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 and 1Cr18Ni9Ti 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% Na_2SO_4+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 compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of 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 Co-based alloy coating obtained by laser surface meltcasting on the high temperature 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 is attributed to the thermal stress and structural stress.Through the first 50 times of thermal cycling,the morphology of coating still inherits the laser casting one,but the dendrites get bigger;After the second 50 times of thermal cycling,corrosion pits emerge from coating,and mostly in the places where coating and substrate meet.The fatigue damage type of coating belongs to stress corrosion.

Microstructures and properties of Co-based alloy coatings prepared on surface of H13 steel

The Co-based alloy coatings had been prepared by laser cladding and vacuum fusion sintering. Microstructures of the coatings were investigated and the performance of thermal cycling was also tested using scanning electron microscopy （ SEM） and X-ray diffraction （ XRD ）. The results show that the coatings and substrates combine well. The main phase compositions of laser cladding coating are T-Co, Cr23 C6 and Ni2 9 Cro. 7 Feo. 36, while vacuum fusion sintering coating consists of Co, Cr7 C3, and Ni2.9 Cro. 7 Feo. 36. After thermal cycling, the minimum hot cracking width of laser cladding coating is 14 μm; moreover, laser cladding coating maintains high hardness and hot-cracking susceptibility. Those are beneficial to high temperature wear resistance of hot work dies.

Oxidation of a Co-base Superalloy

The oxidation behavior of a cast polycrystalline Co-base superalloy was studied at temperatures from 900 to 1050℃ and analyzed by thermogravimetric analysis （TGA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicate that a cast Co-base superalloy follows the subparabolic oxidation kinetics at 900 and 1000℃, which are controlled by the growth of the inner Cr-rich layer, and that after oxidation at 1050℃ for 200 h, it almost exhibits the linear oxidation kinetics possible due to the volatility of Cr-rich oxide. A mixed scale forms on the alloy after prolonged oxidation. The oxide scale formed at 900 and 1000℃ is composed of an outer layer of spinel and an inner continuous Cr-rich layer and at I050℃ is composed of a very discontinuous Cr-rich layer.

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

The effect of La element on the mechanical properties and constitution nearby grain boundary in a Co-base superalloy Co-22Ni-22Cr-14k during 760℃ ageing has been investigated by AES and material testing. Results show that element La can be in a state of solid solution and segregates mainly at the vicinity of grain boundaries. The prior segregation of La atoms can affect segregation behaviour of other elements, so that exerts influence on microstructure of the alloy, Particularly increasing of La content can decrease P concentration at the vicinity of grain boundaries but not decrease S concentration. S together with La produce cosegregation effect. The content of La has no obvious effect on high temperature strength. When the content of La comes up to 0.02wt-％, it can obviously improve the high temperature ductility.

Influence of welding on low cycle fatigue properties of Co-based superalloy FSX-414

Co-based superalloys such as FSX-414 have been recently used in gas turbine first stage nozzles. During service, nozzles are exposed to low cycle fatigue, which can lead to cracking of these components. The cracks on these nozzles are usually welded with ttmgsten arc welding （TIG） using Co-based filler metals. In this paper, the effect of TIG on the tensile and low cycle fatigue properties of Co-based superalloy FSX-414 was studied at 950℃. The experimental results show that the yield and ultimate tensile stresses of welded and unwelded specimens are comparable to each other. But toughness of welded specimens is lower than that of unwelded ones. The low cycle fatigue properties of FSX-414 were studied at a strain rate of 3.3×10^-4 s^-1, strain ratio R=-1 （R=emin/emax） and Aet （total strain change） from 0.8% to 2%. In welded specimens, at high strain cycling, the nucleation and growth of cracks occur in the welded zone. But at Aet=0.8%, fracture occurs in the same zones of unwelded specimens. The results show that the total fatigue lives of the welded specimens are shorter than those of unwelded ones. In all of the low cycle fatigue tests, softening phenomena are observed.

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.

