On the oxidation ofα-Fe andε-Fe2 N1−z II. Residual strains and blisters in the oxide layer

The development of residual strains in the iron-oxide layers growing on -Fe and -Fe₂N_1–z at 673 K in O₂ at 1 atm was investigated by X-ray diffraction at room temperature. After correction for thermal-strain development due to cooling after oxidation, it was found that tensile growth strains occur in magnetite and compressive growth strains occur in hematite. The growth strains in the oxides on -Fe are (in absolute sense) 2–3 times as large as those in the oxides on -Fe₂N_1–z. Buckling of the oxide layer occurs in the case of an -Fe substrate, which is attributed mainly to relaxation of the growth strains in magnetite and hematite. Thermal-strain development during cooling enhances the tendency for buckling. Buckling is not observed for oxide layers on -Fe₂N_1–z, which could be due to the smaller values of absolute strain in the oxide layer on -nitride. The absolute values of the growth strains in the oxide layer on -nitride being smaller is attributed to microstructural changes in the nitride layer during oxidation.     

The effect of pre-existing defects on the strength and deformation behavior of α-Fe nanopillars

The effects of two types of pre-existing defects, dislocations and clusters, on the strength and deformation behavior of body-centered cubic Fe nanopillars with a diameter of ～150 nm were investigated using in situ nanocompression in a transmission electron microscope. The plastic deformation of nanopillars containing high initial dislocation densities was observed to be relatively continuous, proceeding via a series of small- and intermediate-scale strain bursts that were associated with the movement/escape of dislocations and the formation of slip bands. Mechanical annealing was observed in nanopillars with high dislocation densities. When the dislocation density was reduced by in situ heating, the nanopillars were much stronger and the plastic deformation behavior transformed to a more abrupt and explosive mode. The introduction of a dispersion of solute atom clusters into nanopillars caused further strengthening as a higher stress level is required for dislocations to pass the clusters. The strengthening effect of cluster dispersion in nanopillars is comparable to that observed in the bulk steel. These phenomena are universal for Fe nanopillars with different crystallographic orientations.     

Application of the cluster variation method to ε-Fe2N1-z and ζ-Fe2N: ordering of interstitial atoms

The regular and the irregular trigonal prism approximations of the cluster variation method (CVM) are applied to investigate the ε-Fe₂N_1−z and the ζ-Fe₂N phases. The ε-Fe₂N_1-z/ζ-Fe₂N phase boundary, the types of interstitial ordering and the lattice parameters of the ε and ζ phases are calculated and compared with the available experimental data. In the composition range from 25 to 33 at.% N, long-range order occurs. The changes in the N distributions are associated with the strong repulsive interactions between neighbouring N atoms. The CVM results show that with increasing the N content towards 33 at.% N, the repulsive N–N interactions favour the distortion of the iron host lattice, thereby increasing the nearest-neighbouring distance between occupied sites, i.e. transformation to the ζ-Fe₂N phase. The calculated interstitial site occupations are in good agreement with those proposed on the basis of experimental data obtained by Mössbauer spectroscopy and neutron diffraction.     

Characterization and analysis of non-metallic inclusions in Ni42-Fe expansive alloy

Cracks and ruptures always occur during wire drawing process of 42% nickel-iron expansive alloy. In order to study the reasons of these phenomena, a method of metallographic observation in combination with sample electrolysis was used to characterize the non-metallic inclusions in the alloy wire. The results indicate that the inclusions in the alloy are oxidation products during the process of melting. There are single or complex phase inclusions composed of elements such as Al, Si, Ca, Ti, Fe, and O2. Among them, the macro-inclusions are TiO2 compound inclusions formed by the adhesion of Al and Si oxides on them. These inclusions are fragile ones with a low strain rate, as well as a rather high hardness, so that they are the main reason that leads to the surface cracks and ruptures in the alloy wires. The analysis has educed that the key point to enhance the product quality is to promote the cleanliness of the melt, control the types and quantity of non-metal inclusions in the alloy.     

