Effect of Yttrium on Microstructure and Hot Corrosion Preformance of Laser Clad Co-Based Alloy

The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re-sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re-sistance to the salt mixture of 75% Na2SO4+25%NaCl at high temperature.The unique properties are ob-tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compactscale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusionof alloying elements.

Microstructure and wear resistance of Fe-based and Co-based coating of AISI H13

Fe-based and Co-based cladding layers were prepared on the surface of AISI H13 hot die steel by laser cladding technology.The microstructure,hardness and abrasion resistance of the two cladding layers were studied by means of optical microscope,scanning electron microscope,rockwell hardness tester,and high temperature friction and wear tester.Also,the red hardness of the cladding layers was measured,after holding the layers at 600℃ for 1 hour by muffle furnace and repeated 4 times.The rockwell hardness values of the substrate,the Fe-based and the Co-based alloy coating measured were HRC 47,HRC 52 and HRC 48,respectively.The red hardness values of the substrate and the Fe-based cladding layer were decreased,while that of the Co-based cladding layer was increased.The Co-based cladding layer has the minimal wear loss weight and friction coefficient among them.The wear mechanisms of the substrate,the Fe-based layer and the Cobased layer attribute mainly to abrasive wear,adhesion wear,and both of them,respectively.

Thermal Fatigue Behaviour of Co-Based Alloy Coating Obtained by Laser Surface Melt-Casting on High Temperature Alloy

A thermal fatigue behaviour of C o-based alloy coating obtained by laser surface melt-casting on the high tempe rature alloy GH33 was studied. The results show that after each time of thermal cycling, the final residual stress was formed in the melt-casting layer which i s attributed to the thermal stress and structural stress. Through the first 50 t imes of thermal cycling, the morphology of coating still inherits the laser cast ing one, but the dendrites get bigger; After the second 50 times of thermal cycl ing, corrosion pits emerge from coating, and mostly in the places where coating and substrate meet. The fatigue damage type of coating belongs to stress corrosi on.

High-Temperature Electric Properties and X-ray Photoemission Spectra of Layered Co-Based Oxides Bi_(2-x)La_xSr_2Co_2O_(8-δ)

Layered Co-based ceramics with a nominal composition Bi2-xLaxSr2Co2O8-δ (x=0.0, 0.4, 0.8, short by BLC-222) were prepared using conventional solid state reaction method. X-ray photoemission spectroscopy (XPS) was used to investigate their electronic structures. The cobalt ions are highly mixed valences of Co3+ and Co4+. The fraction of Co4+ almost keeps unchanged with the increase of x. The O-1s photoemission spectra show that there are lattice oxygen and chemical absorbed oxygen in all the samples. The substitution of Bi3+ by La3+ results in a change from metallic-like behavior to semiconductor behavior. This abnormal phenomenon means that La3+ plays a key role in effecting the electrical transport property of BLC-222. The O-Co covalence bond is strengthened by the increase of La3+, which results in the decrease of conductivity.

Preparation, Structures and Magnetic Properties of Two Co-based Clusters with Triangular Core and Cuboidal Core Geometries

Two novel Co-based clusters with the 2-(hydroxylmethyl)pyridine(hmpH)ligand,formulated as[Co3(hmp)6(hmpH)]×2NO3×3H2O(ZTU-3)and[Co4(hmp)4(CH3CO2)2(H2O)4]×2NO3(ZTU-4),have been successfully synthesized and structurally characterized.ZTU-3 features a triangular core geometry,while ZTU-4 exhibits a cuboidal core geometry.In addition,the magnetic properties of ZTU-3 and ZTU-4 are also all investigated.

Effect of Laser Annealing on Permeability Spectra in Co-based Amorphous Ribbon

We investigated the variation of permeability spectra and relaxation frequency in Co-based amorphous ribbon annealed by pulsed Nd:YAG laser at various annealing energy E_a. The complex permeability spectra varies sensitively with the annealing energy, where the spectra could be decomposed into two contributions from domain wall motion,μdw.(f) and rotational magnetization μrot(f) by analyzing the measured spectra as a function of driving ac field amplitude. The magnitude of μdw(f) and μrot(f) in dc limit shows maximum at E_a = 176 mJ. The maximum relaxation frequency for rotational magnetization, determined by μ"(f) curve, is about 700 kHz at Ea=62 mJ but that for wall motion is about 26 kHz at 230 mJ. These variations reflect the increase of magnetic softness and microstructural change by the annealing.

