Investigation on the formation mechanism of ordered carbide (FeMn)<Subscript>3</Subscript>AlC in the Al added twinning-induced plasticity steels

The spinodal composition zone in Al added Fe-Mn-Al-C twinning-induced plasticity（TWIP） steels can be determined by contents of Al and C and aging temperature together, based on the thermodynamic analysis. Precipitation of ordered（FeMn）₃AlC carbide by the mechanism of spinodal decomposition occurs in the C-rich and Al-rich zone with low aging temperature. Increase of aging temperature shrinks spinodal composition zone to the high Al and C contents. As a result, the precipitation of（FeMn）₃AlC carbide alters from spinodal decomposition to classical nucleation-growth manner gradually. Further calculation indicates that the diffusion of Al can play a key role in determining the growth rate of（FeMn）₃AlC carbide at high aging temperature.     

Investigation on the Formation Mechanism of Ordered Carbide (FeMn)_3AlC in the Al Added Twinning-Induced Plasticity Steels

The spinodal composition zone in Al added Fe-Mn-Al-C twinning-induced plasticity(TWIP) steels can be determined by contents of Al and C and aging temperature together, based on the thermodynamic analysis. Precipitation of ordered(FeMn)_3AlC carbide by the mechanism of spinodal decomposition occurs in the C-rich and Al-rich zone with low aging temperature. Increase of aging temperature shrinks spinodal composition zone to the high Al and C contents. As a result, the precipitation of(FeMn)_3AlC carbide alters from spinodal decomposition to classical nucleation-growth manner gradually. Further calculation indicates that the diffusion of Al can play a key role in determining the growth rate of(FeMn)_3AlC carbide at high aging temperature.     

Microstructure evolution during remelting of high solid fraction ZL101 alloy

This work deals with the reheating process for semi-solid thixoforming of ZL101 (AlSi7Mg) alloy. The semi-solid state can decrease the viscosity and the resistance while sheared because of the evolutional behavior, which is characterized by a solid-like behavior at rest and a liquid flow during shearing. The microstructure evolution of ZL101 alloy at different temperatures from 540 to 580 °C has been studied. Results show that the eutectic temperature can affect the transformation speed of semi-solid structure. Semi-solid microstructures with high solid fraction can be obtained by controlling the reheating time in less than 20min, while at the temperature lower than the eutectic temperature it needs more than one hour. Another character of semi-solid ZL101 alloy is the segregation of microstructures in semi-solid state, in which the liquid phase between the solid phases can flow freely and lead to the shrinkage of the sample during the heating process. As the holding time goes on, more shrinkage holes appear and change the surface of the specimen. These shrinkage holes are replenished by the liquid phase during compression deformation, resulting in the segregation of the components.     

Purification effects of C2Cl6 on A00 aluminum

The effects of several fluxes on purification, microstructures and properties of A00 aluminum have been studied. The experimental results and analyses indicate that many cracks and large porosities exist in the surface film above the melt purified by C₂Cl₆ and that the film is floc and mostly composed of Al₂O₃ and pure aluminum, which carries many carbon particles and AlCl₃ not fully volatilized. And then over 50% (mass fraction) of the all-melting residue is pure aluminum, which is one of the major reasons for high melting loss. Moreover, because of a mass of gas bubbles and a state of seethe, there are many inclusions which size is under 10 ??m in the microstructure of A00 aluminum purified with C₂Cl₆ or fluxes containing C₂Cl₆. With this purifying method, the aluminum crystal grains are extended along the radius that was observed firstly and the average crystal size of A00 aluminum are about 100?C150 ??m. In addition, small size inclusions have little affected on tensile strength and micro inclusions under 10 ??m have little affected on elongation.     

Phase transitions relating to the pozzolanic activity of electrolytic manganese residue during calcination

Electrolytic manganese residue（EMR） is generated from electrolytic manganese metal（EMM） industry, and its disposal is currently a serious problem in China.The EMR were calcined in the interval 100—900℃to enhance their pozzolanic activity and characterized by the differential thermal analysis-thermogravimetry（TGDTA）, X-ray diffraction（XRD）,infra-red（IR） and chemical analysis techniques with the aim to correlate phase transitions and structural features with the pozzolanic activity of calcined EMR.Prom the phase analysis and compressive strength results,it is found that the EMR calcined within 700—800℃had the best pozzolanic activity due to the decomposition of poorly-crystallized CaSO₄ under the reducing ambient created by the decomposition of（NH₄）₂SO₄.The appearance of reactive CaO mainly contributes to the good pozzolanic activity of EMR calcined within 700—800℃.The crystallinity of Mn₃CO₄ increases leading an unfavourable effect on the pozzolanic behaviour of EMR calcined at 900℃.The developed pozzolanic material containing 30%（mass fraction） EMR possesses compressive strength properties at a level similar to 42.5^# normal Portland cement,in the range of 41.5—50.5 MPa.Besides,leaching results show that EMR blend cement pastes have excellent effect on the solidification of heavy metals.     

