Role of micro-Ca/In alloying in tailoring the microstructural characteristics and discharge performance of dilute Mg-Bi-Sn-based alloys as anodes for Mg-air batteries

The influence of micro-Ca/In alloying on the microstructural charac teristics,electrochemical behaviors and discharge properties of extruded dilute Mg-0.5Bi-0.5Sn-based(wt.%)alloys as anodes for Mg-air batteries are evaluated.The grain size and texture intensity of the Mg-Bi-Sn-based alloys are significantly decreased after the Ca/In alloying,particularly for the In-containing alloy.Note that,in addition to nanoscale Mg_(3)Bi_(2)phase,a new microscale Mg_(2)Bi_(2)Ca phase forms in the Ca-containing alloy.The electrochemical test results demonstrate that Ca/In micro-alloying can enhance the electrochemical activity.Using In to alloy the Mg-Bi-Sn-based alloy is effective in restricting the cathodic hydrogen evolution(CHE)kinetics,leading to a low self-corrosion rate,while severe CHE occurred after Ca alloying.The micro-alloying of Ca/In to Mg-Bi-Sn-based alloy strongly deteriorates the compactness of discharge products film and mitigates the"chunk effect"(CE),hence the cell voltage,anodic efficiency as well as discharge capacity are greatly improved.The In-containing alloy exhibits outstanding discharge performance under the combined effect of the modified microstructure and discharge products,thus making it a potential anode material for primary Mg-air battery.

Properties of Ti-Based Hydrogen Storage Alloy

An efficient and safe hydrogen storage method is one of the important links for the large-scale development of hydrogen in the future. Because of its low price and simple design, Ti-based hydrogen storage alloys are considered to be suitable for practical applications. In this paper, we review the latest research on Ti-based hydrogen storage alloys. Firstly, the machine learning and density functional theory are introduced to provide theoretical guidance for the optimization of Ti-based hydrogen storage alloys. Then, in order to improve the hydrogen storage performance, we briefly introduce the research of AB type and AB2 type Ti-based alloys, focusing on doping elements and adaptive after treatment. Finally, suggestions for the future research and development of Ti-based hydrogen storage alloys are proposed. .

Novel cobalt base superalloy and its high-temperature flow behavior

A novel cobalt base superalloy containing titanium and aluminum was investigated through metallography, tensile test, and high-temperature isothermal compression deformation. The results show that proper content of titanium and aluminum with can improve the strength and ductility of the cobalt base superalloy. The Co3（Ti,Al） compound with L12 structure precipitates when the novel superalloy is aged at 800℃ for 20 h. The e phase with hcp structure also precipitates when the superalloy is deformed by 28% and then aged at 650℃ for 4 h. The e phase can exist at 800℃. The superalloy has excellent high-temperature mechanical properties. Its maximum flow stress at 850℃ is in the range of 360-475 MPa when the strain rate is between 0.0021 and 2.1 s^-1. The flow stress of the superalloy during high-temperature deformation can be described by the Zener-Hollomon parameter with a hot deformation activation energy of 397 kJ.mol^-1.

Microstructure and Fractural Morphology of Cobalt-based Alloy Laser Cladding

The solidification features,micro segregation,and fracture characteristics of cobalt based alloy on the substrate of 20CrMo steel by laser cladding were studied by using electron microscopy.Experimental results show that the fine columnar grains and cellular dendrite grains are obtained which are perpendicular to the coating/substrate interface;the primary arms are straight while the side branches are degenerated;the microstructure consists of primary face centered cubic (fcc) Co dendrites and a network of Cr enriched eutectic M23C6 (M=Cr,W,Fe) carbides;the micro segregation is severe for the rapid heating and cooling of laser cladding;the typical brittle intergranular fracture occurs in cobalt based laser cladding layer.

Effects of Y_2O_3 on the microstructure and wear resistance of cobalt-based alloy coatings deposited by plasma transferred arc process

Cobalt-based alloys with different Y2O3 contents were deposited on Q235A-carbon steel using plasma transferred arc （PTA） welding machine. The effect of Y2O3 on the microstructure and wear resistance properties of the cobait-based alloys were investigated using an optical microscope, a scanning electron microscope （SEM）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that a cobalt-based solid solution with a face-centered cubic crystal structure was presented accompanied by the secondary phase M7C3 with a hexagonal crystal structure in the Y2O3-free cobalt-based alloy coating. Several stacking faults exist in the cobalt-based solid solution. The addition of Y2O3 leads to the existence of the Y2O3 phase in the Y2O3-modified coatings. Though stacking fault exists in the Y2O3-modified coatings, its density increases. The addition of Y2O3 can refine the microstructure and can increase the wear resistance properties when its contents are less than or equal to 0.8 wt.%. However, further increase of its contents will lead to the agglomeration of undissolved Y2O3 particles at the γ-Co grain boundary, and will lead to a coarse microstructure and lower wear resistance properties.

