Face-centered Cubic Metals Research Articles

超高真空中加熱処理による金属薄膜の粒成長と平坦化

The effect of thermal annealing under ultra-high vacuum on the metallurgical microstructure of (111) -textured face-centered cubic (FCC) metal thin films was investigated. The surface morphology of 500-A-thick metal films drastically changes with increasing annealing temperature. Regardless of the kind of metal, the morphological changes can be classified into four stages, when the annealing temperature, TIR, is normalized by the respective melting point of the metals, TM. In stage I , 0.15 ≤ TIR/TM < 0.3, the surface roughness, Ra, of metal films decreases to ∼ 3 A. In stage II, 0.3 ≤ TIR/TM ≤ 0.35, remarkable grain growth occurs, and the lateral grain diameter exceeds 1000 A. Small (∼ 200 A) crystals appear on the large grains in the stage II’, 0.35 < TIR/TM ≤ 0.45, and they grow large and coarsen the Ra in stage III, 0.45 < TIR/TM. We conclude that ultra-high vacuum annealing in stage II is effective in realizing large lateral grain size with small surface roughness in FCC metal films.

Mechanical properties and interrelationships of poly(methyl methacrylate) following hydration over saturated salts

Three types of specimens were machined from a model unfilled linear poly(methyl methacrylate) (PMMA), which was nominally 1.5mm thick. After pre-condition annealing and pre-drying, the specimens were equilibrated at one of eight relative humidities (RH) at 22 or 37°C. Thereafter, the parallelepipeds were deflected in 3-point bending, the dumbbells were pulled in tension or deformed using a Knoop (HK) microhardness indenter, and the disks were deformed using a Vickers (HV) microhardness indenter. As the RH increased from 0 to 100%, the samples exponentially sorbed 2% w/w of water. Elastic moduli in bending and tension (EB and ET), ultimate tensile strength (UTS), and hardnesses (HV and HK) were inversely and linearly dependent on water uptake (p<0.001). Strain at UTS (εUTS) was independent of weight change; whereas, strain at fracture (εF) was directly and linearly dependent on water uptake (p<0.02). Under these equilibrium conditions of sorption, no evidence was found that sustained the concept that a break in mechanical properties occurred at about 1% sorption as a result of plasticization leading to clustering. After logarithmic transformations of selected mechanical properties, linear correlations were found between HV versus EB (p<0.02) and strength (UTS or YS) versus HV (p<0.001). The results paralleled the relationship found for pure face-centered-cubic (FCC) metals in the former case and was coincident with the relationship for FCC metals in the latter. These interrelationships suggest that the effects of plastic anisotropy are absent in hydrated PMMA and that water continues to facilitate long-range elastic interactions.

INVESTIGATION OF THE ACTIVATION-PARAMETERS OF LOW-TEMPERATURE SLIP IN CUBIC METALS

The macroscopic critical resolved shear stress (CRSS)τ of 9 body-centred cubic (BCC) and 5 face-centred cubic (FCC) metals has been found to vary with temperatureT in the range 0 to 300 K as given by: lnτ=A − BT, whereA andB are positive constants. Theτ−T data have been analysed within the framework of a kink-pair nucleation (KPN) model of plastic flow in crystals. The microscopic parameters of the unit activation process of yielding, e.g. the initial length of the glide dislocation segment, the critical height of the kink-pair nucleated in it, the activation volume associated with the CRSS, and the binding energy per interatomic spacing along the glide dislocation in the slip plane etc., have been evaluated. A consistent picture of the dislocation kinetics involved in the yielding of BCC and FCC metals emerges, which is adequately described by the KNP model of plastic flow in crystals.

The interstitial electron model for metals-a critical appraisal

The interstitial electron model (IEM) of Li and Goddard (1989, 1993) has reproduced with good success the phonon dispersion curves of many face-centred cubic (FCC) metals. The key feature of the model is the location of light interstitial particles in the tetrahedral holes of the structure. In this paper the validity of the model is further tested: (i) by applying it to three additional FCC metals, beta -Co, La and Th; (ii) by using it to calculate anharmonic properties; (iii) by considering extensions to hexagonal close-packed (HCP) and body-centred cubic (BCC) metals. These demanding tests reveal several shortcomings. There is good agreement for the experimental dispersion curves of beta -Co and La, but only if additional interactions and input data are used in the fitting; the agreement for Th is only fair. Applied to anharmonic properties of FCC metals, the IEM cannot explain simultaneously both the temperature dependence of the Gruneisen function and the pressure dependence of the second-order elastic stiffnesses. Other than for Mg and alpha -Co, it cannot reproduce the frequency dispersion curves of HCP metals. Its use for BCC systems is impractical due to the large number of parameters required. Even where the model is successful in predicting dispersion curves, equally satisfactory agreement can be obtained with a valence force-field, sometimes with fewer adjustable parameters.

Crystallography-based prediction of plastic anisotropy of polycrystalline materials

The on-line prediction of metal sheet formability requires that both material characterization (texture identification) and yield loci predetermination be done in very shor time intervals. Of two applicable approaches, i.e., continuum mechanics and crystallography-based methods, only the latter are suitable for this purpose. Several models of plasticity of a polycrystalline material were reviewed, and their applicability to the prediction of plastic anisotropy of face-centered cubic (FCC) metals was evaluated. A tailored set of cold-rolled copper alloy samples was designed and manufactured, representing the wide spectrum of textures and cold work levels typical for the sheet metal industry. The texture was quantitatively described in the form of the orientation distribution functions derived by the inversion of four incomplete pole figures. The Taylor-Bishop-Hill model was applied in order to calculate the planar variation of the plastic strain ratio. The continuum mechanics of textured polycrystals approach was also used for the prediction of the plastic strain-rate ratio for the same set of deformed materials. The theoretical predictions were compared with the plastic strain ratios measured in tensile tests using strain gauges. The applicability of the models for prediction of the plastic anisotropy of FCC metals was discussed in view of the operating deformation mechanisms and other factors such as strain hardening sensitivity and grain size/shape effects.