Effects of Zr and Y on the Mechanical Properties and the Microstructure of Ti-Al-Sn-Nb-Mo-Si Alloy

In the present paper the effects of additions of Zr and Y on the microstructure and mechanical properties for Ti-(6.06.5)Al-(2.0～3.0)Sn-(1.5～6.0)Zr-(0.8～1.0)Mo-1.0Nb-0.25Si alloys are reported,The experimental results show that: with in-creasing of Zr content,tensile strength and creep resistance of the alloys increase,and reduction in area and thermal stability ofthe alloys decrease.Decrease in thermal stabiIity of the alloys mainly caused by surface thermal unstability.After heat treatmentY addition can make grain size of the alloys refine.The reduction in area and thermal stability of the alloys with Y addition areimproved,and tensile strength slightly decreases and creep resistance is essentially the same as the alloy without Y addition.Thesephenomena are explained in brief.     

On the reasons for the effects of dispersions of stable oxides and additions of reactive elements on the adhesion and growth-mechanisms of chromia and alumina scales-the “sulfur effect”

The sulfur effect theory proposes that elements such as sulfur segregate to the scale-metal interface, where they have a deleterious effect on scale-metal adhesion, and that reactive elements and dispersions of their oxides are beneficial because they prevent this segregation. Evidence in favor of this theory has been obtained by showing that the adhesion of the scale formed on chromium in 0.1 atm. oxygen at 950°C. is greatly improved if the chromium is annealed beforehand in hydrogen instead of in vacuo. It is shown that the theory can explain not only all the experimental observations regarding the beneficial effects of reactive elements and their oxides on scale-metal adhesion, but also their effects on scale growth-mechanisms.     

Preparation, Characterization and Photocatalytic Property of Cubic α-Fe2O3 Nanoparticles

设计了一种简单的水热合成法合成晶型可控的立方结构的α-Fe2O3,通过扫描电子显微镜,透射电子显微镜,和X射线衍射对所制备产物的结构和形态特征进行了分析。制备的立方结构的α-Fe2O3的尺寸范围在130~150 nm之间。研究结果表明,α-Fe2O3纳米材料作为一种有效的光催化剂,在过氧化氢存在的条件下可以用来光催化降解废水中的有机物（如罗丹明B）,这为设计和开发高效率可见光催化剂在去除工业废水中有机染料的应用提供了新的探索和基础。     

Evaluation of the corrosion and oxide microstructural characteristics of pure Zr and the Zr−1.5Nb alloy

The corrosion behavior and the oxide microstructural characteristics of pure Zr and the Zr-1.5Nb alloy were investigated. The crystalline structure and morphology of zirconium oxide formed in a water at 360°C and 18.9 MPa was analyzed using a High Voltage Electron Microscope (HVEM). The corrosion rate increased more in pure Zr than in the Zr-1.5Nb alloy after the transition of the corrosion rate. From a HVEM oxide analysis and an imaging process using the DigitalMicrograph^™ program for both oxides formed on pure Zr and the Zr−1.5Nb alloy, it was found that most of the oxide amorphology consisted of both equiaxed and columnar grains. They formed in the outer and middle region of the oxide layer and were identified as a monoclinic phase. However, a complex oxide structure formed near the metal/oxide interface in the Zr−1.5Nb alloy, which showed good corrosion resistance. Thus, this implies that the Nb affected the oxide characteristics of the crystal structure and changed the corrosion behavior.     

The Influence of Method of Carburizing and Nitrocarburizing on the Microstructure and Properties of Tool Steels

The paper presents the results of wear and metallography tests of tool steel grades: ASTM A681, ChI2M and Ch12FS per GOST, AMS 6437E i BS X46Cr13, all surface hardened by the Carbo process (carburizing) and by the NiCar process (nitrocarburizing). The therrno-chemical treatment was conducted in powder pack for a duration of 6 h (carburizing) and for 4 h in the case of nitrocarburizing. Factors investigated were: morphology, depth and microhardness of the cases obtained, their microstructure, as well as phase composition. Wear tests were conducted by the three cylinder-cone method.Wear velocity was 0.58 m/s, unit load was 50 MPa and 400Mpa, wear path was 3470 m. Oil SAE30 was applied at the rate of 30 drops per minute.     

