摘要:

The single‐crystal elastic moduli,C11,C12, andC44of three fcc cobalt‐iron alloys (Co&sngbnd;6 at.% Fe, Co&sngbnd;8 at.% Fe, Co&sngbnd;10 at.% Fe) were measured in the range 0–315°C. In additionC11for the Co&sngbnd;6 at.% Fe alloy, andC′=(1/2)(C11+C12+2C44) for the three alloys are measured over the temperature range 0–1250°C. Plots of the elastic moduli vs temperature exhibit a change in slope and deviation from linearity in the neighborhood of the Curie temperature. The temperature variation of the shear anisotropy in the fcc phaseAfcc(≡2C44/C11−C12) differs among the three alloys.Afccexhibits a highly positive temperature dependence in the Co&sngbnd;10 at.% Fe alloy and a slight negative dependence in the Co&sngbnd;6 at.% Fe and Co&sngbnd;8 at.% Fe alloys. Previous statements in the literature that the hcp&rlarr2;fcc transformation in cobalt is preceded by a highly negative temperature dependence of the shear anisotropy ratioA(≡C44/C66) in the hcp phase between 523°K and the transition at about 743°K is not borne out by the present results. Rather it appears that the hcp&rlarr2;fcc transformation involves a change fromA>1 in the hcp phase toA<1 in the fcc phase.

ISSN:0021-8979    

DOI:10.1063/1.1662508

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The full‐wave solution to the problem of acoustic surface‐wave scattering on a homogeneous isotropic three‐quarter space of Poisson's ratio &sgr;=0.245 has been obtained by a finite‐difference iterative method. The amplitude coefficients for Rayleigh wave transmission and reflection at the 270° corner were found to be 0.28±0.02 and 0.09±0.01, respectively, while the corresponding phase shifts were 140±10° and −125±10°. All of these results, which are independent of wavelength, agree well with previously published experimental and theoretical work. About 90% of the incident energy is lost to body waves and the scattered energy‐density pattern indicates that over half of this energy sweeps past the corner and propagates into the body of the medium in the form of bulk modes. Some of the incident energy tends to follow the free surface by swinging around the corner while the reflected wave appears to be launched mainly by the action of a virtual source located at the corner which is excited by the incoming wave and radiates into the three‐quarter space. The accuracy of the finite‐difference technique has also been verified by comparing the iterated results for Rayleigh wave propagation on a homogeneous isotropic semi‐infinite half‐space with the analytically exact results. This basic method may be extended to solve problems involving layered geometries.

ISSN:0021-8979    

DOI:10.1063/1.1662509

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A statistical method for calculating the effects of dislocation movements is described; the method is based on a realistic model although the effects of cross slip are not included. The long‐range interactions between dislocations are considered to be limited by large intrinsic stresses and image stresses. The numerical results indicate that with sufficient time, about half of the dislocations are annihilated while the other half are bound in dipoles. The maximum strain is found to be almost independent of either the initial dislocation density or the initial dipole density. The calculated maximum strains are in fair agreement with the experimental data published by other investigators.

ISSN:0021-8979    

DOI:10.1063/1.1662510

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The precipitation behavior of evaporated Al/Si films with up to 1.8% Si is studied by microscopy as well as by resistance measurements after isochronal and isothermal aging. After deposition of the film most of the Si is precipitated. Temperature treatments above 300°C cause the solution of Si into Al. Aging of a supersaturated solution results in precipitation on grain boundaries at a rate that is much greater than in bulk Al/Si. The precipitation is described as a two‐dimensional diffusion‐limited process. A theoretical expression for the rate constant permits the determination of the diffusion coefficient of Si in Al. This is much greater than in bulk Al/Si and has an activation energy of about 0.85 eV. In view of the small vacancy concentration in the film, these results are explained by diffusion along dislocations, in agreement with electron micrographs revealing a dislocation density of about 1010cm−2.

ISSN:0021-8979    

DOI:10.1063/1.1662511

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A quasianalytic solution for the atomic displacements of a discrete two‐dimensional lattice containing a crack is obtained. We assume that the force laws are linear up to a critical displacement when the bond snaps, which is the basic assumption of the lattice static approximation. When compared to the classic Griffith continuum description, new results are: (i) a predicted and observable lattice trapping of the crack, (ii) difficulties with the interpretations of the crystal surface energy in a cleavage experiment, and (iii) a predicted characteristic crack creep phenomenon under external constant stress. The present theory shows how two separate ``surface energies'' are inferred from the stress to open and to close a crack, and on our model these energies differ from one another by a large factor of 5.7. The thermodynamic ``surface energy'' is not related to either of these quantities. Experimental verification of the lattice trapping of cracks is thought to be most readily and directly obtained by observations of the creep of a crack under high vacuum conditions.

