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1.
The internal friction δ, exchange integral A, magnetocrystalline anisotropic constant KI and saturation magnetization Ms of Fe–Cr–Al and Fe–Cr–Al–Si alloys annealed at 1373 and 1473 K are measured. The energy density and volume fraction of domain walls (DWs) of these alloys are calculated based on the theories of ferromagnetism and the magnetic parameters measured. The physical process of irreversible movement of 90° DWs is suggested. The results indicate the dissipated elastic energy per unit volume due to the irreversible movements of 90° DWs is equal in value to the energy density of DWs, that is γ w/δ w=λ sE/ 2. It is an effect of magneto-elastic interchange in ferromagnetic alloys. 相似文献
2.
We consider a Ginzburg-Landau model free energy F(ε, e1, e2) for a (2D) martensitic transition, that provides a unified understanding of varied twin/tweed textures. Here F is a triple well potential in the rectangular strain (ε) order parameter and quadratic e12, e22 in the compressional and shear strains, respectively. Random compositional fluctuations η( r) (e.g. in an alloy) are gradient-coupled to ε, ˜ − ∑ rε( r)[(Δ x2 − Δ y2)η( r)] in a “local-stress” model. We find that the compatibility condition (linking tensor components ε( r) and e1( r), e2( r)), together with local variations such as interfaces or η( r) fluctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective ε-ε interactions. We have carried out extensive relaxational computer simulations using the time-dependent Ginzburg-Landau (TDGL) equation that supports our analytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and Fe xPd 1 − x alloys can be explained on the basis of our analysis and simulations. 相似文献
3.
Segregation of yttrium induces the formation of Y 0.25Zr 0.75O 2-x and Y 0.5Zr 0.5O 2-y microdomains, with L1 2- and L1 0-like ordered structures, in ZrO 2–6mol%Y 2O 3 ceramics in both the sintered and annealed states. The compositions of precipitates such as χ L, χ S, χ SS, and small precipitates formed inside χ L, in Cu–11.88Al–5.06Ni–1.63Mn–0.96Ti (wt.%) shape memory alloys have been determined. Under electron beam irradiation, four types of dynamic behavior of the G.P. zones were observed in the Al–6.58Zn–2.33Mg–2.40Cu (wt.%) alloy. The G.P. zone and “G.P. zone-like” defect structures were also distinguished. Lattice distortion profile in the GaAs/In xGa 1-xAs superlattice and two-dimensional lattice distortion around a 60° dislocation core in the InAs xP 1-x/InP superlattice were determined. 相似文献
4.
A thin interphase layer (4 nm) between the merging γ′ precipitates in a chosen model alloy 84.8Ni–12.8Al–2.4Ta was investigated. It is demonstrated that interfacial segregation may occur at an antiphase boundary (APB) interface between the thin layer and one of the merging γ′ precipitates. The magnitude of the lattice displacement (about 1/10[010]) caused by interfacial segregation has been measured both by comparing experimental images with computer simulations, and from high resolution electron microscopy (HREM) fringe spacings using linear regressional analysis. These measurements show a consistent lattice spacing reduction across the APB. Image simulations also highlight the way that the contrast of the bounding partial dislocation affects the APB interface image and can be used to obtain the lattice shift across the interface when the segregation effects on -fringe contrast are significant. 相似文献
5.
Ternary Al–13.8at%Cu–1.6at%Fe alloy was prepared from Al–Cu and Al–Fe alloys at 1000 °C. The ternary Al–Cu–Fe alloy was centrifugally cast to fabricate a new type of functionally graded material (FGM) by a centrifugal in situ method. The structure is expected to differ from that of binary alloys. It was found that the fabricated FGM rings consist of four different phases, namely, Al, Al 2Cu, Al 7Cu 2Fe(ω) and Al 13Fe 4 phases. The shape of ω phase was fiber (needle) judging from the observation by a scanning acoustic microscope (SAM). The position dependence of the microstructure was examined on the fabricated FGM rings, and the volume fraction of ω phase was found to increase toward the outer region of the ring. Moreover, orientation and aspect ratio of the ω phase varied in the rings in a gradually graded manner. Therefore, the present study explores a method to produce fiber-dispersed FGMs by applying a centrifugal in situ method to ternary alloys. 相似文献
6.
