Evolution of microstructure and hardening,and the role of Al3Ti coarsening,during extended thermal treatment in mechanically alloyed Al-Ti-O based materials

Extruded rods of mechanically alloyed (MA) Al-0.25wt%C-10vol%TiO₂ (A1), Al-0.35wt%Li-1wt%Mg-0.25wt%C-10vol%TiO₂ (A2), and Al-0.35wt%Li-1wt%Mg-0.25wt%C-7.5vol%TiO₂ (A3) have been subjected to thermal treatments at 500°C, 550°C, 600°C, and 655°C for times up to 1500 h. At 550°C and 600°C, the materials displayed hardness increments, but the increase was highest for A1 (∼30 kg/mm²) due to fine Al₃Ti precipitation. The starting grain size of ∼0.5 μm in A1 showed virtually no increase even after 1500 h at 600°C. XRD and TEM indicated transformation of TiO₂ and TiO to Al₃Ti. Numerous “block-shaped” Al₂O₃ particles (α, δ, η, and γ polymorphs) were formed in A2 at 600°C. The α-Al₂O₃ particles exhibited some lattice matching with the α-Al matrix. An initially rapid Al₃Ti coarsening rate at 600°C in A1 was reduced significantly between 336 h and 1500 h. Dispersion strengthening by Al₃Ti and Al₂O₃ was mainly responsible for the maximum strength of A1 after heat treatment, while the Hall–Petch contribution was less significant, despite the fine grain size.     

Phase equilibria of Zn-Al-Ti ternary system at 450 and 600 °C

The phase relationships in the Zn-Al-Ti system at 450 and 600 °C were experimentally determined using equilibrated alloys method. The specimens were investigated by means of scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffractometry. Eleven and eight three-phase regions are confirmed in the 450 and 600 °C isothermal sections, respectively. The Ti₂Al₅ which only exists at high temperature (990-1199.4 °C) in Ti-Al binary system is confirmed in two isothermal sections due to the dissolution of zinc. The T phase is confirmed as a ternary compound rather than an extension phase of TiZn₃ at 450 °C. The T₂ phase is a new ternary phase stable at 450 and 600 °C in Zn-Al-Ti ternary system.     

Sintering of Fe2NiO4 with an internal binder: a way to obtain a very dense material

The coupled synthesis and sintering of Fe₂NiO₄ can be carried out from the calcination under air at high temperatures (>1200 °C) of precompacted (under 12 MPa) pellets of different mixtures: NiO/α-Fe₂O₃; NiO/α-Fe₂O₃/Fe; NiO/α-Fe₂O₃/Ni. The densest material is obtained at 1200 °C only from the following mixture: NiO (40 mol%), α-Fe₂O₃ (50 mol%) and Ni (10 mol%). Because the metallic nickel is very ductile, it is used as an internal binder in order to enhance the precompacting of the samples. Moreover, the role of nickel is to enhance the sintering reaction. This route leads to a final material of relative density close to 98±2%.     

Preparation and magnetic properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> microtubules prepared by sol-gel template method

Fe(OH)₃ precursor sol was prepared by a sol-gel method. The precursor sol was dipped onto the absorbent cotton, and gel was formed on the absorbent cotton template after the volatilization of moisture. Fe₂O₃ microtubules were synthesized after the process of self-propagation or calcination. The phase, morphology, and particle diameter of the samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the magnetic properties of the samples were measured using a vibrating sample magnetometer (VSM). The external diameters of Fe₂O₃ microtubules ranged between 8 and 13 μm, and the wall thicknesses ranged between 0.5 and 2 μm. The type of the calcination method plays a significant role in developing the Fe₂O₃ phase and the variation in the magnetic properties in the sol-gel template complexing method. γ-Fe₂O₃ was synthesized by a self-propagation method. However, α-Fe₂O₃ was synthesized after calcination at 400°C for 2 h. The coercivity of the samples synthesized by calcination at 400°C for 2 h after self-propagation was found to increase significantly, thereby presenting hard magnetic properties.     