ISSN:0021-8979    

DOI:10.1063/1.1662512

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The pyroelectric behavior of as‐received 2‐mil polyvinylidene fluoride films was studied as a function of the poling treatment. It is shown that poling induces a thermally reversible electric polarization in addition to an electric polarization which vanishes upon the first heating of the sample. Experimental evidence is given that the reversible polarization involves charge injection from the electrodes in addition to a field‐induced structural change (probably the formation of oriented crystalline form I). For short poling times ([inverted lazy s] seconds) the mechanism of charge injection appears to be dominant. Initial results of the temperature and voltage dependence of the dc conductivity and of the temperature dependence of the dielectric loss at 50 and 100 Hz for unpoled and poled 2‐mil polyvinylidene fluoride (PVF2) films are presented.

ISSN:0021-8979    

DOI:10.1063/1.1662513

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Refractive index, birefringence, and linear electro‐optic (EO) effect of BO6‐type oxides have been analyzed using a two‐term Sellmeier dispersion relation. Two oscillators correspond to two main transitions; the transition tod&egr; conduction band with a transition energy of 4–6 eV and that to thed&ggr; band with an energy of 9–11 eV. It is found that the contribution of the latterd&ggr; transition to the refractive index in the visible to the infrared region is larger than that of the former, and that the dispersion energyEidispfor thed&ggr; transition is approximately equal to that for the average single oscillator. The birefringence and the linear EO effect are explainable by the polarization‐induced changes in the position and the strength of thed&egr; transition. In the ferroelectric phase, the change in the oscillator position is found to be proportional to the square of the spontaneous polarizationPs2. On the other hand, the change in the oscillator strength consists of the terms proportional toPs2andPs4. The second term leads directly to two observed features: the quadratic EO coefficient depends onPs; and a slight difference exists between the coefficients derived from the spontaneous birefringence and the linear EO effect.

ISSN:0021-8979    

DOI:10.1063/1.1662514

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A perturbation theory for the electric potential associated with a Rayleigh wave propagating on a layered surface is presented. The case analyzed is that of a thin piezoelectric film on a nonpiezoelectric substrate. The film is regarded as perturbing the Rayleigh wave of the substrate. The velocity, stress, and electric potential within the film are approximated by power series, and the coefficients of the series are found from Poisson's equation and the mechanical equations of motion in terms of the particle displacements of the unperturbed Rayleigh wave of the substrate. The results obtained using unperturbed Rayleigh wave displacements are shown to be in good agreement with exact calculations in the thin‐film limit (kh≤0.2), while the use of exact particle displacements and phase velocity are shown to yield excellent agreement out tokh≤0.9. Generalities regarding the properties of the two media that control the coupling of thin‐film overlay acoustic surface‐wave transducers are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1662515

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The torsional stress‐strain curves for single‐crystal copper samples were determined at hydrostatic pressures from 1 bar to 15 kbar. The pressure derivative of the yield stress was found to be 3.8×10−3. At strains of about six, the pressure derivative of the flow stress increased to 1.78×10−2. Stress‐strain curves for the various pressures are provided. A simple model of dislocation cell structure is presented in an attempt to explain the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.1662516

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Equations and graphs are developed for rapid estimation of sputtering rates at the first wall of controlled thermonuclear reactors (CTR). High‐energy particle sputtering yield data and potential particle fluxes are presently not readily available for most materials and many reactor designs, thus the equations were set up to provide rapid estimation of sputtering effects when data become available. Limiting wall sputtering‐yield‐particle‐flux products were determined according to the equation &Sgr;S&mgr;&phgr;&mgr;<Kd(t′)/t′, whereS&mgr;and &phgr;&mgr;are the sputtering yield (atoms/particle) and flux (particles/cm2sec) of bombarding species &mgr;,d(t′)is the allowable wall thickness removal (in cm) int′ years, andKis a material constant.Kvaried little (from 1.36×1015to 3.28×1015) for the wall materials considered (V, Mo, Nb, Ta, Zr, stainless steel, and Al2O3), so that a conservative estimate for the limiting sputtering‐yield‐particle‐flux product is 1015times the allowable sputtering rate in cm/yr. The sputtering yield in molecules per particle given for compounds such as Al2O3must be multiplied by the number of atoms in the molecule to satisfy this relationship. Use of the equations to estimate wall sputtering of pulsed (high‐&bgr;) and steady‐state (low‐&bgr;) reactors indicated that sputtering rates will be sufficiently high that they cannot be ignored. Factors reducing sputtering erosion rates, such as surface roughness, impurity effects, and sputtered material redeposition, are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662517

出版商:AIP    

年代:1973

数据来源: AIP