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 solidified 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 with the alloy having a boron content of 0.05 %, the incipient melting temperature of the alloy with 0.7 % B decreases by 197℃. The primary and secondary dendrite arm spacings increase and the volume fraction of interdendritic carbides with fine microstructure becomes bigger with the enhancement of boron content. When the alloy is with 0.7wt %B, M3B2 precipitates in the interdendrites.

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 Ea. 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 Ea = 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.

The manipulation of rectifying contact of Co and nitrogen-doped carbon hierarchical superstructures toward high-performance oxygen reduction reaction

Rational design and construction of oxygen reduction reaction(ORR)electrocatalysts with high activity,good stability,and low price are essential for the practical applications of renewable energy conversion devices,such as metal-air batteries.Electronic modification through constructing metal/semiconductor Schottky heterointerface represents a powerful strategy to enhance the electrochemical performance.Herein,we demonstrate a concept of Schottky electrocatalyst composed of uniform Co nanoparticles in situ anchored on the carbon nanotubes aligned on the carbon nanosheets(denoted as Co@N-CNTs/NSs hereafter)toward ORR.Both experimental findings and theoretical simulation testify that the rectifying contact could impel the voluntary electron flow from Co to N-CNTs/NSs and create an internal electric field,thereby boosting the electron transfer rate and improving the intrinsic activity.As a consequence,the Co@N-CNTs/NSs deliver outstanding ORR activity,impressive long-term durability,excellent methanol tolerance,and good performance as the air-cathode in the Zn-air batteries.The design concept of Schottky contact may provide the innovational inspirations for the synthesis of advanced catalysts in sustainable energy conversion fields.

Effect of Different Morphologies Induced by Solvent on ZIF-67 Derived Co@NC for Catalytic Phenol Hydrogenation

The Co@NC catalysts with different morphologies were prepared by two step process,solvent control growth and pyrolysis method.The polyhedral Co@NC-67P-450 catalyst has a relatively high CoNx content and exhibits excellent phenol hydrogenation activity(conversion 96.9%)at 160℃,3 MPa,which is higher than that of leaf shaped Co@NC-67L-450 catalyst(conversion 75.4%).We demonstrated Co_(3)O_(4)was reduced to the Co^(0)during the reaction.Moreover,CoNx species contribute to the superior hydrogenation activity of phenol.The Co-based catalysts can be easily recovered through the magnetic separation and performed the high stability.

Novel Soft Magnetic Co-Based Ternary Co-Er-B Bulk Metallic Glasses

In this work,a series of Co-based ternary Co-Er-B bulk metallic glasses(BMGs)with excellent soft magnetic properties and high strength were developed,and the local atomic structure of a typical Co_(71.5)Er_(3.5)B_(25) metallic glass was studied through in situ high-energy synchrotron X-ray diffraction and ab initio molecular dynamics simulations.The results reveal that the BMG samples can be obtained in a composition region of Co_(68.5-71.5)Er_(3.5-4)B_(25-27.5) by a conventional copper-mold casting method.The Co-Er-B metallic glasses possess stronger atomic bond strengths and denser local atomic packing structure composed of a higher fraction of icosahedral-like clusters but fewer deformed body-centered cubic and crystal-like polyhedrons,and they exhibit slower atomic diffusion behaviors during solidification,as compared to Co-Y-B counterparts.The enhancement in structural stability and the retardation of atomic-ordered diffusion lead to the better glass-forming ability of the Co-Er-B alloys.The smaller magnetic anisotropy energy in the Co-Er-B metallic glasses results in a lower coercivity of less than 1.3 A/m.The Co-Er-B BMGs exhibit high-yield strength of 3560-3969 MPa along with distinct plasticity of around 0.50%.

