Catalytic graphitization of PAN-based carbon fibers with electrodeposited Ni-Fe alloy

Ni-Fe alloy was electrodeposited on the surface of polyacrylonitrile （PAN）-based carbon fibers, and catalytic graphitization effect of the heat-treated carbon fibers was investigated by X-ray diffractometry and Raman spectra. It is found that Ni-Fe alloy exhibits significant catalytic effect on the graphitization of the carbon fibers at low temperatures. The degree of graphitization of the carbon fibers coated with Ni-Fe alloy （57.91% Fe, mass fraction） reaches 69.0% through heat treatment at 1 250 °C. However, the degree of graphitization of the carbon fibers without Ni-Fe alloy is only 30.1% after being heat-treated at 2 800 °C. The catalytic effect of Ni-Fe alloy on graphitization of carbon fibers is better than that of Ni or Fe at the same temperature, indicating that Ni and Fe elements have synergic catalytic function. Furthermore, Fe content in the Ni-Fe alloy also influences catalytic effect. The catalytic graphitization of Ni-Fe alloy follows the dissolution-precipitation mechanism.

Fabrication and characterization of electrodeposited nanocrystalline Ni-Fe alloys for NiFe_2O_4 spinel coatings

Nanocrystalline Ni-Fe FCC alloy coatings with Fe content of 1.3%-39%（mass fraction） were fabricated on the nickel substrates using a DC electrodeposition technique. The crystal structure, lattice strain, grain size and lattice constant of the Ni-Fe alloy coatings were studied by X-ray diffraction technique. The chemical composition and surface morphology of the FCC Ni-Fe alloy coatings were investigated with the energy dispersive X-ray spectroscopy（EDS） and atomic force microscopy（AFM）. The results show that the Fe content of the Ni-Fe alloy coatings has a great influence on the preferred orientation, grain size, lattice constant and lattice strain. FCC Ni-Fe alloy coatings exhibit preferred orientations of（200） or（200）（111）. With an increase of Fe content, the preferred growth orientation of（200） plane is weakened gradually, while the preferred growth orientation of（111） increases. An increase of the Fe content in the range of 1.3%-25%（mass fraction） results in a significant grain refinement of the coatings. Increasing the Fe content beyond 25% does not decrease the grain size of FCC Ni-Fe alloys further. The lattice strain increases with increasing the Fe content in the FCC Ni-Fe alloys. Since the alloys with Fe content not less than 25% has similar grain size（~11 nm）, the increase in the lattice strain with the increase of Fe content cannot be attributed to the change in the grain size.

EFFECT OF COMPOSITION ON HYDROGEN EMBRITTLEMENT IN Ni-Fe FCC ALLOYS

The ductility loss and threshold stress intensity,K_(IH)during hydrogen charging were measured for pure Ni and four Ni-Fe fcc alloys.The results show that ductility loss in 40Ni60Fe alloy and K_(IH)a 50Ni50Fe alloy have a minimum value.The variations of the amounts of hydride, hydrogen evolution and dislocation structure with composition have been investigated.The va- riation of hydrogen embrittlement susceptibility with composition measured by ductility loss and by K_(IH)or K_(IH)/K_C can be explained by means of the synthetical effects of amount of hydride,solutionized hydrogen and the extent of dislocation planarity on hydrogen embrittlement susceptibility.

Effects of minor B addition on microstructure and properties of AlCoFeNi eutectic high-entropy alloy

The simultaneous strengthening of mechanical and magnetic properties is an ideal fabrication strategy for soft-magnetic materials. A non-equiatomic Al19Co20Fe20Ni41 eutectic high-entropy alloy was prepared to investigate the alloying effect of B on the microstructure evolution, phase formation, mechanical and soft-magnetic properties. With the increase in B content, the microstructures of(Al19Co20Fe20Ni41)100-xBx alloys transformed from the initial lamellar eutectic structure(x=0) to the divorced eutectic structure(x>0.6). Fine borides precipitated in the intergranular phase(x≥0.6). The hardness of alloys increased from HV 328.66 to HV 436.34 and the compression mechanical performance displayed a transition from plastic material to brittle material. The Al19Co20Fe20Ni41 alloy possesses good soft-magnetic properties, and the minor B addition has little effect on it. Increasing the resistivity can effectively reduce the eddy current loss when used as a soft-magnetic material.