The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH 4SO 4 and (NH 4) 3H(SO 4) 2 single crystals were studied. It was shown that the Raman spectra of β-LiNH 4SO 4 passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν3 and ν4 vibrations of the SO 4 tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH 4SO 4 close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO 4 in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH 4) 3H(SO 4) 2 crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (Δ TS 3–5 K) and in Raman spectra studies (Δ TS 12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature TII–III 265 K, at which C2/ c → P2/ n structural phase transition takes place. On the other hand, at TIII–IV 135 K additional domains with W′-type of domain wall orientation were found. 相似文献
7.
The search for dielectric materials with a high dielectric constant and ′ r = ƒ( T) curves with a flat profile fitting the X7R specification is still ongoing. Promising results were obtained by mixing compounds with closely related structures, such as the tetragonal tungsten bronze (TTB) niobate K 2Sr 4Nb 10O 30 and the perovskite Pb(Mg 1/3Nb 2/3)O 3 (PMN). The present study, based on three methods of synthesis, explores the origin of the spreading out of the dielectric curves ′ r = ƒ( T). For the composition 10 x K 0.2Sr 0.4NbO 3 (KSN) + (1 − x)Pb(Mg 1/3Nb 2/3)O 3 (PMN) with x = 0.3–0.6, the three synthesis methods provided similar characteristics and for the highest perovskite ratio ( x = 0.3), the ′ r = ƒ( T) curve exhibits a flat profile. When lithium is used as a sintering agent, ′ r = ƒ( T) curves present a linear dependency with the temperature. These materials are also characterized by a structural and a microstructural inhomogeneity. Two phases TTB and perovskite type, different from KSN and PMN, are present after calcination and sintering, but not evenly distributed. The PbO loss during sintering also contributes to the evolution of the properties of the material. 相似文献
8.
A general method is presented for determining mixed-mode stress intensity factors KI and KII from isochromatic fringes near the crack tip. The method accounts for the effects of the far-field, non-singular stress, σ ox. A non-linear equation is developed which relates the stress field in terms of KI, KII, and σ ox to the co-ordinates, r and θ, defining the location of a point on an isochromatic fringe of order N. Four different approaches for the solution of the non-linear equation are given. These include: a selected line approach in which data analysis is limited to the line θ = π and the K---N relation can be linearized and simplified, the classical approach in which two data points at (rm, θm) are selected where rm/θ = 0; a deterministic method where three arbitrarily located data points are used; and an over-deterministic approach where m (>3) arbitrarily located points are selected from the fringe field. Except for the selected line approach, the method of solution involves an iteractive numerical procedure based on the Newton-Raphson technique. For the over-deterministic approach, the method of least squares was employed to fit the K-N relation to the field data. All four methods provide solutions to 0.1% providing that the input parameters r, θ, and N describing the isochromatic field are exact. Convergence of the iterative methods is rapid (3–5 iterations) and computer costs are nominal. When experimental errors in the measurements of r and θ are taken into consideration, the over-deterministic approach which utilizes the method of least squares has a significant advantage. The method is global in nature and the use of multiple-point data available from the full-field fringe patterns permits a significant improvement in accuracy of KI, KII, and σox determinations. 相似文献
9.
The damping properties of Zn–22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement ( δ) using a low frequency inverted torsion pendulum over the temperature region of 10–230 °C. An internal friction peak was separately observed at about 218 °C in the Zn–Al alloy and at about 195 °C in Zn–Al–Sc–Zr alloy. The shift of the δ peak was found to be directly attributed to the precipitation of Al 3(Sc, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al–Sc–Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al–Sc–Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn–22 wt.% Al alloy. 相似文献
10.
Gamma double prime (γ′′), precipitation was studied in Alloy 718 using isothermal and isochronal aging heat treatments applied between 943 and 1003 K. It is shown, that the coarsening behavior of γ′′ precipitates follows the coarsening kinetic predictions of the Lifshitz–Slyozov–Wagner (LSW) theory. The activation energy for γ′′ growth has been determined as equal to 272 kJ mol −1 and seems to be controlled by volume diffusion of niobium in the matrix. The energy of the γ′′/matrix interface, Γ, has been found to be 95 ± 17 mJ m −2 by assuming that the γ′′ precipitates adopt a disk shape which minimizes the total energy. This energy includes a volume distortion term calculated from the Eshelby inclusion theory and a surface component which is assumed to be isotropic. This interfacial energy is discussed and compared with the energy of γ′/matrix and γ′′/matrix interfaces in other superalloys. The constant K′′ of the LSW law time dependence has been calculated using the value of interfacial energy and the activation energy of γ′′ precipitates coarsening and is found to be in good agreement with our experimental values. 相似文献
11.
