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1.
It was shown that the Hall resistivity xy for LuNi 2 B 2 C and YNi 2 B 2 C is negative in the normal and mixed states and has no sign reversal below T c . In the mixed state the scaling relation xy xx (xx is the longitudinal resistivity) was found for both compounds with 2.0. In the normal state a distinct nonlinearity in the xy(H) dependence, accompanied by a large magnetoresistance, was found below 40 K only for LuNi 2 B 2 C. The difference in the behaviour of Lu- and Y-based borocarbides seems to be connected with the difference in the Fermi surfaces of these compounds.  相似文献   

2.
Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L12), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L10 type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L10 martensite is examined.  相似文献   

3.
The effects of Ta addition on the magnetic properties of permalloy thin films have been investigated. The alloy compositions on a weight basis are (Ni81Fe19)1-x Ta x with 0 x 0.105, and the films are sputtered onto a glass substrate at between room temperature and 300 C. The saturation magnetization and anisotropic magnetic field decrease with increasing Ta content. The saturation magnetization is 0.75 T at 5 wt % Ta. The coercivity remains constant at 125 Am-1. The electrical resistivity increases linearly with increasing Ta content, then saturates at approximately 7.5 wt% Ta. The saturation resistivity is approximately 1.00 m. The magnetoresistivity ratio (/) decreases with increasing Ta content, mainly due to increased electrical resistivity (). The magnetostriction changes from negative to positive with increasing Ta content and reaches nearly zero at 2 wt% Ta. The NiFeTa films containing 5–6 wt% Ta have potential for use as the soft-biasing film in magnetoresistive elements.  相似文献   

4.
Experimental data on the lattice parameter, thermoelectric power, and microhardness of PbTeIn crystals and the conversion fromp- to n-type with increasing indium content can be interpreted under the assumption that the indium in PbTeIn has variable valence: 2In2+ In+ + In3+. A crystal-quasi-chemical model is proposed for defect formation in PbTeIn: the incorporation of In+ into octahedral interstices and In3+ into tetrahedral interstices of the close packing of Te atoms, accompanied by In2Te3 precipitation.  相似文献   

5.
Ductile L20-type wires and+L12-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. y, f and p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in y and f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.  相似文献   

6.
Single crystals of the CuAlFe alloy, containing 14.5 wt% Al and 2.2 wt% Fe were subjected toin situ tensile experiment using straining attachment in a 1 MV electron microscope. Loadelongation curves were obtained for three foil plane/tensile direction orientations: (001) [0 1 0], (0 0 1) [1 1 0] and (1 1 0) [¯1 1 2]. Each crystal was subjected to two cycles of pseudoelastic deformation up to maximum 2% strain, showing almost complete shape recovery. Structure observations and electron diffraction pattern indicated that during deformation of samples of (0 0 1) [1 1 0] and (1 1 0) [1 1 2] orientations, formation of 1 martensite was observed and only at later stages narrow needles of 1 nucleate in front of 1. During pseudoelastic deformation in the (0 0 1) [1 0 0] direction, martensite forms as a mixture of narrow plates possessing either 2H or 18R structures. The following crystallographic relationship between the parent phase and both types of martensite was observed: [1 00] 1 [101] 1 and (0 0 1) 1 (0 1 0)1;(0 0 1) 1 (0 1 0) 1 and [1 1 0] 1 [0 0 1] 1. From the character of sidebands reflections presence of 1 0 1 1 0¯1 static displacement waves was inferred.  相似文献   

7.
Cr-substitution in-FeOOH takes place with changes in the unit cell parameters and a marked decrease in crystallinity. The-FeOOH structure is maintained up to 5.0 atomic % with a progressive diminution of crystallite size, as shown by X-ray line broadening analysis and electron microscopy. The dehydroxilation of the Cr-substituted oxyhydroxide to-sesquioxides and the phase transition sesquioxide take place at lower temperatures than in-FeOOH, due to the lower crystallinity.  相似文献   