Recent progress in Co-based metal-organic framework derivatives for advanced batteries

To date,Co-based metal-organic frameworks(Co-MOFs)have drawn much attention owing to their advantages of easy preparation,high porosity and adjustable structure.Because of these enticing properties,numerous efforts have been devoted to their applications in energy storage and conversion.However,poor conductivity has become one of the biggest obstacles for large-scale use of pristine Co-MOFs.Subsequently,many attempts have been carried out to develop various Co-MOF derived materials as electrodes for rechargeable batteries in order to address the above-mentioned shortcoming and to enhance the electrical conductivity with improved stability during cycling.Moreover,in addition to improvement of Li-ion batteries in practical utilization,seeking for other rechargeable batteries is another urgent task due to the high cost and limited sources of metallic Li.Herein,by following the recent research progress,this review provides an overview of applications of Co-MOF derived materials in various rechargeable batteries including lithium-ion batteries,sodium-ion batteries,lithium-sulfur batteries,zinc air batteries and other rechargeable batteries,where they have been utilized as cathodes,anodes,separators and electrocatalysts.Accordingly,we categorize and compare the morphology driven electrochemical performance of various Co-MOF derivatives including porous carbon,cobalt oxides,cobalt chalcogenides,cobalt phosphides and corresponding composites.Finally,current challenges for large-scale production and commercialization of Co-MOF derived materials as well as some reasonable solutions have been discussed at the end.

Experimental investigation of a Portevin-Le Chatelier band in Ni–Co-based superalloys in relation toγ’precipitates at 500℃

The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlation(DIC).The DIC results showed that the serrated flow of the stress–strain curves was accompanied by localized deformation of the specimens.The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the lowγ’content alloy,and intergranular fracture with large fracture section in the highγ’content alloy.The Portevin–Le Chatelier(PLC)effect occurred in the investigated Ni–Co-based superalloys.Furthermore,the localized deformation of the highγ’content alloy was more severe than that of the lowγ’content alloy,and the band width was slightly larger.Moreover,for the first-time ever,a special propagation feature,namely±60?zigzag bands characterized by head-to-tail connections,was observed in the highγ’content alloy.

Effect of post-bond heat treatment on the microstructure and high temperature mechanical property of a TLP bonded γ'-strengthened co-based single crystal superalloy

Post-bond heat treatment(PBHT) applied to a transient liquid phase(TLP) bonding joint is an effective approach to remove the brittle borides and improve its properties.Herein,we proposed two types of PBHT strategies to obtain a TLP bonded γ'-strengthened Co-based single crystal superalloy,and the microstructural characteristics and tensile properties of the two heat treated joints were compared to identify the optimal PBHT strategy.The evolution of the brittle boride in the joint after the PBHT was studied by using in-situ microscopy.The experimental results allowed to provide a theoretic model to quantitatively evaluate the distribution of the brittle phase after the optimal PBHT and analyze the joint fractures to understand the failure mechanisms.The obtained results revealed that a post-bond solid solution treatment performed to the joint at a high temperature(over 1275℃) could decrease the area fraction of the boride from 7.2 % to 1.4 % and increase the elongation from 1.9 % to 7.8 %.This work emphasizes the relevance of solid solution temperature when a PBHT strategy is applied.

Selective Laser Melting of Carbon-Free Mar-M509 Co-Based Superalloy:Microstructure,Micro-Cracks,and Mechanical Anisotropy

In this work,the microstructural evolution,micro-crack formation,and mechanical anisotropy of the selective laser melted(SLM)carbon-free Mar-M509 Co-based superalloy were systematically studied under different linear energy densities(LED).Observation shows that the SLM Mar-M509 superalloy possesses a fully dense structure,whereas some microcracks exist along the building direction.The electron backscatter diffraction results reveal that dominant columnar grains tend to elongate along the building direction parallel to the XZ plane.Meanwhile,both a<001>near fiber texture and a{100}<001>near sheet texture are observed in different specimens.For the specimen with fiber texture,a high misorientation angle exists among different columnar grains,which aggravated the generation of micro-cracks under thermal stress.Higher LED results in higher micro-crack density in the SLM specimen due to higher thermal stress.Mar-M509 specimen fabricated under lower LED exhibits higher tensile strength due to more significant grain refinement.More prominent anisotropy of tensile performance was found in the high LED specimen,which can be attributed to the higher density of micro-cracks and crystallographic texture.Furthermore,the SLM Mar-M509 superalloy exhibits better mechanical properties than the traditional cast technique.In summary,this work can contribute to the development and the future application of SLM-fabricated Co-based superalloy.

