BCC基Fe_(3.5)Cr_(1.5)NiAl_(0.8)多组元合金的显微组织稳定性与力学性能

研究温度对新型体心立方(BCC)基Fe_(3.5)Cr_(1.5)NiAl_(0.8)多组元合金(MCA)中有序椭圆状B2-NiAl纳米析出相的显微组织稳定性和力学性能的影响。采用XRD、EBSD、EPMA和TEM等检测方法对该多组元合金的显微组织和物相组成进行表征。结果表明,所设计的高含量椭圆状B2纳米析出相与BCC基体完全共格且能在1073 K高温下保持稳定,平均粒径为245.509~251.328 nm。铸态和热处理态(873 K≤T≤1073 K)合金具有独特的共格结构,这是由于低错配度的共格析出强化机制可使合金具有较高的屈服强度(809.2~1164.1 MPa)。随着热处理温度的进一步提高(1173 K≤T≤1273 K),B2纳米析出相的平均粒径逐渐粗化,载荷传递强化机制对其屈服强度提高起主要作用。

Effect of Ti content on microstructure and properties of TixZrVNb refractory high-entropy alloys

This study aimed to investigate the microstructure and mechanical properties of TixZrVNb(x=1,1.5,2)refractory high-entropy alloys at room and elevated temperatures.The TiZrVNb alloy consisted of the body-centered cubic(bcc)matrix with a small amount of V2Zr phase.The Ti1.5ZrVNb and Ti2ZrVNb alloys exhibited a single-phase bcc structure.At room temperature,the tensile ductility of the as-cast alloys increased from 3.5%to 12.3%with the increase in the Ti content.The TixZrVNb alloys exhibited high yield strength at 600°C,and the ultimate yield strength was more than 900 MPa.Softening occurred at 800°C,but the ultimate yield strength could still exceed 200 MPa.Moreover,the TixZrVNb alloys displayed low densities but high specific yield strengths(SYSs).The lowest density of TixZrVNb alloys was only 6.12 g/cm^3,but the SYS could reach about 180 MPa·cm^3·g^−1,which is better than those of most reported high-entropy alloys(HEAs).

Novel as-cast AlCrFe2Ni2Ti0.5 high-entropy alloy with excellent mechanical properties

We designed a novel Co-free AlCrFe2Ni2Ti0.5 high-entropy alloy(HEA)that features an excellent combination of strength and ductility in this study.The as-cast AlCrFe2Ni2Ti0.5 alloy showed equiaxed grains undergoing spinodal decomposition,which consisted of ultrafine-grained laminated body-centered cubic(bcc)phases and an ordered body-centered cubic(b2)phase,and some precipitates embedded in the b2 matrix.The bcc and b2 phases also feature a coherent interface.This unique structure impedes mobile dislocations and hinders the formation of cracks,thereby giving the AlCrFe2Ni2Ti0.5 HEA both high strength and plasticity.At room temperature,the as-cast AlCrFe2Ni2Ti0.5 alloy exhibited a compressive yield strength of 1714 MPa,an ultimate strength of 3307 MPa,and an elongation of 43%.These mechanical properties are superior to those of most reported HEAs.

Bibliometric analysis of subject trends and knowledge structures of gut microbiota

BACKGROUND Gut microbiota is an emerging field of research,with related research having breakthrough development in the past 15 years.Bibliometric analysis can be applied to analyze the evolutionary trends and emerging hotspots in this field.AIM To study the subject trends and knowledge structures of gut microbiota related research fields from 2004 to 2018.METHODS The literature data on gut microbiota were identified and downloaded from the PubMed database.Through biclustering analysis,strategic diagrams,and social network analysis diagrams,the main trend and knowledge structure of research fields concerning gut microbiota were analyzed to obtain and compare the research hotspots in each period.RESULTS According to the strategic coordinates and social relationship network map,Clostridium Infections/microbiology,Clostridium Infections/therapy,RNA,Ribosomal,16S/genetics,Microbiota/genetics,Microbiota/immunology,Dysbiosis/immunology,Infla-mmation/immunology,Fecal Microbiota Transplantation/methods,Fecal Microbiota Transplantation can be used as an emerging research hotspot in the past 5 years(2014-2018).CONCLUSION Some subjects were not yet fully studied according to the strategic coordinates;and the emerging hotspots in the social network map can be considered as directions of future research.