Recrystallization and the possibility of the realization of the α-γ diffusionless transformation during the ultrarapid laser heating of steels

Analysis is given of phase and structural transformations occurring upon ultrarapid laser heating in steels with different initial structures, namely, after annealing, after preliminary quenching, quenching and tempering, and after quenching with subsequent deformation and tempering. It is shown that a significant suppression of diffusion processes occurs during laser heating; this circumstance substantially affects the nature of the phase and structural transformations proceeding during laser processing. Special attention is given to studying the process of recrystallization and to the phenomenon of structural heredity during laser heating. The process of recrystallization during laser heating is considered as consisting of two stages, namely, an ordered lattice rearrangement (α-γ transformation) and the recrystallization of austenite that suffered phase-transformation-induced hardening (“phase naklep”). The effect of tempering and plastic deformation on the recrystallization of a preliminarily quenched steel consists in the intensification of the second stage, i.e., of the recrystallization of the transformation-hardened austenite. It is shown that the α-γ transformation during the laser heating of steels with the initial structure of lath martensite occurs by the “mechanism of recovery,” i.e., via the formation and growth of austenite nuclei. In steels with the initial structure of pearlite, the nucleation of austenite during laser heating can occur by a shear martensite-like diffusionless mechanism with the observance of characteristic orientation relationships between the initial ferrite and the newly formed austenite.     

Effects of milling and crystallization conditions on microstructure of Nd2Fe14B/α-Fe powder

Effects of milling and crystallization conditions on microstructure,such as amorphous phase and nanocrystalline phase, were investigated by X-ray diffractometry(XRD),differential scanning calorimetry(DSC),and transmission electron microscopy (TEM),respectively.The results show that nanocomposite Nd2Fe14B/α-Fe powder can be prepared by mechanical milling in argon atmosphere and a subsequent vacuum annealing treatment.The grain sizes of both Nd2Fe14B andα-Fe phase decrease drastically with increasing milling time.After milling for 5 h,the as-milled material consists ofα-Fe nanocomposite phases with the grain size of 10 nm,and some amorphous phases,which can be turned into Nd2Fe14B/α-Fe nanocomposite phases by the subsequent annealing treatment.Milling energy of mechanical milling after 5 h by theoretical calculation is 6 154.25 kJ/g.     

Analysis of the Active Au Species on Au/α-Fe2O3 Catalyst

采用沉积沉淀法制备了CO低温氧化 Au/α-Fe2O3催化剂,利用 X 射线衍射(XRD)、X 射线光电子能谱(XPS)、BET 比表面测定、程序升温还原(H2-TPR)等表征技术,对比了制备过程 pH 值的微小变化、焙烧及光线照射对催化剂结构及催化性能的影响,探明了 Au/α-Fe2O3催化剂的活性物种。结果表明,110 ℃处理的 Au/α-Fe2O3催化剂表面同时存在 Au3+、Au0以及过渡态 Auδ+(0<δ<1),它们对 CO 氧化的活性顺序为 Au3+>Auδ+>Au0;pH 值为 8 条件下制备的催化剂 Au3+含量高、比表面积大,催化性能最好;高温焙烧使氧化态金还原的同时也使载体比表面积严重缩小,催化活性显著下降;紫外线照射可以引起 Au3+的逐渐还原以及 Au0 颗粒的生长,其催化失活作用弱于高温焙烧。     

Effect of the structure of the oxidized titanium surface on the particle size and properties of the deposited copper–molybdate catalyst

The parameters of wetting of oxide coatings on titanium formed by the method of plasma electrolytic oxidation (PEO) in an aqueous silicate electrolyte with subsequent deposition of a layer of TiO₂ nanoparticles and ultrasonic treatment by a polymer–salt gel including copper and molybdenum compounds have been investigated. The effect of the oxidized surface microrelief, TiO₂ nanoparticle layer, and pore shape and size on impregnation solution spreading and the structure of the copper–molybdenum catalytic coating formed at further thermal treatment has been demonstrated. Complex oxide composites with ultradispersed catalyst particle sizes characterized with high activity in oxidation of carbon black particles have been obtained.     

Stability,structure and electronic properties of γ-Fe23C6 from first-principles theory

First-principles’ calculations of GGA and GGA + U type have been performed for γ-Fe₂₃C₆, a complex iron carbide with 116 atom in the unit cell. GGA results were found to be in better agreement with experimental data than GGA + U results. Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored. Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities. The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in γ-Fe₂₃C₆. The lattice parameters of γ-Fe₂₃C₆ match those of austenite well. Surprisingly, pure γ-Fe₂₃C₆ is found to be more stable than commonly occurring θ-Fe₃C cementite. Moreover, the calculations show low vacancy energy (about 0.37 eV) for Fe at 4a sites in γ-Fe₂₃C₆. Conditions of formation and factors hampering the formation of γ-Fe₂₃C₆ in steel manufacturing processes are discussed.     