Wrought aluminum alloys can be effectively fabricated by a strain-induced, melt-activated (SIMA) process. The SIMA method involves plastic deformation of an alloy to some critical reduction point and a semi-solid heat treatment in the solid–liquid temperature range. The semi-solid heat treatment is a key process to control the semisolid microstructures. In this paper, the microscopic morphology of a cold-deformed SIMA treated Al–4Cu–Mg alloy has been investigated, and the effects of microstructural evolution, precipitation behavior and dislocation morphology on the mechanical properties are discussed. The experimental results show that the number of CuAl 2 ( θ phase) precipitates and the dislocation density of Al–4Cu–Mg alloy decreased gradually by the semi-solid heat treatment. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appeared and evolved to reduce the stored energy. With an increase of the holding time in the semi-solid heat treatment, the ultimate strength and yield strength decreased. The reduction of these mechanical properties of the SIMA treated Al–4Cu–Mg alloy is mainly due to the decrease of refinement strengthening, solution strengthening, and dislocation strengthening in the semi-solid heat treatment. 相似文献
12.
The atomic structure of a common precipitate in the Al–Mg–Si system has been determined. It is isotypic with TiNiSi (space group Pnma) and contains four units of MgAlSi in a unit cell of size a = 0.675 nm, b = 0.405 nm, c = 0.794 nm. EDS analyses support the composition. A model was based on the atomic structure of the β′ precipitate, electron diffraction and high-resolution transmission electron microscopy (HRTEM) images. A quantum mechanical refinement of the model removed discrepancies between simulated and experimental diffraction intensities. Finally, a multi-slice least square refinement confirmed the structure. The structural relation with β″ is investigated. A similar Mg–Si plane also existing in β″ and β′, can explain most coherency relations between the precipitate phases and with matrix. 相似文献
13.
The SiC(OAl) fibers and the SiC(Al) fibers were fabricated by the use of aluminum-containing polycarbosilane (Al–PCS) precursor. The two types of fibers have been characterized. Chemical element analysis, AES, SEM, XRD, RMS and NMR have been employed. The chemical formula of SiC(OAl) fibers is SiC 1.31O 0.25Al 0.018 with C and O rich on the surface. The microstructure of SiC(OAl) fibers is a mixture of β-SiC nanocrystals, free carbon, and an amorphous silicon oxycarbide (Si–C–O phase), which have been confirmed by an amount of SiC 2O 2, SiCO 3, SiO 4 and SiC 3O units in the 29Si MAS NMR spectrum. A small quantity of aluminum is embedded uniformly in the Si–C–O amorphous continuous phase. For SiC(Al) fibers, nearly stoichiometric composition was confirmed as chemical composition of SiC 1.03O 0.013Al 0.024. The fiber is composed of a large number of β-SiC crystallites, a small amount of -SiC crystalline and SiC amorphous phase. The aluminum in the SiC(Al) fibers mainly exists in two manners: Al–C bonds connected with the surfaces of the β-SiC grains and Al–O bonds, or Al 2O 3, to the amorphous phase. 相似文献
14.
A complete set of high-temperature data relevant to rafting, i.e. the elastic constants of the individual γ and γ′ phases and the elevated temperature lattice mismatch between the phases, was generated for two model ternary Ni–Al–Mo single crystal alloys. The directionality of rafting was examined experimentally in the same alloys upon uniaxial loading in compression and tension along a 100 cube axis. The key material properties and corresponding directional coarsening observations are discussed in view of the various models for rafting published in the literature. 相似文献
15.
A systematic study of four ternary TiAl-based alloys with constant Ti content of 52.2at.% and variable Si content ranging from 0.3 to 2.7at.% (Al in balance) was conducted. The alloys were prepared from elemental powders via a route including powder mixing, precompaction, cold extrusion, and reactive hot-isostatic pressing. All investigated alloys contain the intermetallic compounds γ-TiAl, 2-Ti 3Al, and ζ-Ti 5(Si,Al) 3. The microstructure can be described as a duplex structure (i.e., lamella γ/ 2 regions distributed in a γ matrix) containing ζ precipitates. With increasing Si content, the number of primary ζ precipitates increased and the γ grain size became finer while the lamellar volume fraction decreased slightly. 相似文献
16.