钴基耐磨硬质合金焊条电弧焊堆焊国产化试验研究

随着现代化煤化工业技术的蓬勃发展,对材料的耐磨损性能有了更高的要求,某些产品结构设计要求在母材表面堆焊钴基硬质合金,而进口堆焊焊条存在价格高、制造周期长等问题。为降低生产成本,需对钴基硬质合金堆焊焊条进行国产化试验研究。通过实验,掌握了国产钴基硬质合金堆焊焊条的焊接性,制定了合理的堆焊工艺,并通过堆焊层化学成分分析、剖面宏观检测以及表面硬度测定试验,在保证产品堆焊质量的前提下,满足堆焊层的性能要求。

Thermodynamic assessment of Co-Cr-W ternary system

The Co-Cr-W ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ-Co,ε-Co and α-Cr were described by a substitutional solution model.The σ,μ and R phases were described by three-sublattice models of（Co,W）8（Cr,W）4（Co,Cr,W）18,（Co,Cr,W）7W2（Co,Cr,W）4 and（Co,W）27（Cr,W）14（Co,Cr,W）12,respectively,in order to reproduce their homogeneity ranges.A self-consistent set of thermodynamic parameters for each phase was derived.The calculated isothermal sections at 1 000,1 200 and 1 350 ℃ are in good agreement with the experimental data.A eutectoid reaction of R μ＋γ-Co＋σ in this ternary system was predicted to occur at 1 022 ℃.

高压气井节流油嘴硬质合金和陶瓷的冲蚀对比实验

在高压气井试气和生产过程中,返排液或者生产流体会携带少量地层出砂,对节流油嘴产生非常严重的冲蚀。井下和地面节流油嘴通常选用耐冲蚀的陶瓷和硬质合金。通过自制的喷射式冲蚀装置,以压裂返排的0.3%的羟丙基瓜尔胶携砂液为介质,研究了冲击角度和流体流速对硬质合金和陶瓷两种材料冲蚀速率的影响规律。采用扫描电镜分析了冲击角度和流体流速对两种材料的微观形貌的影响。实验结果表明,硬质合金的抗冲蚀性能低于陶瓷,两者的冲蚀速率均随着冲击角度的增大而逐渐增大。在冲击角度为30°时,两者的冲蚀速率较为接近;在冲击角度为90°时,两者的冲蚀速率均达到最大值,并且,硬质合金的冲蚀速率约为陶瓷的2倍;两种材料的冲蚀速率随流速的增大而增加。当流速大于16 m/s时,冲蚀速率随流速增大而呈幂函数形式增长。扫描电镜结果表明,硬质合金和陶瓷均表现为明显的脆性冲蚀特征。与陶瓷相比,硬质合金的硬度较低而韧性较高,抗脆性断裂的能力较强,而抗微切削的能力较弱。硬质合金在低角冲蚀下以微切削为主要冲蚀机制,在高角冲蚀下以脆性断裂为主要冲蚀机制;陶瓷主要以脆性断裂为主要冲蚀机制。实验结果对高压气井节流油嘴选材以及寿命预测具有一定指导。

Phase equilibria in Co-rich region of Co-Ti-Ta system

The phase equilibria in Co-rich region of Co-Ti-Ta system were studied.The microstructure and XRD analysis together with EDS determination show that L12 type Co3Ti phase and Laves_C36_Co3Ta phase get equilibrium with α-Co phase from 1 000 to 1 200 ℃.The Co3Ti phase possesses a solubility of Ta higher than 10%,and the addition of Ta stabilizes the Co3Ti phase.The isothermal sections of the Co-Ti-Ta system in the Co-rich region at 1 000,1 100 and 1 200 ℃ were constructed according to the result.

钢结硬质合金材料实际应用的技术分析

本文根据钢结硬质合金材料的基本特点 ,对其实际应用于模具中进行了技术分析 ,采用该材料可大幅度提高模具使用寿命。

Effects of recrystallization on the low cycle fatigue behavior of directionally solidified superalloy DZ40M

The effects of recrystallization on low cycle fatigue behavior were investigated on directionally solidified Co-base superalloy DZ40M. Optical microscopy and SEM were used to examine the microstructure and fracture surface of the specimens. The mechanical testing results demonstrated that the low cycle fatigue property of DZ40M significantly decreased with the partial recrystallization. Fatigue cracks initiate near the carbides and the grain boundaries with slip-bands. Both the fatigue crack initiation and propagation can be accelerated with the occurrences of recrystallized grain boundaries.