Catalytic Combustion of Lean Methane Assisted by Electric Field over Pd/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Catalysts at Low Temperature

A series of Pd/Co₃O₄ catalysts were prepared by Self-Propagating High-Temperature Synthesis (SHS) method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co₃O₄ catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co₃O₄ catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (H₂-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS), the mechanism of catalytic oxidation of CH₄ over Pd/Co₃O₄ catalysts in electric field was proposed. The catalytic combustion of CH₄ occurs only when the temperature is higher than 250 °C normally, but when electric field was applied, the whole process of CH₄ oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co₃O₄ to release the lattice oxygen, resulting in the increase of PdO_x and the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH₄. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.     

Super-capacitive performances of nickel foam supported CeO2 nanoparticles

This paper designs and fabricates CeO₂ nanoparticles on a large scale by hydrolysis and oxidation of cerium carbide. The electrochemical supercapacitor behavior of CeO₂ nanoparticles was investigated. The nickel foam (NF) supported CeO₂ nanoparticles show a high areal capacitance of 119 mF/cm², demonstrating a strong synergistic effect between NF and CeO₂ nanoparticles. The high capacitance of the CeO₂/NF nanoparticles is possibly due to an improved conductivity by NF and a better utilization of CeO₂ nanoparticles.     

Explore the possibility of forming fcc high entropy alloys in equal-atomic systems CoFeMnNiM and CoFeMnNiSmM

The multi-principal high-entropy alloys (HEAs) are promising new alloys. However, it is a challenge to screen out the suitable composition from the diverse combinations. Referring to the prototype AuCu₃ with AB₃-L1₂ structure, where it becomes a face-centered cubic (fcc) structure if element A and B are the same element, the site occupying tendencies of the elements and thermodynamic functions are predicted by using the sublattice model supported with first-principles total energy calculations. By considering the Gibbs energy of formation and the configurational entropy, the fcc HEAs in available literatures are examined, and the results of the quinary system with equal-atomic composition CoFeMnNiM and the hexbasic system with equal-atomic composition CoFeMnNiSmM are reported, respectively, where the element M is selected from the rest of the periodical table. When M=Cr, Zn, Ru, Rh, Pd, Re, Os, Ir, or Pt in the quinary systems CoFeMnNiM and when M=Ru, Pd, or Pt in the hexbasic systems CoFeMnNiSmM, respectively, the alloys are recommended to be potential fcc HEAs. The new approach opens a new way to mine the rich ores of HEAs.     

添加稀土元素对硬质合金物理机械性能和切削性能的影响

本文研究了稀土元素的添加种类和添加量对ＹＴ１５硬质合金物理机械性能和切削性能的影响。研究结果表明，添加稀土元素后硬质合金刀片的抗弯强度以及刀具耐用度等显著提高；添加Ｓｍ，Ｙ，ＳｍＰｒ效果较好，并且添加量存在一量佳范围，本文还对添加稀土元素后硬质合金的改机理作了探讨。     

2．25Cr─1Mo钢焊接接头蠕变断裂时碳化物状态的研究

选择２２５Ｃｒ─１Ｍｏ钢手工电弧多层焊焊接头进行了不同工艺规范的持久强度试验，用透射电镜对蠕变断裂时母材和焊缝碳化物的形态、大小和分布进行了分析，采用选区电子衍射和ＥＤＡＸ能谱分析方法对析出的碳化物类型进行了鉴定．结果表明，试验中出现的碳化物类型分别为Ｆｅ３Ｃ，Ｍｏ２Ｃ和Ｍ２３Ｃ６．在试验时间较长应力较小时，断裂试样中针状Ｍｏ２Ｃ在晶内聚集粗化，块状Ｍ２３Ｃ６在晶界聚集粗化，这种碳化物分布状态是影响蠕变断裂的主要因素．     

Friction and wear performances of hot filament chemical vapor deposition multilayer diamond films coated on silicon carbide under water lubrication

Tribological properties of chemical vapor deposition (CVD) diamond films greatly affect its application in the mechanical field. In this paper, a novel multilayer structure is proposed, with which multilayer diamond films are deposited on silicon carbide by hot filament CVD (HFCVD) method. The different micrometric diamond grains are produced by adjusting deposition parameters. The as-deposited multilayer diamond films are characterized by scanning electron microscope (SEM) and white-light interferometry. The friction tests performed on a reciprocating ball-on-plate tribometer suggest that silicon carbide presents the friction coefficient of 0.400 for dry sliding against silicon nitride (Si₃N₄) ceramic counterface. With the water lubrication, the corresponding friction coefficients of silicon carbide and as-deposited multilayer diamond films further reduce to 0.193 and 0.051, respectively. The worn surfaces indicate that multilayer diamond films exhibit considerably high wear resistance.     