Effect of microstructure evolution on wear resistance of equal molar CoCrFeNi high-entropy alloy

Face-centered-cubic high-entropy alloys have excellent ductility and great potential for engineering applications.However,few studies have reported on the wear behavior under different loads.This study aimed to investigate the tribological behavior of CoCrFeNi highentropy alloy under different loads.The wear rate increased with the load,and the main wear behavior was abrasive wear.The cross-sectional microstructure of worn surface consisted of oxide,nanocrystalline,nanolaminated,and deformation layers.Under the higher loads,the deformation mechanism included dislocation slip and deformation twins,and shear bands also appeared.It was unexpectedly found that the wear rate increased sharply under high load,which was attributed to the formation of shear bands and microcracks in the nanocrystalline layer.The results successfully revealed the great influence of microstructure evolution on the wear rate,providing theoretical guidance for improving the wear resistance of face-centered-cubic high-entropy alloys in the future.

A Novel Series of Refractory High-Entropy Alloys Ti2ZrHf0.5VNbx with High Specific Yield Strength and Good Ductility

A series of Ti2ZrHf0.5VNbx( x = 0, 0.25, 0.5, 0.75 and 1.0) refractory high-entropy alloys were prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties.All the alloys displayed a simple BCC structure.The microstructures of the alloys changed from the initial single-phase columnar structure( x = 0) to dendrite microstructure( x > 0).At room temperature, all the alloys exhibited high ductility(with the compressive strains of more than 50%).With the increase in Nb content, the yield strength slightly decreased from 1160 to 980 MPa and the hardness dropped from 338 to 310 HV.Moreover, the alloys exhibited low density from 6.47 to 6.84 g/cm3 and high specific yield strength(SYS) from 143 to 179 kPa m3/kg.The comprehensive performance of ductility and SYS was superior to most of the reported highentropy alloys.The yield strength of the alloys increased from 405 to 859 MPa and from 85 to 195 MPa with the addition of Nb element at 873 K and 1073 K, respectively.

Antibacterial activities of a novel Cu-bearing high-entropy alloy against multi-drug-resistant Acinetobacter baumannii and Staphylococcus aureus

Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus(MRSA)are two prevalent pathogens and have developed high resistant to most antibiotics.Therefore,it is a pressing need to develop a new method to inhibit the spread of drug-resistant bacteria.Copper containing high-entropy alloy(HEA,Al0.4CoCr-CuFeNi)is a new kind of alloy material,which shows extensive antibacterial activity and mechanical properties in our previous research.This study further develops another HEA(CoCrCuFeNi)and evaluates its resistance against gram-negative A.baumannii and Gram-positive MRSA.The antibacterial tests show that the antibacterial rate of the HEA toward both bacteria reached nearly 99%,far better than the traditional copper-bearing 304 stainless steel(304 Cu-SS).The biofilm observation shows that the HEA could not only kill the planktonic bacteria,but also effectively inhibit the formation of biofilm.These data demonstrate that CoCrCuFeNi HEA possesses effective antibacterial and antibiofilm activities,making it a potential candidate for using in hospital,food industry,and domestic kitchens.

Novel(CoFe2NiV0.5Mo0.2)100-xNbx Eutectic High-Entropy Alloys with Excellent Combination of Mechanical and Corrosion Properties

The emergence of eutectic high-entropy alloys(EHEAs)offers new insights into the design of next generation structural alloys,which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures.In this work,a series of(CoFe2 NiV0.5Mo0.2)100-xNbx(0≤x≤12)EHEAs were designed and prepared via vacuum arc-melting.Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x=9.The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly.The volume fraction of the hard Laves phase is proportional to the Nb addition,leading to the strength increment yet at the expense of ductility at room temperature.In particular,the EHEA having4 at%Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%,while EHEAs containing 9 and10 at%Nb exhibit ultrahigh yield strengths of over 1.4 GPa.The effect of Nb addition on the corrosion resistance of this Crfree EHEA system was also studied.The EHEA containing 9 at%Nb has the best anti-corrosion performance in the 3.5 wt%NaCl solution at 298±1 K,indicating a good combination of mechanical and corrosion properties.