Identification of corrosion products resulting from accelerated oxidation process

Abstract

Scanning electron microscopy analysis, X-ray powder diffraction and room temperature ⁵⁷Fe Mössbauer spectroscopy were used to identify the corrosion products of uncoated and coated low alloy steels (LAS) and low carbon steels (LCS) resulting from an accelerated steam oxidation test for 180 h at 660°C. From the Mössbauer spectral analysis, it was shown that in all cases, a series of iron compounds such as α-Fe₂O₃, Fe₃O₄, γ-Fe₂O₃, δ-FeOOH, α-FeOOH, Fe(OH)₂ and Fe(OH)₃ were formed, while XRD measurements revealed only the α-Fe₂O₃ and/or Fe₃O₄/γ-Fe₂O₃ phases. In the LAS uncoated sample, an amorphous phase with magnetic features is found. In the spectra of the borided samples and of the uncoated LCS, an additional doublet was observed, which reveals the presence of a superparamagnetic phase. From the relative areas of the subspectra, it is concluded that the boron aluminised sample underwent the lowest degradation. The mechanism proposed for corrosion products formation is based on the dissociation process.     

Phase equilibria of Co−Mo−Zn ternary system

To experimentally determine the isothermal sections of Co−Mo−Zn ternary system at 600 and 450 °C, the equilibrated alloy and diffusion couple methods were adopted by using scanning electron microscopy coupled with energy-dispersive spectrometry, X-ray diffractometry and electron probe microanalysis. Experimental results show that there are six three-phase regions on the Co−Mo−Zn isothermal section at 600 °C and nine three-phase regions on the Co−Mo−Zn isothermal section at 450 °C. No ternary compound is found in these two isothermal sections. Both the maximum solubilities of Mo in the Co−Zn compounds (γ-Co₅Zn₂₁, γ₁-CoZn₇, γ₂-CoZn₁₃ and β₁-CoZn) and that of Zn in ε-Co₃Mo are no more than 1.5 at.%. The maximum solubilities of Zn in μ-Co₇Mo₆ are determined to be 2.1 at.% and 2.7 at.% at 600 and 450 °C, respectively. In addition, the maximum solubilities of Co in MoZn₇ and MoZn₂₂ are 0.5 at.% and 4.7 at.% at 450 °C, respectively.     

硼化物原位自生增强TiAl基复合材料的组织演化、热变形行为及加工工艺设计（英文）

硼元素添加造成的相转变和硼化物析出等因素会对原位TiAl基复合材料显微组织演化及热变形行为产生影响。利用等温压缩实验、扫描电子显微技术以及透射电子显微技术等研究材料的动态再结晶和动态回复机制,并计算出其表现变形激活能为691.506 k J/mol。在1100～1200℃温度区间,再结晶γ和α晶粒的形核长大分别主导α₂→α相转变温度上、下的热变形行为。α相的动态回复主导材料在1250℃低应变速率下的热变形行为;同时,硼元素会提高α相含量,降低γ→α和α₂→α相转变温度,进而促进加载过程中回复α相晶粒的形核长大。根据新建的本构模型,对TiAl基复合材料的变形机制和加工工艺进行详细阐述.     

A transmission electron microscope study of hydrothermally synthesized yttrium disilicate powders

The crystallization of three hydrothermally synthesized Y₂Si₂O₇ precursor powders at temperatures between 991 and 1038°C has been studied using transmission electron microscopy. Powders prepared in acidic or near-neutral conditions were found to be highly inhomogeneous both chemically and microstructurally, with a wide range of crystalline phases formed. In contrast to this, a powder prepared in alkaline conditions was found to be very homogeneous. Small crystalline nuclei were formed in this powder on heating to 1006°C which grew rapidly at 1038°C to form large single crystal particles. The majority of these had the α-Y₂Si₂O₇ phase but some were of the y-Y₂Si₂O₇ phase. The reasons for the formation of this y-phase are unclear, although it would be expected to transform to α-Y₂Si₂O₇ on further heat treatment at 1200°C. Weaknesses in the current crystal structure data for yttrium disilicate phases are identified and suggestions made for rectifying them.     

High-temperature oxidation of Permalloy in air

Hematite (α-Fe₂O₃) nanowires were observed through directly annealing Ni₈₁Fe₁₉ foils at 600 °C for 120 min in atmosphere. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterise the nanowires. The results indicate that the growing mechanism includes iron segregation to the surface combined with an internal stress induced by the oxidation process.     

450 °C and 600 °C Isothermal Sections of the Zn-Cr-Si Ternary Phase Diagram

The 450 and 600 °C isothermal sections of the Zn-Cr-Si system were experimentally constructed using scanning electron microscopy equipped with energy dispersive x-ray spectrometry, and x-ray diffraction. Six three-phase regions in the 450 °C section and five three-phase regions in the 600 °C section were identified experimentally. No ternary compound was found. Si has low solubility in CrZn₁₇. The Zn solubility in CrSi₂, Cr₅Si₃, and Cr₃Si are all less than 2.2 at.%. The CrSi phase cannot be in equilibrium with the η-Zn phase. Thermodynamic extrapolation of the Zn-Cr-Si system was carried out and showed good agreement with experimentally determined phase relationships.     