Microstructure and Wear Resistance of Laser Cladded Co-based Superalloy Coating

Co-based superalloy coating was prepared on the stainless steel surface by laser cladding.The microstructure,phase constitutes and worn surface morphology of the coating were characterized by optical microscope,scanning electron microscope(SEM)with energy dispersive spectrum(EDS)and X-ray diffraction(XRD).The ambient temperature sliding friction and wear property of the coating was also tested.The experiments results showed that:the microstructures of the Co-based superalloy coating are"cellular crystal-coarse dendrite-tiny dendrite"in turn from bottom to surface,which consists ofγ-Co solid solution,Fe2Mo and Co7Mo6.The average micro-hardness of the laser cladding is 632 HV,which is 2 times higher than that of 304 stainless steel matrix.The ambient temperature sliding friction and wear property of the laser cladding is about 1～1.5 times in contrast to that of 304 stainless steel matrix.The better wear resistance of the coating is contributed to solution strengthening of Mo,as well as dispersion strengthening of Fe2Mo and Co7Mo6 hard phases.The failure mechanisms of the coating are pitting fatigue abrasion and grain-abrasion.

The highly dispersed Co-based nanoparticles encapsulated into porous N-doping carbon polyhedral with the low content of Ru modification as a promising cathode catalyst for long-life Li-O_(2)batteries

Lithium(Li)-O_(2)batteries have triggered worldwide interest due to their ultrahigh theoretical energy density.However,it is a long shot for the grand-scale applications of Li-O_(2)battery at current stage owing to its significant polarization,inferior cycling life,and irreversible decomposition of Li2O_(2).Herein,a facile way of preparing the highly dispersed Co-based nanoparticles encapsulated into porous N-doping carbon polyhedral with the low content of Ru modification(LRu@HDCo-NC)is explored through the pyrolysis of Co/Zn based zeolitic imidazole frameworks(ZIFs)containing Ru-based ligands.Even with the very small amount of Ru introduction(1.8%),LRu@HDCo-NC still exhibits the superior oxygen evolution reaction/oxygen reduction reaction(OER/ORR)performance and also inhibits side reactions in Li-O_(2)battery because of the abundant pores,plentiful surface N heteroatoms,and highly dispersed metal-based sites which are induced by the volatilization of Zn,and conductive/stable carbon skeleton derived from ZIFs.When applied in Li-O_(2)batteries,LRu@HDCo-NC cathode delivers a high discharge capacity of 15,973 mAh·g^(-1)at 200 mA·g^(-1),good capacity retention at higher rate(12,362 mAh·g^(-1)at 500 mA·g^(-1))and outstanding stability for>300 cycles with low voltage polarization of<2.3 V under a cut-off capacity of 1,000 mAh·g^(-1)at 500 mA·g^(-1).More critically,a series of ex situ and in situ characterization technologies disclose that the LRu@HDCo-NC cathodes can effectively promote the reversible reactions in Li-O_(2)batteries.

Formation of the anomalous microstructure in the weld metal of Co-based alloy/AISI 410 stainless steel dissimilar welded joint

The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding(EBW)technique.The anomalous microstructure containing the element transition zone(ETZ)and/or core of tail-like zone(CTLZ)is in the weld metal(WM)adjacent to the fusion line.The melting temperature difference between the WM and AISI 410 steel,melt stirring effect and element diffusion can trigger the formation of such anomalous microstructure.In particular,the larger distance of the region in WM away from the fusion line,the smaller CTLZ and larger ETZ occurred.Compared with the fine and ellipsoidal precipitates in the as-welded CTLZ,a large number of chain-type clustered precipitates were detected in the CTLZ and ETZ interface after the aging treatment at 566°C for 1000 h.The element diffusion under elevated temperature in WM is regarded as the crucial factor for such anomalous microstructure evolution during the aging treatment.

Carbide Behavior during High Temperature Creep in DZ40M Co-base Superalloy

The carbide behavior of a directionalIy solidified Co-base superalloy DZ40M has been investigatedafter creep at 700° and 900°. During the high temperature creep, a great amount of secondary carbide, M3C6 precipitated in alloy matrix. At 700℃, the M23C6 precipitation occurred in slip bands, indicating that it was stress-induced, while at 900℃, M23C6 formed surrounding the primary carbides, which is a characteristic of thermally aged alloy. The M23C6 particles pinned up dislocations and subgrain boundaries, strengthening the alloy matrix effectively. The creep crack initiation of DZ40M alloy was exclusively related to the primary carbides. The fracture of the primary carbide and the crack at the interface between them and matrix resulted in the crack formation. Furthermore, it was found that at 900℃, the surface of specimens was oxidized severely and the preferentially oxidized primary carbides acted as crack initiation sites.