Microstructure and soft-magnetic properties of FeCoPCCu nanocrystalline alloys

Fe(83.2-x)CoxP(10)C6Cu(0.8)(x=0,4,6,8 and 10)alloys with a high amorphous-forming ability and good softmagnetic properties were successfully synthesized.Saturation magnetic flux density(Bs)is effectively enhanced from 1.53 T to 1.61 T for as-quenched alloy by minor Co addition,which is consistent well with the result of the linear relationship between average magnetic moment and magnetic valence.For Cocontained alloys,the value of corecivity(Hc)is mainly determined by magneto-crystalline anisotropy,while effective permeability(μe)is dominated by grain size and average saturation polarization.After proper heat treatment,the Fe(79.2)Co4P(10)C6Cu(0.8)nanocrystalline alloy exhibited excellent soft-magnetic properties including a high Bsof 1.8 T,a low Hcof 6.6 A/m and a highμeof 15,510,which is closely related to the high volume fraction of α-(Fe,Co)grains and refined uniform nanocrystalline microstructure.

Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials.A fabrication strategy to meet this requirement is therefore in high demand.Herein,bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700-1000℃,and their microstructures as well as mechanical and magnetic properties were investigated.The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al-and Ni-rich body-centered cubic(BCC)matrix and Fe-and Mn-rich face-centered cubic(FCC)precipitates both in the grain interior and along the grain boundaries.The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy.The FCC volume fraction could be increased by increasing the annealing temperature,thereby offering tunable properties.The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800℃.The alloy annealed at this temperature had an average BCC grain size of 12±3μm and FCC volume fraction of 41±4%.Correspondingly,the s aturation magnetization and coercivity reached 82.57 Am^2/kg and 433 A/m,respectively.The compressive yield strength and fracture strength were 1022 and 2539 MPa,respectively,and the plasticity was 33%.Owing to its adjustable microstructure and properties,the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.

Powder metallurgy synthesis of porous Ni-Fe alloy for oxygen evolution reaction and overall water splitting

Developing inexpensive and high efficient catalysts is essential for generating oxygen and hydrogen via water splitting.Herein,based on powder metallurgy,a Ni-Fe based compound(Ni8Fe2 alloy)with unique porous structure and controllable phase has been designed and synthesized.Without using a solvent or template,the alloy exhibits a porous structure with uniformly distributed multi-phase.The obtained Ni8Fe2 alloy exhibits an efficient oxygen evolution reaction(OER)performance and good longterm stability in alkaline electrolyte(i.e.1.0 M KOH).Additionally,an alkaline water splitting device has been assembled using porous Ni8Fe2 alloy as both anode and cathode materials.The system requires a cell voltage of 1.65 V to reach the 10 mA cm-2 current density for overall water splitting and maintains good stability for 25 h.The efficient electrocatalytic performance of the Ni8Fe2 alloy is owing to the unique porous microstructure,increased active sites and accelerated charge transfer.Consequently,the reaction kinetics of OER are significantly promoted.

Evolution of microstructure,mechanical and magnetic properties of electrodeposited 50% Ni-Fe alloy foil after thermal treatment

In order to expand the application of the electrodeposited Ni-Fe alloy foil,their mechanical and magnetic properties were studied after heat treatment.The development of grain growth during annealing was in-situ online investigated using a heating stage microscope,and the texture was analyzed via X-ray diffraction（XRD）and electron back-scattered diffraction（EBSD）.The results indicated that abnormal grain growth usually occurred during annealing at 1000-1050°C.The{111}oriented grains preferentially grew as the annealing temperature and holding time increased.The plasticities of the electrodeposited Ni-Fe alloy foils after heat treatment were better than those of the original samples.The excellent ductility was obtained without a loss in magnetic properties after annealing at 1100°C for 6h.

Bimetallic Ni-Fe catalysts derived from layered double hydroxides for CO methanation from syngas