8.
-SiAION--SiC composites containing up to 12 wt% -SiC were prepared by pressureless sintering. The strength of composites at room temperature remained relatively unchanged, whereas strength at 1200 °C increased for composites. The fracture toughness (K IC) for composites was higher than that for -SiAION ceramics. The maximum value was 5.4 MPa m1/2 for 6 wt% -SiC, and this was an improvement of 15% in comparison with -SiAION ceramics. From SEM observations, an improvement inK IC values was attributed to crack deflections and branching-off of cracks. Intra-granular fractures were frequently observed in -SiAION. From TEM observations, -SiAION crystals were nanocomposites, within which existed the fine crystals in -SiAION crystal. For composite, -SiAION and -SiC crystals were directly in contact. The mismatching zone was observed in -SiC.  相似文献   

9.
The microstructure and phase transformations occurring in-iron-carbonitrides have been studied by means of X-ray and electron diffraction, electron microscopy and Mössbauer spectrometry. Ordering of the interstitial atoms, N or C, results in a hexagonal unit cell for Fe3(C, N) with parametersa=a3 andc=c wherea andc are the lattice parameters of the hexagonal close-packed (h c p) iron unit cell. Stacking faults on (0001) planes and partial dislocations with Burgers vector b=1/31 0 ¯1 0 are observed in quenched-Fe4 (C, N). After quench-aging, the carbonitrides show a structural hardening due to the precipitation of a metastable phase. Slow cooling of-carbonitrides with less than 25 at% interstitials leads to the precipitation of-carbonitride and ferrite in-phase grains which allows the orientation relationships between the-,- and-phases to be defined and a model of the-phase--phase transformation to be proposed.  相似文献   

10.
The dielectric properties of chemically vapour-deposited (CVD) amorphous and crystalline Si3N4 were measured in the temperature range from room temperature to 800° C. The a.c. conductivity ( a.c.) of the amorphous CVD-Si3N4 was found to be less than that of the crystalline CVD-Si3N4 below 500° C, but became greater than that of the crystalline CVD-Si3N4 over 500° C due to the contribution of d.c. conductivity ( d.c.). The measured loss factor () and dielectric constant () of the amorphous CVD-Si3N4 are smaller than those of the crystalline CVD-Si3N4 in all of the temperature and frequency ranges examined. The relationships of n-1, (- ) n-1 and/(- ) = cot (n/2) (were observed for the amorphous and crystalline specimens, where is angular frequency andn is a constant. The values ofn of amorphous and crystalline CVD-Si3N4 were 0.8 to 0.9 and 0.6 to 0.8, respectively. These results may indicate that the a.c. conduction observed for both of the above specimens is caused by hopping carriers. The values of loss tangent (tan) increased with increasing temperature. The relationship of log (tan) T was observed. The value of tan for the amorphous CVD-Si3N4 was smaller than that of the crystalline CVD-Si3N4.  相似文献   

11.
The objective of this paper is to develop the load separation method for evaluating the pl and pl CMOD plastic factors used in the J estimation approach based on load versus displacement records. Appropriate forms for the geometry and deformation functions have been suggested from the EPRI Handbook solutions to produce the separable form for the load. The obtained functions are applied to evaluate the pl and pl CMOD plastic factors for center cracked tension specimen. The present load separation method gave results which are somewhat different from the estimated values of pl given in the literature. For shallow cracks, the pl and CMOD pl plastic factors show considerable variation with crack size and the strain hardening exponent. For a deeply cracked CCT specimen, the CMOD pl factor tends to the pl factor and equals approximately unity. Abbreviations: CCT – center cracked specimen; CMOD – Crack Mouth Opening Displacement; EPRI – Electric Power Research Institute; FEM – Finite Element Method; LLD – Load Line Displacement.  相似文献   