MECHANISM OF SECONDARY M_(23)C_6 PRECIPITATION AROUND MC IN A COBALT-BASE SUPERALLOY

Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of the MC. Two mechanisms were suggested,i.e. the in situ reaction, MC+γ→M23C6+C, and the direct reaction, M+C→M23C6,in which MC acted as a carbon source.

Cobalt phthalocyanine-based conjugated polymer as efficient and exclusive electrocatalyst for CO_(2) reduction to ethanol

Electrocatalytic conversion of carbon dioxide to high value-added chemicals is a promising method for solving the energy crisis and global warming.Electrochemical active metal-containing conjugated polymers have been widely studied for heterogeneous carbon dioxide reduction.In the present contribution,we designed and synthesized a stable cobalt phthalocyanine-based conjugated polymer,named CoPPc-TFPPy-CP,and also explored its electro-catalytic application in carbon dioxide reduction to liquid products in an aqueous solution.In the catalyst,cobalt phthalocyanine acts as building blocks connected with 1,3,6,8-tetrakis(4-formyl phenyl)pyrenes via imine-linkages,leading to mesoporous formation polymers with the pore size centered at 4.1nm.And the central co-balt atoms shifted to a higher oxidation state after condensation.With these chemical and structural natures,the catalyst displayed a remarkable electrocatalytic CO_(2) reduction performance with an ethanol Faradaic efficiency of 43.25%at-1.0V vs RHE.While at the same time,the electrochemical reduction process catalyzed by cobalt phthalocyanine produced only carbon monoxide and hydrogen.To the best of our knowledge,CoPPc-TFPPy-CP is the first example among organic polymers and metal-organic frameworks that produces ethanol from CO_(2) with a remarkable selectivity.

EFFECT OF REVERT RECYCLE TIMES ON MICROSTRUCTURE AND FATIGUE PROPERTIES IN COBALT-BASE SUPERALLOY K640S

Effect of revert cycles on microstructure and fatigue properties of cast cobalt base superalloy K640S has been investigated. The results show that: at 70 times of cool heat cycles, there were microcracks found in seven times revert and ten times revert. With the increasing of thermal fatigue cycles, the crack of revert grows a little faster than virgin. When the cycle time reaches 200, the crack length for both virgin and reverts have been as long as 2mm. The low cycle fatigue life has no remarkable change, with the increase of revert cycles at 815℃, 360MPa ,0 5Hz. With the times of cycles increasing, it is found that the content of impurity and gas in alloy change a little, and there is no obvious change for dendrite microstructure.

Influences of the microstructure on the wear resistance of cobalt-based alloy coatings obtained by plasma transferred arc process

The microstructure, substructure, and wear characteristic of cobalt-basedalloy coatings obtained by plasma transferred arc (PTA) process were investigated using opticalmetallurgical microscope, X-ray diffraction (XRD), scanning electron microscope (SEM), transmissionelectron microscope (TEM), and dry sand abrasion tester (DSAT). The aging effect on the structureand wear resistance of the cobalt-based PTA coating was also studied. The results show that theas-welded coating consists of cobalt-based solid solution with face-centered cubic structure andhexagonal (Cr,Fe)_7C_3. There are a lot of stacking faults existing in the cobalt-based solidsolution. After aging at 600 deg C for 60 h, the microstructure becomes coarse, and another carbide(Cr,Fe)_(23)C_6 precipitates. As a result, the wear mass loss of the aged sample is higher than thatof the as-welded sample.

Valence electron structures dependences of structural stability and properties of REX_(3)(RE=rare earth;X=In,Tl)and RE(In,Co)3 alloys

Intermetallic compounds REIn3(RE=rare earth)have attracted much attention due to their unique characteristics:crystal field effect,Kondo effect,superconductivity,heavy fermion,and antiferromagnetism,and their cobalt diluted alloys exhibit the ferromagnetic half-metallic characteristics at room temperature.In this study,an empirical electron theory(EET)is employed to investigate systemically the valence electronic structure,the thermal and magnetic properties of REX_(3) and their cobalt diluted alloys for revealing the mechanism of physical properties.The calculated bond length,melting point,and magnetic moment match the experimental ones very well.The study reveals that structural stability and physical properties of REX_(3) and their cobalt dilute alloys are strongly related to their valence electron structures.It is suggested that the structural stability and cohesive energy depend upon the covalent electron,the melting point is modulated by covalent electron pair,and the magnetic moment is originated from 3d magnetic electron.The ferromagnetic characteristics of Co-diluted REIn3 alloys is originated from the introduction of strong ferromagnetic Co atom,but,a competition is caused between the electron transition from valence electron to magnetic electron on d orbit and its reversal electron transformation with increasing the content of cobalt,which results in the formations of diluted magnetic Gd(In,Co)3 alloy with minor amount of cobalt and strong magnetic Nd(In,Co)3 alloy with doping more Co atoms.

