Characterization of a laser‐nitrided titanium alloy by electron backscattered diffraction and electron probe microanalysis

After a laser gas nitriding treatment of the Ti‐7.5Al (atom %) titanium‐based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or ‘coarse’ needles morphology, fixed into a α′‐Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the α′‐Ti matrix (up to 2–3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti₇₉N₁₇Al₄ chemical composition. Copyright © 2005 John Wiley & Sons, Ltd.     

The ternary system titanium-aluminum-nitrogen

The phase equilibria in the ternary system titanium-aluminum-nitrogen are investigated for two isothermal sections. At 1273 K one encounters the H-phase Ti₂AlN (a = 0.29912 nm, c = 1.3621 nm) and the cubic perovskite-type phase Ti₃AlN (a = 0.41120 nm). At 1573 K one encounters additionally Ti₃Al₂N₂ (space group: P31c, hexagonal axes a = 0.29875 nm, c = 2.3350 nm). α-Titanium dissolves nitrogen and aluminum to a large extent, but no solubility of the third element was detected in any of the other binary phases.     

Synthesis,characterization, and 2,4-dichlorophenoxyacetic acid degradation on In-Na<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> sol–gel prepared photocatalysts

Indium-Na₂Ti₆O₁₃ doped semiconductors were prepared by the sol–gel method using titanium and sodium alkoxides as precursors. The gelled samples were annealed at 700 °C for 4, 6, and 8 h, and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and UV–Vis diffused reflectance spectroscopy (DRS). XRD patterns of the samples show the formation of the Na₂Ti₆O₁₃ phase, whose crystallinity depends on the annealing time. The band gap calculated from the UV–Vis Kubelka–Munk function report similar values (3.2–3.4 eV) for all of the samples annealed at different times. SEM observations of the semiconductors showed microfiber bundle morphologies of about 5 μm. Meanwhile, by EDS analysis, indium oxide highly homogeneously dispersed on the hexatitanate surface was identified. The evaluation of the In-Na₂Ti₆O₁₃ semiconductors in the 2,4-dichlorophenoxyacetic acid (2,4-D) photodecomposition using ultraviolet light (λ = 254 nm) irradiation show that the photoactivity of the solids depends on the annealing time applied to the samples. The role of indium oxide is related to the indium oxide dispersed on the surface of the titanate diminishing the electron-hole recombination rate.     

X-Ray and Electron Microscopy Studies of Rare-Earth Tungsten Bronzes

Rare-earth tungsten bronzes, RE_xWO₃, of perovskite tungsten-bronze (PTB) type, formed by conventional solid-state synthesis, have been studied by X-ray powder diffraction, electron diffraction in combination with microanalysis, and high-resolution transmission electron microscopy (HRTEM). The X-ray patterns indicated cubic PTB type structure with a≈3.83 Å (subcell), while the electron microscopy study indicated a lowering of the subcell symmetry and a complex superstructure. The upper phase composition limit, x≤0.25, for the RE_xWO₃ bronzes with PTB-related structures was established from the microanalysis study. Ordered, disordered and microtwinned superstructures were revealed by electron diffraction patterns and HRTEM images taken along 〈110〉_p. The superstructure is due to filling of the interstices in the WO₃ structure with the rare-earth ions. A hypothetical model of the superstructure based on the contrast features in the HRTEM images has been deduced. The relationships between the RE_xWO₃ bronzes formed by solid-state synthesis under high- and ambient-pressure conditions are presented.     

Analytical Electron Microscopy of a Magnesium Alloy Containing Neodymium

 Microstructure and phase composition studies of QE-22 magnesium based alloy with 2–3% Ag, 1.8–2.5% Nd and min. 0.4% Zr, before and after full heat treatment have been carried out using various electron microscopy techniques like EDX mapping, line scans and TEM with SAED. An extrapolation technique enabled to eliminate the influence of Mg-matrix on the quantitative analysis results and allowed to estimate the composition of the second phase which was mostly (Mg, Ag)₁₂Nd type in the as cast alloy and (Mg, Ag)₁₂Nd and Mg₁₂Nd₂Ag equilibrium precipitates after the precipitation process.     

Synthesis and morphology of Ba(Zr<Subscript>0.20</Subscript>Ti<Subscript>0.80</Subscript>)O<Subscript>3</Subscript> powders obtained by sol–gel method

Barium zirconate titanate, Ba(Zr_0.20Ti_0.80)O₃ (BZT) powders were prepared by sol–gel method. These powders were characterized by thermogravimetric and differential thermogravimetric analyses (TG-DTA), X-ray diffraction (XRD) and microcopy electron transmission (TEM). The decomposition of the precursors was monitored by TG-DTA. XRD patterns reveal that BZT powders heat treated at 800 °C present single phase with perovskite-type cubic structure. TEM micrographs were employed to estimate the average particle size of the BZT powders (≈ 20 nm). The results indicate that the particle size of the BZT powders increases with the increasing of the holding time and aging temperature. The low aging temperature can reduce the agglomeration of the nanopowders. Three polyalcohols were employed as surfactants in sol–gel method: butanol (BTOL), polyethylene glycol (PEG) and polyvinyl alcohol (PVA). It is noted that PEG has a better effect on reducing agglomeration of BZT powders than that of the BTOL and PVA.     