12.
The study of the direct current electrical conductivity, , of freshly prepared -Fe2O3 and that of a sample stored for seven days in static air suggests that -Fe2O3 adsorbs oxygen and water from the atmosphere. From infra-red spectra it is deduced that the absorbed water in -Fe2O3 is present as the physically adsorbed water and as lattice water. The adsorbed oxygen and physically adsorbed water are removed by heating to 100 C, while the lattice water remains in -Fe2O3 even up to 280 C. The removal of lattice water is associated with a decomposition during which some of the hydrogen formed occupies the vacancy sites. This suggested formation of the hydrogen ferrite phase is based on the kink in the log against T –1 curve observed at 177 C. This kink is very well resolved for a sample equilibrated at 100 C in normal atmosphere, and the measurements of above 100 C of this sample are done in an N2 atmosphere. The suggestion that the hydrogen ferrite phase is formed has been substantiated by comparison of the X-ray diffraction patterns of -Fe2O3 heated under the different atmospheres. From the log against T –1 plot for a sample heated under a nitrogen atmosphere the activation energy is small (< 0.05 eV) up to 215 C, and it is comparatively large (0.95 eV) above 215 C. These results suggest a hopping mechanism for the direct current electrical conductivity of -Fe2O3. This suggestion has been substantiated by data of the temperature variation of Seebeck voltage.  相似文献   

13.
Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x and when the (non-dimensional) surface heat flux is –x are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value 0, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >0, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as 0 and as –1, and the natures of these singularities are discussed.  相似文献   

14.
Conversion-electron Mössbauer spectra of epitaxial -Fe16N2 and -Fe8N films have been studied and their differences are discussed in detail. The Mössbauer spectrum of -Fe16N2 can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mössbauer spectrum of -Fe8N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for -Fe16N2 than for -Fe8N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for -Fe16N2. The iron moments tend to locate in the film plane for -Fe16N2 and to arrange perpendicularly to the film plane for -Fe8N.  相似文献   

15.
An investigation was carried out to study the phase transitions in Cu-Ge thin films (80–200 nm in thickness) containing 0, 5, 15, 20, 25, 30, 35, 40, 45 and 50 at% Ge, and the corresponding effects on electrical resistivity. For these films, the phase transitions were found to follow the sequence: -phase (disordered face centred cubic, fcc, solid solution); 5 at% Ge -phase (disordered hexagonal close packed, hcp); 15 at% Ge -phase + 1-phase (ordered orthorhombic, Cu3Ge); 20 at% Ge 1-phase; 25 at% Ge (1-phase + progressively increasing proportions of a disordered Ge-rich solid solution); 30–50 at% Ge. Germanium was found to have no marked effect on grain size of all films studied excluding grain boundaries as electron scattering centres. Transition of the -phase into the -phase was found to occur in a highly coherent manner, which could be related to the reduced stacking fault energy of Cu by the addition of Ge. Most evidence pointed out that the initial increase in resistivity within the -phase range was related to hcp scattering centres, which could be associated with a localized high concentration of Ge. At 15 at% Ge, the resistivity reached a maximum value of about 50 cm associated with the complete transformation of -phase into the -phase. With continued increase in Ge concentration, the resistivity was found to gradually decrease reaching a minimum value of about 10 at 25 at% Ge, which was correlated with complete transition of the -phase into the ordered 1-phase (Cu3Ge). It was shown that the superlattice of Cu3Ge could directly be derived from the disordered -phase by minor atom rearrangement on the [0 0 0 1]hcp plane. Even though, minor proportions of a Ge-rich solid solution containing a small concentration of Cu were formed at Ge concentrations above 25 at%, the minimum resistivity of 10 cm was maintained as the Ge concentration was increased to 35 at%. Subsequently, the resistivity was increased reaching about 46 cm at 50 at% Ge.  相似文献   

16.
A metastable titanium alloy containing 10 wt % Zr and 12 wt % V has been found to undergo a substantial age-hardening reaction at temperatures as low as 20° C. The reaction involves continued growth of athermal-phase particles produced during water quenching from the-phase field. The morphology of the as-quenched is retained, implying the absence of long-range diffusion during ageing: this is consistent with the low value of the activation energy measured (93 kJ kg mol–1). It is suggested that the growth is caused by unpinning of/ interfaces as a result of the short-range motion of interstitials present in the alloy. The age-hardening produces a severe loss in tensile ductility and inhibition of stress-induced martensite formation.  相似文献   