Mechanical properties of silver at low temperatures

In this study the authors obtained detailed information about the stress, strain, strain rate, and temperature-dependence of plastic flow in cold-worked high-purity (99.99 wt%) silver. They performed tensile and creep tests at temperatures from 77 K to 473 K and at strain rates of 10/sup -8/ to 10/sup -3/ per second. It is generally agreed that silver, like most facecentered-cubic metals, deforms at low temperatures by the dislocation intersection mechanism. The rate-controlling process in the intersection mechanism is the overcoming of obstacles (forest dislocations) by glide dislocations. The process involves the formation of jogs and constrictions, with an activation energy appropriate to those processes. The amount of local deformation per successful event is expressed by an activation volume, or activation area times the Burgers vector. As the density of the forest increases--at higher strains and lower temperatures--the activation area is expected to decrease. At temperatures near half the absolute melting point (617 K) the metal begins to deform predominantly by climb-controlled dislocation creep. The data generated thus far show some interesting phenomena concerning the transition between these two mechanisms.

Theory of muon spin relaxation due to the hopping motion of positive muons in ferromagnets

Abstract The interaction of the magnetic moments of spin-polarized positive muons with the magnetic fields at the interstices in ferromagnetic (or ferrimagnetic) materials may be used to study the localization and the hopping motion of thermalized muons by observing the relaxation of the longitudinal or transverse spin polarization or the shift of the muon spin precession frequency as a function of the orientation of a strong applied magnetic field. The general theory is developed and applied to the special cases of muon diffusion between two types of interstice of tetragonal symmetry in body-centred-cubic metals (α-Fe) or of cubic symmetry in facecentred-cubic metals (Ni). It is shown that by a suitable choice of the strength and the crystallographic direction of the applied magnetic field, quite detailed information on the quantum diffusion of positively charged light particles in crystals may be obtained.

Solute segregation in metals under irradiation

A kinetic model has been designed to study substitutional solute segregation during irradiation in facecentered-cubic metals. The model includes a 100&gt; split interstitial binding to impurities to second-neighbor distances, vacancy binding to impurities to first-neighbor distances, and the possibility of migration of the bound complexes. Also taken into account are the effects of vacancy and interstitial diffusional encounters with impurities and spatially independent reaction terms. The resultant rate equations have been solved numerically for a thin-foil geometry as a function of time for different temperatures, defect-production rates, internal sink concentrations, foil thicknesses, defect-impurity binding energies, and initial impurity concentrations. Using parameters appropriate for Zn in Ag, significant solute segregation is found in the temperature range from $0.2{T}_{m}$ to $0.6{T}_{m}$ (${T}_{m}$ is the melting point). The temperature for maximum segregation is appreciably higher for heavy-ion bombardment or high-voltage-electron-microscope irradiation rates than for fast-reactor irradiation. The present calculations are intended to indicate the general pattern of segregation behavior and would be useful in areas of high-voltage electron microscopy, void formation, radiation-enhanced diffusion, and advanced materials development for nuclear-reactor applications.

Possible magnetic effects due to fine particle metal and intergrown phases in lunar samples

Electron microscopy has confirmed the existence of both body centered cubic (BBC)-α metal and face centered cubic (FCC)-γ metal in lunar fines and breccia samples. Under appropriate conditions of composition, size, and other constraints iron-nickel alloys can exist as FCC phases over the entire range from 0 to 100% nickel. Lunar rock magnetism research has not generally considered the implications of structures, mechanisms, crystallography, and possible interaction effects in fine particle metal. FCC metal is antiferromagnetic (≲ 30 wt % nickel) and would be measured in the paramagnetic component, showing a cryogenic temperature Neel point; only BCC metal would figure in the estimation of the free iron content based on saturation magnetization measurements. Evidence is presented for changes in saturation magnetization, magnetic remanence, and coercivity, and for the introduction of magnetic anisotropy when FCC metal transforms to BCC metal. From the results in the published metallurgical literature it is inferred that the induced magnetic anisotropy observed during plastic deformation of fine FCC iron precipitates in a copper matrix is associated with uniaxial development of BCC plates in the FCC precipitate. Directional impulse or any uniaxial deformation may produce magnetic anisotropy if FCC metal is made to transform to BCC metal (theγ→α M transformation), and there will be an angular dependence for remanence acquisition, because of shape, which must be considered in paleointensity determinations. It should be noted that the transformation can be activated at any temperature below the Curie point of the BCC metal High field rotational hysteresis (Wr) has been measured in lunar fines and rocks, indicating that exchange anisotropy and/or ferromagnetic minerals with large uniaxial anisotropy exist in the lunar samples. The following are possible sources of the hysteresis:

On the Relationship of Texture Changes of Cold-Rolled Face Centered-Cubic Metals During Recrystallization

An analysis of the relationship between the deformation and recrystallization textures in face-centered-cubic metals is presented. The analysis assumes that orientations of the secondary as well as the primary textures are related to the deformation texture. The effect of alloying elements on the recrystallization texture of copper-base alloys is also discussed.