EFFECT OF TRACE ELEMENT B ON MICROSTRUCTURE OF DIRECTIONALLY SOLIDIFIED Co-BASE SUPER ALLOY DZX40M

The effect of trace element B on microstructure of directionally slidified new type Co-base superalloy is studied systematically in this paper.It is found that the addition of B makes the incipient melting temperature of the alloy decline remarkably.Compared withthe alloy having a boron contenl of 0.05%,the incipient melting temperature of the alloywith 0.7% B decreases by 197℃.The primary and secondary dendrite arm spacings in-crease and the volume fraction of interdendritic carbides with fine microstructure becomesbigger with the enhancement of boron content.When the alloy is with 0.7wt%B,M3B2 precipitates in the interdendrites.

Effect of Rare-earth Element La on Co-base Superalloy

The effect of La element on the mechanicalproperties and constitution nearby grain boundaryin a Co-base superalloy Co-22Ni-22Cr-14k during760℃ ageing has been investigated by AES andmaterial testing. Results show that elementLa can be in a state of solid solution andsegregates mainly at the vicinity of grainboundaries. The prior segregation of La atomscan affect segregation behaviour of otherelements, so that exerts influence onmicrostructure of the alloy, Particularlyincreasing of La content can decrease Pconcentration at the vicinity of grain boundariesbut not decrease S concentration. S togetherwith La produce cosegregation effect. Thecontent of La has no obvious effect on hightemperature strength. When the content of Lacomes up to 0.02wt-％, it can obviously improvethe high temperature ductility.

Assessment of Co-Cr-Ni ternary system by CALPHAD technique

The Co-Cr-Ni ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ(Co,Ni),εCo and αCr phases were described by a substitutional solution model.The·phase was characterized by a three-sublattice model of (Co,Ni)8Cr4(Co,Cr,Ni)18 in order to reproduce its homogeneity range determined by experiments.A self-consistent set of thermodynamic parameters for each phase was derived.

Synthesis and High Temperature Thermoelectric Properties of Ca_(2.7-x)Er_(0.3)Na_xCo_4O_(9+δ)

Polycrystalline Ca2.7-xEr0.3NaxCo4O9+δ (x=0, 0.05, 0.1, 0.15) samples were prepared using a sol-gel process followed by hot-pressing technique sintering and their high-temperature thermoelectric properties were measured from 350 up to 1073 K. The results showed that with the increase of the dopant amount of Na, the electrical conductivity increased, while the Seebeck coefficient and thermal conductivity decreased. The electrical conductivity was dominated by polaron hopping conductivity mechanism above about 550 K and the Na+ substitution for Ca2+ could not change the transport mechanism. The dimensionless figure of merit ZT value reaches 0.31 for Ca2.55Er0.3Na0.15Co4O9+δ at 1073 K, which suggested that Ca2.7-xEr0.3NaxCo4O9+δ (x=0, 0.05, 0.1, 0.15) were good potential oxides for thermoelectric application.

Target-oriented confinement of Ru-Co nanoparticles inside N-doped carbon spheres via a benzoic acid guided process for high-efficient low-temperature ammonia synthesis

Ru-based heterogeneous catalysts have been used in a wide range of important reactions.However,due to the sintering of Ru nanoparticles their practical applications are somewhat restricted.Herein,for the first time we report a new and facile strategy to confine Ru and/or Co nanoparticles(NPs) in the channels of N-doped carbon using benzoic acid to guide the deposition location of Ru.The developed catalyst with confined RuCo alloy particles exhibits high resistance against Ru sintering and displays excellent activity and long term stability for NH3 synthesis,achieving an NH3 synthesis rate of up to 18.9 mmol NH_(3) gcat^(-1)h^(-1)at 400℃,which is ca.2.25 times that of the catalyst prepared without confinement(with metal deposited on the support surface).In the latter case,there is an increase of nanoparticle size from 2.52 to 4.25 nm together with ca.48% decrease of NH_(3) synthesis rate after 68 h at 400℃.This study provides a new avenue for simple fabrication of precious-metal-based catalysts that are highly resistant against sintering,specifically suitable for low-temperature synthesis of ammonia with outstanding efficiency.

Refractory Hard Alloys Elaborated by Casting of Ternary (Co, Ni Fe)-30Cr-2.5 to 5 wt% C Compositions

Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.