17.
Magnetoconductance and excess conductance due to superconducting fluctuations in aluminum films are measured in order to study the temperature dependence of the pair-breaking parameter at temperatures nearT c . The parameter M is estimated from the relation =/8k B Tin, where in is the inelastic scattering time deduced from the analysis of the magnetoconductance. The parameter F is determined by fitting theories to data on the excess conductance at zero magnetic field. It is shown that: (1) For films with a wide range of the sheet resistanceR , 12R 200 /, the temperature dependence of M nearT c agrees well with the theory of Brenig et al. (2) For clean films withR 100 /, the value of F analyzed with theories including the correction term to the Maki-Thompson contribution shows almost the same temperature dependence as M . In a film withR 200 /, however, a discrepancy between M and F remains.On leave from College of General Education, Kyushu University, Ropponmatsu, Fukuoka, Japan.  相似文献   

18.
The liquid-phase transport phenomena which occur at the surface of iron-base alloys during corrosion have been analysed. These mechanisms determine either the maintenance of bare metal or the precipitation of solid corrosion products, the build-up of a corrosion deposit and the control of its thickness, and finally, the kinetics of the electrochemical reactions under the deposit. Although it is shown that pure precipitation-redissolution or direct formation reactions are impossible, the only conceivable mechanisms are nevertheless closely related, because the transport of iron between the metal and the external corrosive medium occurs chiefly either via the solid phase of the deposit (for soluble deposits), or via the liquid phase permeating its porosities (for insoluble deposits). It is also shown that, depending on the precipitation conditions, any given solid compound Fe n X2 can lead to three types of deposit with quite different properties. (i) Soluble deposits: moderately protective, steady-state corrosion insensitive to potential, but highly sensitive to turbulence; (ii) Insoluble cationic deposits (controlled by the removal of Fe2+ cations by liquid-phase diffusion): highly protective, corrosion rate slightly sensitive to potential, and insensitive to turbulence. (iii) Insoluble anionic deposits (controlled by the diffusional supply of the precipitatable anion X n– : slightly or unprotective, corrosion slight or insensitive to the presence of the deposit; possibly profuse deposit if steady state corrosion is not attained. This theoretical analysis can retrospectively explain numerous experimental observations reported in the literature, such as the incubation time before the drop in corrosion rates, the multiple forms of CO2 and H2S corrosion, the role of Ca2+ ions, erosion-corrosion and bacterial corrosion. This analysis also paves the way for the reliable laboratory prediction of real corrosion rates under deposits.  相似文献   

19.
The electric Ohm resistivity of electroless Cu depositions on dielectric substrates as a function of their thicknesses is studied. Substantial deviations (up to 10–20 times) from the standard resistivity ( = 1.7 cm–1) below 0.5 (m thicknesses are observed. The experimental data show for the entire region of thicknesses (d 0.07–5 m) a power function between the relative resistivity changes (/) and the inverse thickness of depositions (d )–(/ (1/d )0.8. This empirical relation is discussed as an effect of the porous structure of the metallic layers deposited on the substrate. A scanning electron micrography was applied in order to visualize the morphology of the depositions. The micrographs clearly show the evolution of the deposition profile: starting from separate islands at the very beginning of the process, and gradually covering the entire area with continuous but porous metal layers.  相似文献   

20.
Supercarrier effective mass isotope effect (exponent ) is investigated using a two-band model with interband pair scattering. The corresponding repulsive interaction incorporates besides the dominating electronic (Coulomb) part an electron-phonon contribution inversely proportional to the ionic mass factor. Calculations illustrating the behaviour of T c , its isotope exponent , and with doping in La 2–x Sr x CuO 4 type underdoped system reflect the observed tendencies. 2 Both and diminish with doping, the sign of is opposite to . A typical estimation gives || 0.2.  相似文献   

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