Photothermal effect for Fe3O4 nanoparticles contained in micelles induced by near-infrared light

Near infrared (NIR) light induced photothermal effect for Fe₃O₄ nanoparticles, contained in Pluronic F127 micelles, has been studied and it exhibits high photothermal converting efficiency. Heat is found to be rapidly generated in micelles containing Fe₃O₄ nanoparticles by NIR laser irradiation. Upon irradiation at 808 nm light and with mass concentration of Fe₃O₄ nanoparticles in 4 g/L, the micelle temperature increase is higher than 34°C for 10min irradiation. The maximum temperature of micelles containing Fe₃O₄ nanoparticles in 4 g/L reaches 62°C.     

Microstructure of hot-dip galvanized Zn-Al-Mg alloy coating

The microstructure of hot-dip galvanized Zn-11%Al-3%Mg-0.2%Si alloy coating was studied in this article. X-ray diffraction analysis revealed the coating is composed by Zn, Al and MgZn₂ phase. Optical microscope (OM) and scanning electron microscope (SEM) observations showed the coating is occupied by snowflake-like dendrite, double hexagonal organization and eutectic. The coating backbone was the dendrite considered to be a phase of hexagonal close-packed (HCP) structure judging form its morphology according to the crystal growth way in the coating. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) researches on the dendrite suggested that an intermediate Zn-Al phase was formed at high temperature, then decomposed into a type of Zn-Al granular eutectoid after cooling down to room temperature, while the eutectoid Zn and Al had a certain crystallographic relationship. The coating solidification process and the grain crystal structure were discussed.     

Microstructure and hardness of Ni-xSi alloys

The microstructure and hardness of conventionally solidified Ni-xSi (x = 21.4%, 22%, 24%, 26%) alloys were investigated. The solidification microstructures of different Ni-Si alloys were observed by optical microscope (OM) and scanning electron microscope (SEM) and the phase composition was indentified under the help of energy dispersive X-ray (EDX) analysis. The macro- and micro-hardness of the Ni-Si alloys at room temperature were also examined. The experimental results indicated that both the microstructure and hardness closely depended on the Si content. Due to the vast formation of primary ??-Ni₃₁Si₁₂ phase, the hardness of Ni-26.0%Si alloy was significantly improved compared with that of Ni-21.4%Si eutectic alloy. However, the fracture toughness was greatly weakened simultaneously. The (?? ₁-Ni₃Si+??-Ni₃₁Si₁₂) lamellar eutectoid structure formed in the primary ??-Ni₃₁Si₁₂ phase exhibited better ductility than single ??-Ni₃₁Si₁₂ phase at the cost of relatively small hardness reduction.     

Influence of soaking temperature on microstructure of multi-pass compression deformation for low carbon steels

The influence of soaking temperature on microstructure of high temperature multi-pass compression deformation for two low carbon steels (steel A: w _C = 0.032% and w _Mn = 0.25%; steel B: w _C = 0.165% and w _Mn = 0.38%) is studied on the thermal-mechanical simulator in order to rationalize the hot-rolling schedule of low-carbon steel and to promote the low-temperature heating technology. The results show that the microstructures of steel A are almost not affected by reducing soaking temperature, but the acicular ferrite forms in steel B when the soaking temperature is reduced from 1 200 to 1 170°C, due to its smaller initial austenite grain size according to recrystallization kinetics theory.     

片状马氏体的平行生长

用光镜、透射电镜对8种 Fe—C,Fe-Cr-C 及 Fe-Ni-C 合金中的片状马氏体进行了一般观察、原位观察及动态观察.结果发现,在这些合金中片状马氏体不但呈大角度分布,而且也能平行分布.片状马氏体的平行生长主要表现为两种形态.一种是并生一对片状马氏体紧靠在一起同时形核,同时长大;另一种是附生几个片状马氏体连续形核、连续长大.本文认为,片状马氏体平行生长的原因,在于马氏体转变的塑性协调作用.     