Second harmonic generation in novel pyroelectric liquid crystal polymers (PLCP) made from a series binary mixtures, was studied using 1100 nm as the fundamental wavelength. The PLCPs were prepared by photo-polymerization of binary mixtures of two monomers which exhibit a smectic C * phase, A2c (4″-( R)-(−)-2-[(10-acrylo-yloxy)decyl]oxy-3-nitrophenyl 4-{4′-[(11-acryloyloxy)-undecyloxy]phenyl}benzoate) and Alb (4″-(( R)-(+)-2-octyloxy)-3″-nitrophenyl 4-(4′-(11-acryloyloxy)undecyloxy)-phenyl)-benzoate). The highest d16 and d23 coefficients were found to be in the range 0.65–0.8 pm/V, and differed depending on the detailed preparation of the sample. All cases of polymers formed from the chiral smectic C* phase showed an SHG-signal with no external field present, indicating that polar order became fixed. The SHG-signal was found to increase with the tilt angle of the FLC molecules. 相似文献
17.
Spray-formed Al–Fe alloys having undergone high-speed deformation were examined under a high-voltage electron microscope. Two types of specimens were examined; one containing fine Al 13Fe 4 particles, and the other containing large particles. In the former specimen, deformation is found to proceed in three patterns, depending on specimen thickness and strain rate: (1) without deformation of the Al 13Fe 4; (2) breaking of the Al 13Fe 4; or (3) melting of the Al 13Fe 4. Local melting is found to alter some of the Al 13Fe 4 particles, to impart five-fold symmetry in diffraction or an amorphous structure. In the latter specimen, introduction of glide dislocations enabled us to determine a shear system in the mc102 monoclinic c2/ m crystal of Al 13Fe 4. On the bases of these observations, the mechanism of high-speed deformation is discussed while taking into account the highly stressed and/or heated states of Al 13Fe 4 embedded in Al matrix. 相似文献
18.
Stable vacuum deposition of a new europium(III) complex, Eu(DBM) 3(L) {DBM=dibenzoylmethanato, L=3-ethyl-2-(4′-dimethylaminophenyl)imidazo[4,5-f]1,10-phenanthroline}, were verified by ultraviolet–visible and infrared spectroscopy. By using the vacuum deposited film of the Eu(III) complex as the emitting layer, aluminum tris(8-hydroxyquinolinate) (AlQ) as electron-transporting layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as hole-blocking layer, N,N′-diphenyl- N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD) as hole-transporting layer, a four-layer electroluminescent device of (+)indium–tin oxide/TPD(40 nm)/Eu(DBM) 3(L)(40 nm)/BCP(10 nm)/AlQ(40 nm)/Mg:Ag(110 nm)/Ag(60 nm)(−) gave high efficient and pure red light emission with a luminance of 230 cd/m 2. A comparison of the electroluminescence properties of the four-layer device with those of a two-layer and a three-layer device was made. 相似文献
19.
The fatigue crack propagation behavior of Ti–5Al–2.5Fe with various microstructures for biomedical applications was investigated in air and in a simulated body environment, Ringer's solution, in comparison with that of Ti–6Al–4V ELI and that of SUS 316L stainless steel. The crack propagation rate, d a/d N, of Ti–5Al–2.5Fe in the case of each microstructure is greater than that of the Widmanstätten structure in Ti–6Al–4V ELI in air whereas d a/d N of Ti–5Al–2.5Fe is nearly equal to that of the equiaxed structure in Ti–6Al–4V ELI in air when d a/d N is plotted versus the nominal cyclic stress intensity factor range, Δ K. d a/d N of the equiaxed structure and that of the Widmanstätten structure in Ti–5Al–2.5Fe are nearly the same in air when d a/d N is plotted versus Δ K. d a/d N of Ti–5Al–2.5Fe is nearly equal to that of SUS 316L stainless steel in the Paris Law region, whereas d a/d N of Ti–5Al–2.5Fe is greater than that of SUS 316L stainless steel in the threshold region in air, when d a/d N is plotted versus Δ K. d a/d N of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is nearly the same in air and in Ringer's solution when d a/d N is plotted versus the effective cyclic stress intensity factor range, Δ Keff, whereas d a/d N of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is greater in Ringer's solution than in air when d a/d N is plotted versus Δ K. 相似文献
20.
This paper reports the influence of In 2O 3 film structure on gas-sensing characteristics measured in steady state and transient modes. Films were deposited by spray pyrolysis from InCl 3–water solutions. Correlation between gas-sensing parameters and structural parameters such as film thickness (20–400 nm), grain size (10–70 nm), refractive index and film texture ( I(400)/ I(222)) were established. It was shown that grain size and porosity are the parameters of In 2O 3 films that best control gas response to ozone. In the detection of reducing gases, the influence of film structure is less important. Decreases in film thickness, grain size and degree of texture are the best way to decrease time constants of the gas response of In 2O 3-based gas sensors. 相似文献
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