The role of the interface in a Ti‐based metallic glass matrix composite with in situ dendrite reinforcement

Many in situ metallic glass matrix (MGM) composites have been developed as promising engineering materials having distinguished properties because of sharing virtues of high strength of metallic glasses and large plasticity of crystal phase, for example, Ti₄₇Zr₁₉Be₁₅V₁₂Cu₇ MGM composites (the yield strength: 1600 MPa, the fracture strength: 3024 MPa and the total strain 32.6%). Although the toughening mechanisms in these materials have been investigated, the role of the interface bridging the ductile dendrite and the glass phase is still unclear. To this aim, specimens of the as‐received and after compression of this Ti‐based MGM composite were investigated to by using the transmission electron microscopy and the high‐resolution transmission electron microscopy. The results of the microstructure investigation indicated that the interface in the composite consists of a nanosized transform layer with an approximate width of 4 nm. During plastic deformation, the interface either suppresses plastic deformation caused by dislocations on the dendrite side or initiates nucleation of multiple shear bands throughout nanocrystallization on the glass phase side nearby the interface, which is favorable for the plastic deformation of the material. Copyright © 2014 John Wiley & Sons, Ltd.     

Electron microscope study of alkoxide-derived compositions within the PbZrO3-PbTiO3 phase diagram

Pb(Zr_0.50Ti_0.50)O₃ solid solution was prepared using lead acetate and transition metal n-propoxides in n-propanol or n-butoxides in n-butanol. The complex solutions were hydrolysed with an excess of H₂O. The resultant powders were calcined up to 700°C for 30 minutes in a flowing oxygen atmosphere. Scanning electron microscope analysis showed different morphologies of the resultant powders. The n-propoxide derived powder consisted of gel fragments, while the n-butoxide derived one had agglomerated submicrometre particles. EDS analysis of the powders revealed no chemical heterogeneities in the examined samples upon calcining up to 600°C, notwithstanding the type of precursor used. Both samples, calcined at 700°C, exhibited a slight deficiency of lead in the pyrochlore type phase as compared to the perovskite phase.     

Fine tuning of gadolinium doped ceria electrolyte nanoparticles via reverse microemulsion process

Gadolinium doped ceria (Gd–CeO₂) nanoparticles have been synthesized by an reverse microemulsion system using cyclohexane as the oil phase, a non-ionic surfactant Igepal CO 520 and their mixed aqueous solutions of gadolinium III nitrate hexahydrate and cerium III nitrate hexahydrate as the water phase. The control of particle size was achieved by varying the water to surfactant molar ratio. The synthesized and calcined powders were characterized by thermogravimetry-differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The XRD results show that all the samples calcined at 700 °C were single phase cubic fluorite structure. The average size of the particle was found to increase with increase in water to surfactant molar ratio (R). The mean diameter of the particle for various value of R varies between 8–15 nm (SEM) and 7.5–11 nm (TEM), respectively. EDS confirm the presence of gadolinia and ceria phase in the nanopowder calcined at 700 °C. FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and calcined powder. Raman spectroscopy and DTA evidenced the formation of a solid solution of gadolinium doped ceria at room temperature.     

Facile solvent-free synthesis of pure-phased AlN nanowhiskers at a low temperature

Pure hexagonal aluminum nitride (AlN) nanowhiskers have been successfully synthesized by directly reacting AlCl₃ with NaN₃ in non-solvent system at the low temperature of 450 °C for 24 h. The obtained products are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction, which show that the obtained products are hexagonal phase AlN nanowhiskers with width from 10 to 80 nm and length up to several micrometers. The influencing factors of the formation of AlN nanowhiskers were discussed and a possible growth mechanism for AlN nanowhiskers was proposed. Additionally, the study on the corresponding optical properties and catalytic properties is also carried out.     