Effect of crystallization temperature on microstructure and ferroelectric property of Bi3.25 Eu0.75 Ti3O12 thin films prepared by MOD method

1 Introduction Many researches have been done on candidates in ferroelectric material for non-volatile random access memories applications. Among them, lead zirconate titanate(PZT) thin films have been widely studied because they have many advantages such…     

Phase transformation behavior of Al9(Mn,Ni)2 eutectic phase during heat treatment at 600 °C in Al-4Ni-2Mn alloy

The morphology evolution and phase transformation of Al₉(Mn,Ni)₂ eutectic phase in an Al-4Ni-2Mn alloy during heat treatment at 600 °C were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that nearly all of the eutectic fibers change into prolate ellipsoid and spherical particles in the process of heat treatment, and Ostwald ripening phenomenon occurs in the eutectic region with the increase of the heat treatment time. Besides, a phase transformation from Al₉(Mn,Ni)₂ to O-phase is confirmed. The morphologies of the transformed particles indicate that the O-phase preferentially nucleates on the specific crystal plane of the Al₉(Mn,Ni)₂ eutectic phase and grows in a certain direction. During the phase transformation, the (010)[001] slip system in O-phase is activated, and the resultant slip traces appear on the surface of some O-phase particles.     

Synthesis of Pd/α-Fe2O3 nanocomposites for catalytic CO oxidation

Iron oxide and metal doped iron oxide nanocomposites have found attractive and versatile applications in many research areas such as catalysts, sensors, and biomedicine. This work reports a surfactant-free hydrolysis approach for the synthesis of hematite (α-Fe₂O₃) and Pd doped α-Fe₂O₃ nanoparticles with low-temperature catalytic activity. By this method, iron oxide rod-like nanoparticles were achieved by hydrolysis of ferric chloride salt with dilute HCl at a temperature of 100 °C. The Pd/iron oxide nanocomposites were obtained by adding citric acid into a mixture of iron oxide nanoparticles and palladium precursor (Pd(CH₃CN)₂Cl₂) under a reflux heating at 90 °C for 2 h. This method is featured as no use of any surfactants and templates, and no requirement of high-temperature thermal decomposition that are usually required for shape/size control in polar or nonpolar solvents. More importantly, it was found that the Pd/α-Fe₂O₃ nanocomposites exhibited high low-temperature catalytic activity in carbon monoxide (CO) oxidation.     

Precipitation in Fe–15Cr–1Nb alloys after oxygenation

The effect of O on the phase relations at 950 °C in Fe–15Cr–1Nb alloys is experimentally investigated. Fe–15Cr–1Nb alloys are oxygenated by subjecting high-purity Fe–15Cr–1Nb to an O atmosphere at 600 °C. Both the high-purity and the oxygenated Fe–15Cr–1Nb alloys are heat treated for up to 500 h at 950 °C, quenched and investigated by scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. The results show that Fe₂Nb is in equilibrium with α (Fe, Cr) with 0.29 at.% Nb in solid solution in the pure Fe–15Cr–1Nb alloy. The presence of a small amount of O induces the precipitation of a Fe₆Nb₆O_x phase with a cubic crystal structure and lattice parameter 1.13 nm, thereby decreasing the Nb in solid solution in α (Fe, Cr) with increasing O content.     

Oxidation behavior and mechanism of porous nickel-based alloy between 850 and 1000 °C

The oxidation behavior and mechanism of a porous Ni–Cr–Al–Fe alloy in the temperature range from 850 to 1000 °C were investigated by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analyses and X-ray photoelectron spectroscopy (XPS). The results show that the oxidation kinetics at 950 and 1000 °C of this porous alloy is pseudo-parabolic type. Complex layers composed of external Cr₂O₃/NiCr₂O₄ and internal α-Al₂O₃ are formed on the surface of the oxidized porous alloys. γ' phases favor the formation of NiO/Cr₂O₃/NiCr₂O₄ during the initial oxidation. Many fast diffusion paths contribute to the development of the oxide layers. The decrease of the open porosity and the permeability with exposure time extending and temperature increasing can be controlled within a certain range.     