Carbon deposition and sintering of active components such as nano particles are great challenges for Ni-based catalysts for CO methanation to generate synthetic natural gas from syngas. Facing the challenges, bimetallic catalysts with different Fe content derived from layered double hydroxide containing Ni, Fe, Mg, A1 elements were prepared by co-precipitation method. Nanoparticles of Ni-Fe alloy were supported on mixed oxides of aluminium and magnesium after calcination and reduction. The catalysts were characterized by Brunner- Emmett-Teller （BET）, X-ray diffraction, hydrogen tem- perature programmed reduction, inductively coupled plasma, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric techniques, and their catalytic activity for CO methanation was investigated. The results show that the Ni-Fe alloy catalysts exhibit better catalytic performance than mono- metallic catalysts except for the Ni4Fe-red catalyst. The Ni2Fe-red catalyst shows the highest CO conversion （100% at 260-350 ~C）, as well as the highest CH4 selectivity （over 95% at 280-350 ~C）, owing to the formation of Ni-Fe alloy. In stability test, the Ni2Fe-red catalyst exhibits great improvement in both anti-sintering and resistance to carbon formation compared with the Ni0Fe-red catalyst. The strong interaction between Ni and Fe element in alloy and surface distribution of Fe element not only inhibits the sintering ofnanoparticles but restrains the formation of Ni clusters.

Microstructural evolution and its influence on the impact toughness of GH984G alloy during long-term thermal exposure

The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984 G,used in 700℃ ultra-super critical coal-fired power plant,were investigated during thermal exposure at 650℃-750℃ for up to 10,000 h.The results show that the impact toughness at room tempe rature drops rapidly at the early stage during thermal exposure at 700℃ and then has no significant change even if after exposure for 10,000 h.The significant decline of the impact toughness is attributed to the coarsening of M_(23)C_(6) carbides at grain boundaries,which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement.The M_(23)C_(6) carbides have almost no change with further thermal exposure and the impact toughness also remains stable.Additionally,the impact toughness rises with the increase of thermal exposure temperature.The size of γ' after thermal exposure at 750℃ for10,000 h is much bigger than that at 650℃ and 700℃ for 10,000 h.There fore,the intragranular strength decreases significantly due to the transformation of the interaction between γ' and dislocation from stro ngly coupled dislocation shearing to Orowan bowing.More plastic deformation occurs within grains after thermal exposure at 750℃ for 10,000 h,which increases the impact toughness.

Heterostructured crystallization mechanism and its effect on enlarging the processing window of Fe-based nanocrystalline alloys

The harsh melt-spinning and annealing processes of high saturation magnetization nanocrystalline softmagnetic alloys are the biggest obstacles for their industrialization. Here, we proposed a novel strategy to enlarge the processing window by annealing the partially crystallized precursor ribbons via a heterostructured crystallization process. The heterostructured evolution of Fe_(84.75)Si_(2)B_(9)P_(3)_(C0.5)Cu_(0.75)(at.%)alloy ribbons with different spinning rate were studied in detail, to demonstrate the gradient nucleation and grain refinement mechanisms. The nanocrystalline alloys made with industrially acceptable spinning rate of 25-30 m/s and normal annealing process exhibit excellent magnetic properties and fine nanostructure. The small quenched-in crystals/clusters in the free surface of the low spinning rate ribbons will not grow to coarse grains, because of the competitive grain growth and shielding effect of metalloid elements rich interlayer with a high stability. Avoiding the precipitation of quenched-in coarse grains in precursor ribbons is thus a new criterion for the composition and process design, which is more convenient than the former one with respect to the homogenous crystallization mechanism, and enable us to produce high performance nanocrystalline soft-magnetic alloys. This strategy is also suitable for improving the compositional adjustability, impurity tolerance, and enlarging the window of melt temperature,which is an important reference for the future development of composition and process.

Upgrade of nickel and iron from low-grade nickel laterite by improving direct reduction-magnetic separation process

Low-grade saprolite nickel laterite,characterized by complicated minerals composition and fine-grained and complex dissemination,was commonly treated with a low recovery efficiency of Ni and Fe by conventional methods.Hence,an improved direct reduction and magnetic separation process was proposed.Meanwhile,the mechanisms on the enhanced growth of the Ni-Fe particles and the phase transformation in the nickel laterite pellets were explored.The low-nickel concentrates as a nucleating agent can obviously decrease the activation energy for growth of Ni-Fe alloy particles during the improved direct reduction process from 197.10 to 154.81 kJ/mol when the low-nickel concentrates were added from 0 to 20%.Hence,it is able to decrease nucleation barrier,induce the growth of Fe-Ni alloy particles and increase their average size.As a result,the size of Ni-Fe particles in the pellets from less than 10 lm grew to more than 20 lm,which is beneficial for the full liberation and recovery of Ni and Fe in subsequent magnetic separation process.Therefore,the preferable Ni-Fe alloy concentrates with 6.44%Ni and 82.48%Fe can be prepared with corresponding recovery rates of 96.90%and 95.92%,respectively,when adding 20%low-nickel concentrates.