Understanding the creep behaviors and mechanisms of Mg-Gd-Zn alloys via machine learning

Mg-Gd-Zn based alloys have better creep resistance than other Mg alloys and attract more attention at elevated temperatures.However,the multiple alloying elements and various heat treatment conditions,combined with complex microstructural evolution during creep tests,bring great challenges in understanding and predicting creep behaviors.In this study,we proposed to predict the creep properties and reveal the creep mechanisms of Mg-Gd-Zn based alloys by machine learning.On the one hand,the minimum creep rates were effectively predicted by using a support vector regression model.The complex and nonmonotonic effects of test temperature,test stress,alloying elements,and heat treatment conditions on the creep properties were revealed.On the other hand,the creep stress exponents and creep activation energies were calculated by machine learning to analyze the variation of creep mechanisms,based on which the constitutive equations of Mg-Gd-Zn based alloys were obtained.This study introduces an efficient method to comprehend creep behaviors through machine learning,offering valuable insights for the future design and selection of Mg alloys.

Fatigue crack propagation behavior of K40S cobalt-base superalloy at elevated temperature

Fatigue crack propagation behavior of K40S cobalt-base superalloy under ambient atmosphere at 700 ℃ and 900 ℃ was investigated. The detailed fatigue crack propagation and fracture mechanism under the alternating loads were studied. The results show that, there is a defined threshold for K40S alloy at elevated temperatures. The fatigue threshold is 23.9 MPa·m 1/2 at 700 ℃ and 12 MPa·m 1/2 at 900 ℃. The significant decrease of the threshold with increasing temperature is associated with the oxidation induced embrittlement at crack tip. Observation on the fatigue fracture surfaces indicates a ductile fracture mechanism related to the fatigue crack growth.

Microstructure of Nano-Y_2O_3/Cobalt Based Alloy Composite Coating by Laser Cladding

Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.

Microstructure of cast γ-TiAl based alloy solidified from β phase region

The microstructures and phase transformation of Ti-43Al-4Nb alloy in as-cast and heat-treated states were investigated by using optical microscopy, scanning and transmission electron microscopy as well as differential scanning calorimetry. The results show that a fine microstructure of the as-cast alloy can be obtained by solidifying through the β phase. γ grains can nucleate directly from the β phase. The coexistence of β phase and γ phase along primary α grain boundaries contributes to the decrease in the grain size of the as-cast alloy. The phase transformation sequence during solidification of the Ti-43Al-4Nb alloy is suggested as L→L＋β→β→α＋β→α＋βr→α＋γ＋βr→lamellae（α2＋γ）＋γ＋βr. The microstructure of the alloy after heat treatment at 1 250 ℃ for 16 h exhibits a certain coarsening compared with that of the as-cast state. The remnant β phase can be removed by the heat treatment process due to the diffusion of Nb and the non-equilibrium state of β phase.

Hot corrosion behavior of Ni-xCr-6.8Al based alloys

The hot corrosion behaviors of as-cast and preoxidized Ni-xCr-6.8Al based alloys in the mixture of Na2SO4＋25% NaCl at 873 K were studied. The results show that the mass loss of Ni-xCr-6.8Al based alloys decreases with the increase of Cr content. Preoxidation improves the resistance to corrosion regardless of the concentration of Cr. The kinetics of as-cast Ni-12Cr-6.8Al and Ni-16Cr-6.8Al based alloys fits the parabolic law well, while that of the as-cast Ni-20Cr-6.8Al based alloy fits the power law. The kinetics of all the preoxidized samples obey the logarithmic law. The mechanism of the as-cast alloys can be well explained by the acid-base melting model. The behavior of the preoxidized alloys is found to be mainly determined by the properties of the oxide layer formed during the preoxidation to a large extend.

Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

Friction and wear behaviors of Nb-Ti-Si-Cr based ultrahigh temperature alloy and its Zr-Y jointly modified silicide coatings

Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.

Hot corrosion behavior of Ni–16Cr–xAl based alloys in mixture of Na_2SO_4-NaCl at 600 ℃

The hot corrosion behaviors of Ni–16Cr–xAl（x=4.5%, 6.8%, 9.0%, mass fraction） based alloys in Na2SO4–25% NaCl molten salts at 600 °C were investigated. The effects of pre-oxidation and Al content on the resistance to hot corrosion were examined. The hot corrosion resistance of Ni–16Cr–xAl based alloy with Al addition from 4.5% to 9.0% increases with increasing Al content. The alloy with Al content of 9.0% shows the highest hot corrosion resistance among the examined alloys because more β–NiAl phases are obtained to sustain the Al2O3 scale repaired during hot corrosion. Pre-oxidized specimens have a superior hot corrosion resistance compared with the as-cast specimens, due to a protective oxide scale formed after pre-treatment.

Microstructure and microhardness of directionally solidified and heat-treated Nb-Ti-Si based ultrahigh temperature alloy

Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.