An analysis of the dynamic resistance and the instantaneous energy of the CO2 arc welding process

A self-developed welding dynamic arc wavelet analyzer was adopted to analyze and assess the welding process of two CO2 arc welding machines. The experimental results indicate that the instantaneous energy can reflect the influence of the welding current and voltage on dynamic arc characteristic synthetically. Through calculating and analyzing the instantaneous energy, the energy during arc ignition and short circuit in CO2 welding process can be confirmed rationally, thus the foundation for the accurate design and control of the welding current and voltage can be provided. By reducing the ripple disturbance of the dynamic resistance, avoiding peak current and voltage waveform,and enhancing the transition frequency of short circuit suitably, the stability of the welding arc and the weld appearance can be improved.     

Relationship between the types of binary alloy phase diagrams of Ⅷ and IB group elements and the Mendeleev numbers

The relationship between the types of binary alloy phase diagrams of VIII and IB group elements and the Mendeleev numbers was discussed for the first time using the VIII and IB group elements as solvent metals (A) and the other elements as solute metals (B), basesd on their alloy phase diagram types. The Mendeleev numbers of the solvent metals and the solute metals were expressed as MA and MB, respectively. A two-dimension map of MA/MB was drawn. It is indi-cated that there is an oblique line in the map, which divides the binary alloy phase diagram types of solvent metals intotwo symmetry parts, the phase diagram types of the other elements with solvent metals located at the above or down ofthe line respectively, while on the line, ΔM= 0. The phase diagrams between the solvent metals basically are simple systems, mainly belong to the types of continues solid solution and the peritectic (about 40% for each type). The solvent metals can be divided into three groups: Co, lr, Rh, Ni, Pt, and Pd as the first group; Ag, Au, and Cu as the second group;and Fe, Os, and Ru as the third group. The characteristics of the phase diagrams formed between the elements in each group were discussed. About 80% phase diagrams belong to complex systems and less than 20% belong to the simple systems. The regular variation of the chemical scale, the metallic radii of the atoms, the number of valence electrons, and the first ionization energy with the Mendeleev numbers and the crystal structure were introduced as well.     

Effect of high magnetic field on the crystallization of Nd2Fe14B/α-Fe nanocomposite magnets

Nd8.1Dy0.9Fe76.95Co8.55B5.5 nanocomposite magnets annealed with and without a 10 T magnetic field were investigated in this article. The ribbons with coexisting amorphous and crystalline phases were selected to do this study. The resuits of Moessbauer spectroscopy revealed that the content of α--Fe increased when annealed in high strength magnetic field. The size of the grains also increased considerably after the application of magnetic annealing. All these led to the decrease of the magnetic properties, especially the coercivity of the ribbons.     

Determination of the effective zero-point and the extraction of spherical nanoindentation stress–strain curves

In this paper, we present a novel approach to converting the load–displacement data measured in spherical nanoindentation into indentation stress–strain curves. This new method entails a new definition of the indentation strain, a new procedure for establishing the effective zero-load and zero-displacement point in the raw dataset, and the use of the continuous stiffness measurement (CSM) data. The concepts presented in this paper have been validated by finite element models as well as by the analysis of experimental measurements obtained on aluminum and tungsten samples. It is demonstrated that the new method presented in this paper produces indentation stress–strain curves that accurately capture the loading and unloading elastic moduli, the indentation yield points and the post-yield characteristics in the tested samples.     

Dependency of the thermal and electrical conductivity on temperatures and compositions of Zn in the Al−Zn alloys

The variations of thermal conductivity (K) with temperature for Al–xZn (x = 5, 10, 20, 30, 50 and 60 wt. %) alloys were measured by using a radial heat flow furnace. The variations of electrical conductivity (σ) of solid phases with temperature for the studied alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of K from the plots of K. The thermal temperature coefficient (α_TTC) and the electrical temperature coefficient (α_ETC) were obtained. Dependency of the α_TTC and α_ETC on the composition of Zn in the Al?Zn alloys was also investigated. According to the present experimental results, K of Al–Zn alloys linearly decrease with increasing temperatures up to the melting temperature for each composition and exponentially decrease with the increasing Zn content. On the other hand, the σ of Al based Al-Zn alloys exponentially decrease with increasing temperature and Zn content.