Measurement of swarm parameters of c-C4F8/CO2 and its insulation characteristics analysis

In c-C₄F₈ and c-C₄F₈/CO₂ mixtures, the swarm parameters including ionization coefficient, attachment coefficient and effective ionization coefficient were obtained at the ratio of the electric field strength to the gas density between 150–550 Td by the steady-state Townsend (SST) method. Static breakdown voltages at each ratio were also measured at the SST condition. The limiting field strengths were obtained by two methods: computing the density-normalized effective ionization coefficient as a function of the overall density-reduced electric field strength; and measuring static breakdown voltages as a function of the product of gas density and electrode separation. Good agreement was obtained by these two methods, which ensures the correctness of the former method. The limiting field strengths of c-C₄F₈ and c-C₄F₈/CO₂ mixtures were compared with those of pure SF₆, SF₆/CO₂ mixtures and pure c-C₄F₈. It is found that buffer gas CO₂ does not reduce the limiting field strengths of c-C₄F₈ greatly, the limiting field strengths of c-C₄F₈/CO₂ mixtures are higher than those of SF₆/CO₂ mixtures or even pure SF₆, and so c-C₄F₈/CO₂ mixtures are suggested to be possible substitutes for SF₆. Foundation item: the National Natural Science Foundation of China (No. 50777041)     

Effect of Cu Co-doping on the magnetism of Zn0.95Co0.05O films

Zn_0.95?x Co_0.05Cu _x O (atomic ratio, x = 0?C8%) thin films are fabricated on Si(111) substrate by reactive magnetron sputtering method. Detailed characterizations indicate that the doped Cu ions substitute the Zn²⁺ ions in ZnO lattice. The doped Cu ions are in +1 and +2 mixture valent state. The ferromagnetism of the Zn_0.95?x Co_0.05Cu _x O film increases gradually with the increase of the Cu⁺ ion concentration till x = 6%, but decreases for higher Cu concentration. Experimental results indicate that the increase of ferromagnetism is not owing to the magnetic contribution of Cu⁺ ions themselves, but owing to the enhancement of magnetic interaction between Co²⁺ ions, which suggests that p-type doping of Cu⁺ ions plays an important role in mediating the ferromagnetic coupling between Co ions.     

Dry milling of the ultra-high-strength steel 30CrMnSiNi2A with coated carbide inserts

The ultra-high-strength steel (UHSS) plays an important role in the mechanical industry because of their special performances. The machinability of 30CrMnSiNi2A steel was studied in dry milling with two different coated tools in the present work. This paper introduced that 30CrMnSiNi2A steel was a kind of difficult-to-machine materials. The results showed that the cutting force components of feed direction and cutting width direction, i.e. F x and F y , increased slightly with increasing the cutting speed and feed rate. The values of axial force component F z were much larger than F x and F y , and increased obviously with increasing the milling speed. The workpiece surface had the minimum roughness at the cutting speed of 150 m/min. The physical vapor deposition (PVD) coated ((Ti, Al)N-TiN) insert was more suitable for machining 30CrMnSiNi2A steel than the chemical vapor deposition (CVD) coated (Ti(C, N)-Al 2 O 3 ) insert. Moreover, the main failure modes of PVD-coated insert were micro-chipping and coating spalling. The wear modes of CVD-coated insert were ploughing, coating spalling, and cratering. The serious adhesive wear and the abrasion with some adhesion were the main wear mechanism of PVD- and CVD-coated inserts, respectively.     

Grain refining mechanism of carbon inoculation on Mg-Al alloy

The processing parameters and refining mechanism of Mg-Al alloy treated with a newly developed carbon inoculant under different conditions were investigated experimentally in this work. Results show that the finest ??-Mg grain in AZ91D alloy can be obtained after processing at about 740°C, and the average grain size of ??-Mg grain decreases from about 180.4 to 85.6 ??m by adding mass fraction w _in = 1% inoculant into melt. However, no evident refinement was achieved with excessive inoculant for Mn-free Mg-9Al alloy. Scanning electron microscope (SEM) photo, energy dispersive spectroscopy (EDS) analysis on the Mn-contained intermediate phase and differential scanning calorimetry (DSC) results indicate that Mn element plays an important role in the heterogeneous nucleation of ??-Mg grain. In the early stage of solidification, Al-Mn-C compound particles formed on the surface of Al₄C₃ nano-particles should be the potential nuclei for primary ??-Mg and probably responsible for the grain refinement achieved in the carbon inoculation process.