Electron Probe Microanalysis of Nitrogen in Glasses and Glass Ceramics

 A homogeneous (phosphate glass) and a heterogeneous (glass ceramic) material were chosen to develop a method for electron microprobe analysis of nitrogen in glasses and glass ceramics. The metaphosphate (50 mole-% P₂O₅, 25 mole-% BaO, 25 mole-% Rb₂O) base glass and the silicate glass (composition of the base glass: 6.9 mole-% Al₂O₃, 21.3 mole-% MgO, 47.3 mole-% SiO₂, 5.1 mole-% CaO, 19.4 mole-% AlN) were melted and cooled down to room temperature. In a second step, the two materials were nitrided by applying dry NH₃ in a special tube furnace. Up to 5 wt.-% of nitrogen could be introduced. The ability of energy dispersive (EDX) as well as wavelength dispersive (WDX) electron probe microanalysis to analyze low contents of light elements in combination with highly concentrated heavy elements was tested both for glasses and for glass ceramics. Measuring conditions had to be optimized to get reliable analytical results as well as to avoid radiation damage of the glasses which may occur especially in the case of wavelength dispersive X-ray analysis. The results were compared with two different analytical methods: inductive coupled plasma analysis and a commercial nitrogen-oxygen-analyzer (the specimen is decomposed by heating and the released gases are analyzed spectroscopically (O) and electrically (N)).     

Phase relations in the Nb–Ni–Cr system at 1,100?°C

Abstract  

The isothermal cross section through the ternary phase diagram Nb–Ni–Cr at 1,100 °C was constructed by means of diffusion couples and equilibrated alloys. It was found that nearly 28 at.% of Cr can be dissolved in the μ phase (Nb₇Ni₆) at this temperature, and the solubility of chromium in NbNi₃ is approximately 5 at.%. Under these circumstances the low-temperature (cubic) modification of the NbCr₂ Laves phase can dissolve up to 6 at.% of nickel, but further increase of the Ni content (up to approximately 10 at.%) stabilizes the hexagonal (high-temperature) modification of the Laves phase. The presence of this pseudo-ternary compound which is in equilibrium with all binary intermetallics and body-centred cubic (BCC) Nb- and Cr-based solid solutions largely determines the topology of the isotherm at 1,100 °C. The formation of this phase was also observed in the reaction zone between Nb and Ni–Cr solid solution when chromium concentration exceeded 15 at.%.     

Interface microstructure and diffusion kinetics in diffusion bonded Mg/Al joint

The interface microstructure, formation of diffusion bonded joint and regulation of atom diffusion were studied by means of scanning electron microscope (SEM), energy dispersion spectroscopy (EDS) and electron probe microanalyser (EPMA). The experimental results indicated that an obvious interfacial transition zone was formed between Mg and Al, and there are three intermetallic layers Mg₁₇Al₁₂, MgAl and Mg₂Al₃ in this zone. Diffusion activation energy of Mg and Al in the above layers was lower than that in the Mg and Al base metals. The thickness (x) of each layer can be expressed as x ² = 4.14exp(−28780/RT)(t−t ₀), x ² = 31.4exp(−25550/RT)(t−t ₀) and x ² = 0.6exp(−22600/RT)(t−t ₀) corresponding to Mg₁₇Al₁₂, MgAl and Mg₂Al₃ with heating temperature (T) and holding time (t).     

Ni添加对0.4Zr0.1V1.1Mn0.5Cr0.1合金的相结构和电化学性能的影响

本文通过XRD、SEM、EDS研究了Ti_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1Ni_x(x=0，0.2，0.4，0.6，0.8)合金的相结构和电化学性能。该合金系由BCC结构的V基固溶体主相和六方结构的C14 Laves第二相组成，Ni能够促进第二相的生成，Ni含量的增加导致了各相中的化学组成和晶格参数的变化，并通过电化学方法研究了Ni含量对_0.4Zr_0.1V_1.1Mn_0.5Cr_0.1合金电极的最大放电容量、自放电性能、高倍率放电性能、循环稳定性能等的影响。     

Atomic Mechanism of Predictable Phase Transition in Dual‐Phase H2Ti3O7/TiO2 (B) Nanofiber: An In Situ Heating TEM Investigation

The phase transition from H₂Ti₃O₇ to TiO₂ (B) in a 1D single nanocrystal of H₂Ti₃O₇ was observed by in situ heating in a transmission electron microscope experimentally. The results indicate a typical monoclinic‐to‐monoclinic crystallographic orientation relationship between the two phases. Moreover, the fundamental building blocks and invariant deformation element model were both adopted to reveal the atomic mechanism and predict the crystallographic orientation relationship quantitatively for the phase transition. The prediction was precisely consistent with TEM results.     