Nanocrystalline LiMn2O4 thin film cathode material prepared by polymer spray pyrolysis method for Li-ion battery

Nanocrystalline cubic spinel lithium manganese oxide thin film was prepared by a polymer spray pyrolysis method using lithium acetate and manganese acetate precursor solution and polyethylene glycol-4000 as a polymeric binder. The substrate temperature was selected from the thermogravimetric analysis by finding the complete crystallization temperature of LiMn₂O₄ precursor sample. The deposited LiMn₂O₄ thin films were annealed at 450, 500 and 600 °C for 30 min. The thin film annealed at 600 °C was found to be the sufficient temperature to form high phase pure nanocrystalline LiMn₂O₄ thin film. The formation of cubic spinel thin film was confirmed by X-ray diffraction study. Scanning electron microscopy and atomic force microscopy analysis revealed that the thin film annealed at 600 °C was found to be nanocrystalline in nature and the surface of the films were uniform without any crack. The electrochemical charge/discharge studies of the prepared LiMn₂O₄ film was found to be better compared to the conventional spray pyrolysed thin film material.     

Effects of heat treatment on phase contents and mechanical properties of infiltrated B4C/2024Al composites

The B₄C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical properties testing. The results show that phases of B₄C/2024Al composites include B₄C, Al, Al₃BC, AlB₂ and Al₂Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 °C for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 °C for 36 h does best to hardness of the composites, while at 700 °C for 36 h it is the most beneficial to their comprehensive mechanical properties.     

Mechanism and kinetics of iron extraction from high silica boehmite–kaolinite bauxite by hydrochloric acid leaching

The chemical and mineral compositions of bauxite recovered from the Severoonezhsk Bauxite Mine (Arkhangelsk region, Russia) were studied by XRD, ICP-OES, TG/DSC, SEM, TEM, and Mössbauer spectroscopy. The iron-containing minerals of the bauxites were found to comprise alumogoethite (α-Fe_1–xAl_xOOH), alumohematite (α-(Fe_1–xAl_x)₂O₃), alumoakaganeite (β-Fe_1–xAl_xO(OH,Cl)), and chromite (FeCr₂O₄). The efficiency of Fe extraction from the bauxite by HCl leaching was 82.5% at 100 °C, HCl concentration of 10%, solid/liquid ratio of 1:10, and the process duration of 60 min, with aluminum loss from the bauxites below 4.5% of the total Al contents in the bauxite. Analysis of the kinetics of the iron leaching process proved diffusion to be the limiting stage of the process at 90–100 °C. Bauxite residue after leaching presented traces of α-Fe_1–xAl_xOOH and β-Fe_1–xAl_xO(OH,Cl), and most of the iron content was in the FeCr₂O₄. In bauxite residue after HCl leaching, in addition to iron oxide, the contents of chromium and calcium oxides significantly decreased. The iron chloride liquor after leaching contained the rare earth elements (REE) of 6.8 mg/L Sc, 4.1 mg/L Ce and 2.3 mg/L Ga.     

Preparation and characterization of carbonyl iron soft magnetic composites with magnesioferrite insulating coating layer

Spherical carbonyl iron (Fe) powders were coated with magnesioferrite (MgFe₂O₄) insulating coating layer and then mixed with epoxy-modified silicone resin (ESR). Soft magnetic composites (SMCs) were fabricated by compaction of the coated powders and annealing treatment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the MgFe₂O₄ layer was coated on the surface of the iron powders. The magnetic properties of SMCs were determined using a vibrating sample magnetometer and an auto testing system for magnetic materials. The results showed that the SMCs prepared at 800 MPa and 550 °C exhibited a significant core loss of 167.5 W/kg at 100 kHz and 50 mT.     

Ferroelectric properties of dysprosium-doped Bi4Ti3O12 thin films crystallized in various atmospheres

Dysprosium-doped Bi4Ti3O12 （Bi3.4Dy0.6Ti3O12, BDT） ferroelectric thin films were deposited on Pt（111）/Ti/SiO2/Si（111） substrates by chemical solution deposition （CSD） and crystallized in nitrogen, air and oxygen atmospheres, respectively. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. The results show that the crystallization atmosphere has significant effect on determining the crystallization and ferroelectric properties of the BDT films. The film crystallized in nitrogen at a relatively low temperature of 650 ℃, exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr = 24.9 ℃/cm^2 and a coercive field of 144.5 kV/cm. While the films annealed in air and oxygen at 650 ℃ do not show good crystallinity and ferroelectricity until they are annealed at 700 ℃. The structure evolution and ferroelectric properties of BDT thin films annealed under different temperatures （600-750 ℃） were also investigated. The crystallinity of the BDT films is improved and the average grain size increases when the annealing temperature increases from 600 ℃ to 750 ℃ at an interval of 50 ℃. However, the polarization of the films is not monotonous function of the annealing temperature.