundary is decreased, so the tensile strength and elongation after fracture of the sample are increased. The wear mechanisms of the wear sample are mainly adhesive wear and oxidation wear, and the wear resistance of the sample is increased with the increase of forming angle. At the same forming angle, after repeated heat accumulation on the surface of the sample bottom layer, the fine grain strengthening and solid solution strengthening are weakened, and the microhardness and wear resistance are reduced, so the microhardness and wear resistance of the sample are decreased. The microhardness, wear resistance and tensile properties of 4Cr5MoSiV1 steel sample formed by SLM are positively correlated. The mechanical properties of sample are the highest at 45° forming angle, the highest tensile strength is 1576.5 MPa, the highest elongation is 17%, the highest micro-hardness of upper surface is 608.4HV, and the lowest wear resistance of the upper surface is 4.95×10-9 kg·N-1·m-1.
The hot deformation behavior of Al-8.9Zn-1.3Mg-0.1Sc-0.1Er-0.1Zr aluminum alloy was studied by Gleeble-3800 thermal simulator. The hot processing map of the alloy in the temperature range of 380-440 ℃ and strain rate range of 0.01-10 s-1 was established.The phase in the alloy was analyzed by XRD, SAED and EDS. The microstructure after hot deformation was observed by OM and TEM. The optimum range of hot working parameters is as follows: 400 ℃ < T < 440 ℃, 0.01 s-1 <
In order to study the thermal deformation behavior of Zirlo alloy at ranges of 550-700 ℃ deformation temperature and 0.01-10 s-1 strain rate, the Zirlo alloy was subjected to compression under condition of isothermal and constant strain rate by using the Gleeble-3800 thermal simulated test machine. Through introducing strains on the basis of the Arrhenius type hyperbolic sine function equation, an Arrhenius constitutive model was developed based on strain compensation, and founded on a combination of dislocation density evolution causing work hardening model and phenomenological softening model, a segmented phenomenological constitutive model was constructed. The results show that the flow stress of Zirlo zirconium alloy increases with the decrease of temperature and the increase of strain rate, the flow stress exhibits higher temperature sensitivity at low strain rate, and flow stress curves separately exhibit characteristics as work hardening, dynamic recovery and dynamic recrystallization under different deformation conditions. Through error analysis, it was revealed that errors of the most stresses predicted by the Arrhenius constitutive model based on strain compensation are within 15%, which exhibits high accuracy. The maximum relative average absolute errors of the segmented phenomenological constitutive model are less than 3%, exhibiting an accuracy of over 97%. The segmented phenomenological constitutive model can accurately predict the stress-strain curve of the Zirlo alloy and has good expansibility; moreover, it can preliminarily predict the type of the stress-strain curve and has good practicability.
The effects of melt temperature on the residual stress of thermoplastic polyurethane(TPU)sheets during the injection molding process were studied by birefringence. The results indicate that the residual stress in the near gate area is higher than that in the far gate area and decreases with the increase of the melt temperature. The residual stress of cross section in the two directions is characterized. The injection molded TPU sheets have obvious skin-core structure and zero stress layer. The thickness of core layer increases with the melt temperature rising. The results of residual stress analysis show that the residual stress of core layer is dominated by the flow residual stress, while it is the result of superposition of flow and thermal residual stress in the surface layer. Besides, the warpage deformation is directly related to the distribution of residual stress. The change of the dimensions of the TPU sheets is directly caused by the release of flow residual stress.
AZ31/7075 composite with the addition of Zn foil (about 100 μm in thickness) in the dissimilar material interface was successfully fabricated by pre-extrusion+caliber rolling composite process. The microstructure evolution especially for the composite interface was characterized by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) and the microhardness test was also performed. The effect of the Zn intermediate layer on the product during the extrusion and caliber rolling was explored. The results show the hard 7075 Al alloy as the core can refine the grain size of AZ31 alloy. In addition, introducing Zn intermediate layer can reduce or completely avoid the formation of Mg-Al intermetallic compounds. The temperature increased by extrusion and deformation results in the remelting of eutectic Mg-Zn phase, and the diffusion of both elements from the solid to the liquid phase are accelerated. However, discontinuous cracks can be observed in the Mg-Zn diffusion layer but will be healed after caliber rolling. The MgZn2 intermetallic compound generated at Mg-Zn diffusion layer has high hardness (161HV), but the overall hardness of bonding layer is not changed a lot due to thinner thickness of the Mg-Zn diffusion layer after deformation.
Laminating method is one of the key factors affecting the thermal shock resistance of SiCf/SiC composites prepared by prepreg paving process. Based on the cohesion model, 1200 ℃ high temperature water quenching tests and finite element simulation studies were carried out on SiCf/SiC composite square samples with different orthogonal lay-up methods, which were prepared by the precursor immersion pyrolysis(PIP) process. The results show that the surface temperature of the sample drops sharply during the water quenching process, and there is a large temperature difference between the core and the surface. The temperature difference between the corner and the core can reach up to 1077 ℃. The main failure modes are interlaminar delamination and matrix cracking, and the delamination position is related to the layering method. Moreover, significant differences in the delamination displacement can be observed, due to the difference in the orthogonal lay-up mode: tacking displacement of the main interlaminar delamination of [0/90] and [0/90/0] can reach 0.61 mm, while the [0/0/90/90] layer cracking displacement is only 0.04 mm. In addition, the cracking displacement of the main interlaminar delamination increases gradually with the increase of water quenching time, while the secondary cracks will undergo crack closure after opening.
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