Synthesis and electrochemical properties of spinel Li4Ti5O12−x Cl x anode materials for lithium-ion batteries

Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were synthesized successfully via high temperature solid-state reaction. X-ray diffraction and scanning electron microscopy were used to characterize their structure and morphology. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge cycling performance tests were used to characterize their electrochemical properties. The results showed that the Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were well-crystallized pure spinel phase and that the grain sizes of the samples were about 3–8 μm. The Li₄Ti₅O_11.8Cl_0.2 sample presented the best discharge capacity among all the samples and showed better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂. When the discharge rate was 0.5 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the superior discharge capacity of 148.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was 129.8 mAh g⁻¹; when the discharge rate was 2 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the discharge capacity of 120.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was only 89.8 mAh g⁻¹.     

Dielectric properties of Ni-doped Ba0.5Sr0.5TiO3 ceramics prepared with hydrothermal synthesized nanopowders

Ba_0.5Sr_0.5Ti_1?xNi_xO₃ (BSTN) ceramics were prepared from BSTN nanopowders synthesized by a hydrothermal method. The phase and microstructure of samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy. XRD results indicate a cubic structure of the pure BST nanopowders. The cubic structure can be converted to the orthorhombic phase with increasing of Ni content to x = 0.01 and returned to the cubic structure with the presence of Ni(OH)₂ impurity phase for x = 0.03 and 0.05. However, the BSTN ceramics sintered at 1,200 °C for 3 h revealed the orthorhombic phase structure with NiO impurity phase for all Ni content. The doping of Ni in Ba_0.5Sr_0.5TiO₃ structure can increase the grain size of samples from 1.47 to 3.26 μm. The dielectric constant, loss tangent (tanδ) and phase transition temperature of BSTN ceramics were reduced with increasing Ni content.     

Single crystals of the filled Ti2N‐type η‐phase Ti3Zn3Ox (x = 1.07 and 1.23) prepared using a Bi flux

Single crystals of the filled Ti₂Ni‐type Ti₃Zn₃O_x η‐phase (cubic, space group Fdm) having {111} facets were obtained by heating Ti, Zn and ZnO with a Bi flux. The lattice parameter of a single crystal prepared at 800°C was 11.4990 (2) Å, which is close to that of Ti₃Zn₃O_∼0.5 (a = 11.502 Å), as reported by Rogl & Nowotny [Monatsh. Chem. (1977), 108 , 1167–1180]. The occupancies of the O1 (16c) and O2 (8a) sites were 1 and 0.071 (12), respectively, and the composition of the crystal was determined to be Ti₃Zn₃O_1.04. A single crystal from the sample prepared at 650°C had the same structure type, with a lattice parameter of 11.5286 (2) Å. However, O atoms were situated at a new 32e site in addition to the original 16c and 8a sites, and the Zn‐atom positions were split in accordance with the new O‐atom site. The chemical formula Ti₃Zn₃O_1.27 determined by X‐ray diffraction occupancy refinement agreed with the chemical composition obtained for the cross section of the single crystal determined with an electron probe microanalyzer.     

Microstructure analysis of a bronze–steel electron beam weld

An electron beam welded joint of bronze and steel has been investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The phases and the resulting microstructure in the different zones of the joint have been characterised in detail and compared to hardness. The fine grained microstructure of the weld zone is partly dominated by the directed solidification of the melt. It mainly consists of the α-copper solid solution phase, the intermetallic δ phase Cu₃₁>Sn₈> as well as the bainitic and the martensitic steel phase. This mixture results in a considerably increase in hardness compared to base materials. The heat affected zone of bronze shows a refinement of the used dendritic cast material in a very small area. In the heat affected zone of the mild steel the change of microstructure depends on the distance from the weld zone due to the influence of thermal energy impact and heat dissipation. A maximum of hardness is reached nearby the weld due to the formation of bainite and martensite. The resulting hardness profile is asymmetrical.     

Structural dependence of non-linear optical properties of 4-Dimethylamino-3-cyanobiphenyl

 4-Dimethylamino-3-cyanobiphenyl (4-DMA-3-CB) was characterized with respect to linear and nonlinear optical properties in a crystal as well as in solution. The crystal structure was studied dependent on the crystallization conditions. It is shown that the crystal structure exhibiting NLO-activity can completely be solved by a combination of electron diffraction and computer modeling. There are four molecules per unit cell in the space group Pna2₁ with dimensions a=10.28 Å, b=22.64 Å, c=5.27 Å. From this model structure the values and orientation of the dipole μ and static second order polarizability β can be calculated. Their relevance to the values obtained by a combination of polarization dependent measurements of Electric Field Induced Second Harmonic Generation (EFISH) and Hyper-Rayleigh-Scattering (HRS) in solution are discussed. The molecular second order polarizability tensor was found to be dominated by one single component. The orientations of the dipole and the vectorial parts of the second order polarizability delivered by the semiempirical calculations are in good agreement with the results of the EFISH and HRS-measurements and allow a deeper insight into the nonlinear optical properties of the crystal. Received: 15 April 1996 Accepted: 21 June 1996