Tungsten-containing high-entropy alloys: a focused review of manufacturing routes, phase selection, mechanical properties, and irradiation resistance properties

Alloying is one of the most effective means to confer superior properties to metal materials.For far too long,conventional W-based alloys were generally improved by the addition of minor elements.The exploitation of conventional W-based alloy is restricted to the corner of multielement phase diagrams with tiny compositional space.High-entropy alloys(HEAs)are a novel kind of alloys consisting of multi-principal alloying elements(usually more than 4)and have attracted increasing attention,since they were first reported in 2004.The emergence of HEAs filled the gap of the unexplored central region of multielement phase diagrams.Among them,tungsten-containing HEAs(TCHEAs)exhibit excellent mechanical properties,especially at extraordinarily elevated temperatures.Moreover,recent studies showed that TCHEAs had outstanding irradiation resistance properties.TCHEAs might serve as a promising candidate for plasma-facing materials in the fusion reactor.Many characteristics of TCHEAs are different from other HEAs due to the addition of tungsten with ultrahigh-melting temperature.Here,this paper aimed to introduce the manufacturing routes of TCHEAs;review the phase selection,mechanical properties,and irradiation resistance properties of TCHEAs;and propose the future prospects of TCHEAs.

Constructing Bi_(2)WO_(6)-decorated TiO_(2) composite films for photocathodic protection of 304 stainless steel

Bi_(2)WO_(6) nanoplate/TiO_(2) nanowire and Bi_(2)WO_(6) nanoflower/TiO_(2) nanowire composite films were successfully prepared using a hydrothermal method.The results show that the light absorption for Bi_(2)WO_(6)/TiO_(2) composite films is extended to the visible region after Bi_(2)WO_(6) nanoplates and nanoflowers are assembled onto TiO_(2) nanowires.Furthermore,Bi_(2)WO_(6) nanoflower/TiO_(2) nano wire composite film exhibits a better absorption property compared to Bi_(2)WO_(6) nanoplate/TiO_(2) nanowire film,which is mainly ascribed to the narrower bandgap of Bi_(2)WO_(6) nanoflower compared to that of Bi_(2)WO_(6) nanoplate.The photocurrent density for Bi_(2)WO_(6) nanoflower/TiO_(2) nanowire and Bi_(2)WO_(6) nanoplate/TiO_(2) nanowire composite films can reach 95 and 62.5 μA cm-2,respectively,which are much higher than that obtained for a pure TiO_(2) nanowire film(25 μA cm-2).Meanwhile,under illumination,the pure TiO_(2) nanowire,Bi_(2)WO_(6) nanoplate/TiO_(2) nanowire and Bi_(2)WO_(6) nanoflower/TiO_(2) nanowire films can reduce the potential of the coupled 304 stainless steel in 3.5 wt.%NaCl solution by 299,719 and 739 mV,respectively.Thus,Bi_(2)WO_(6) nanoflower/TiO_(2) nanowire film is found to provide the best effective photocathodic protection for 304 stainless steel.This work not only provides an example of shape-dependent photocathodic protection based on Bi_(2)WO_(6) but also opens up new possibilities to design an ideal microstructure on the basis of semiconductor materials for future applications of photocathodic protection.

3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy

Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun AI-18Mn alloy （in wt%）. Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and a-A1 during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the a-A1 which propagates in a planar morphology.

Microstructural refinement and performance improvement of Cu-36 wt%Zn alloy by Al_(2)O_(3)nanoparticles coupling electromagnetic stirring

Cu-36 wt%Zn alloy is widely used in valves of water and heating and auto parts,etc.Nevertheless,the structure is still coarse,and performances are much poor.The structure and performances of Cu-36 wt%Zn alloy were investigated by adding Al_(2)O_(3)nanoparticles and stirring.Results indicate that by Al_(2)O_(3)nanoparticles coupling electromagnetic stirring,the Cu-36 wt%Zn alloy with refined microstructure was successfully prepared.The average grain size is refined by 99%compared with that without nanoparticles and stirring.The tensile strength(R_m)and percentage elongation after fracture(A11.3)increase by 20.58%and 19.40%,respectively,compared with that without nanoparticles and stirring.Nanoparticles increase heterogeneous nucleation rate by 50%compared with that without nanoparticles.The depth of dezincification layer decreases by 78.71%compared with that without nanoparticles and stirring,as protective layer(Cu-Al_(2)O_(3)-Zn)is completely formed around the grain boundaries.