Boundary Inclination Research Articles

Mixed convection from a heated inclined plate in a channel with application to CVD

A numerical study based on governing equations in skewed coordinates is made to determine the influence of forced convection on natural convection from an inclined, heated plate situated inside a horizontal channel. The forced convection is found to augment the heat transfer as well as to make the heat transfer rate more uniform on the upward-facing side of the plate. The boundary conditions, inclination angles and offset positions are found to have significant effects on the interaction of forced and natural convection.

Electromigration in Thin Films of Au on GaAs

AbstractEvolution of the fractional change of electrical resistance ΔR/R in thin films of Au on (001) substrates of semi-insulating GaAs has been investigated as a function of time t, temperature T, and current density j. Initially, ΔR/R increases linearly with increasing t for constant T and j, and exponentially with increasing T for constant t and j, characterized by an activation energy of 0.73 eV. An analytical model is developed to evaluate ΔR/R for the early stages of electromigration. This model is based on flux divergence at grain boundary triple junctions resulting from variations of grain boundary inclination and/or diffusivity. Using a Monte Carlo method, conducting lines containing a prescribed number of random triple junctions are simulated, wherein distribution of mass flux divergence determines initial values of ΔR/R. Moreover, by selection of an appropriate failure criterion, the sequence of cumulative failures is characterized by a log-normal-like distribution, which defines mean time to failure and corresponding standard deviation. In general, the model is in good agreement with experimental observations.

Oblique grain boundaries: Analysis of light and electron beam induced current profiles in silicon

Asymmetrical light and electron beam induced current profiles have been previously attributed to a difference of the diffusion length on the two sides of the grain boundary. We show that this feature is instead due to the grain boundary not being perpendicular to the surface. In this geometry, the equations describing the minority-carrier diffusion are not solvable by analytical procedures. A method for their numerical solution is hereby introduced, fast enough to allow the use of minimization procedures. A good agreement has been found between fitted values of the grain boundary inclination and those directly measured.

Investigation of Grain Boundary Migration in Situ by Synchrotron X-Ray Topography

AbstractGrain boundary migration has been investigated in prestrained monocrystalline specimens of aluminum in situ, continuously and at temperatures ranging from 415 to 610°C by synchrotron (polychromatic) x-ray topography (SXRT). In general, new (recrystallized) grains nucleate at prepositioned surface indentations and expand into the prestrained matrix, revealing complex evolution of crystallographic facets and occasional generation of (screw) dislocations in the wake of the moving boundaries. Analysis of corresponding migration rates for several faceted grain boundaries yields activation energies ranging from 56 to 125 kCal/mole, depending on grain boundary character. it is concluded that grain boundary mobility is a sensitive function of grain boundary inclination, resulting in ultimate survival of low-mobility (faceted) inclinations as a natural consequence of growth selection. Advantages and disadvantages associated with measurement of grain boundary migration by SXRT are enumerated and corresponding results are interpreted in terms of fundamental relationships between grain boundary structure and corresponding migration kinetics.

A lock-in model for the atomic structure of interphase boundaries between metals and ionic crystals

The low energy interphase boundaries between noble metals (Au, Cu) and various ionic crystals (LiF, KCl, NaCl, MgO, A1 2O 3, mica) were determined at 550°C by means of the boundary energy induced rotation of small (~ 1 μm) spheres. The systems were chosen so that the effect of lattice mismatch (varied between 1.3 and 35.1%), the effect of lattice structure (cubic/cubic and hexagonal/cubic) and chemical effects could be studied. The results obtained suggest that boundary models based on the coincidence concept are not applicable to interphase boundaries between noble metals and ionic crystals because the low energy boundaries observed were not of the coincidence type and existing coincidence orientation relationships did not result in low energy boundaries. However, the atomic structure of the low energy interphase boundaries observed may be understood in terms of the following “lock-in model”. A low energy interphase boundary results if the close packed rows of atoms at the “surface” of the metal crystal fit into the “valleys” between close packed rows of atoms at the “surface” of the ionic crystal. This model seems to predict correctly the experimentally observed correlations between the interfacial energy and the boundary inclination, the lattice mismatch and the lattice structure of the two phases involved.

On the relation between creep cavitation and grain boundary orientation

1. 1. The influence of grain boundary inclination on the creep cavity nucleation rate and the cavity growth rate has been studied using SEM and a stereo microscopy technique in a CuSb alloy. 2. 2. Both the cavity growth rate and the cavity nucleation rate were found to be higher on transvers boundaries. 3. 3. A possible explanation for the higher nucleation rate on boundaries by stochastic grain boundary sliding has been proposed.

Mixed mode stress intensity distributions for part circular surface flaws

Using the frozen stress method, mixed mode stress intensity factor (SIF) distributions were obtained for a series of low aspect ratio part circular surface flaws in flat plates over a depth to plate thickness range of 0.20–0.70. Mode I results were compared with Mode I solutions in order to sense the influence of the crack surface inclination to the free boundary. It was found that maximum SIF values did not necessarily occur at maximum flaw depth. A rationale is offered to explain this observation. It was also found that the effect of the boundary inclination was to reverse the relative magnitudes of K 1 K ̄ 1 and K 2 K ̄ 2 in going from a 30° to a 60° crack surface inclination with the boundary.

The Effects of Interfacial Torque on the Geometry of Twin-Grain Boundary Intersections

The characterization of a grain boundary in a thin film section by transmission electron microscopy has been described previously. In addition, the geometrical configurations resulting from interfacial torque at twin-grain boundary intersections have been described by the use of the electron microscope. There have been, however, no attempts to systematically study the effect of interfacial torque on the geometry of twin-grain boundary intersections in thin metal films. Neither have there been any attempts to systematically study the interrelationships of the degrees of freedom characterizing a grain boundary in a three-dimensional thin section in the electron microscope. The present work describes the relationship of grain boundary misorientation, inclination (θ), and asymmetry (Φ) to relative interfacial free energy; and the dependence of these parameters on relative interfacial torque at twin-grain boundary intersections observed by transmission electron microscopy.

The effect of inclination on grain boundary energies

The energy of high angle [001] and [110] tilt boundaries was measured as a function of the boundary inclination by observing the equilibrium angle between two high angle boundaries and a small angle tilt boundary. The measurements suggest that the fit of the atoms in the boundary (boundary coincidence) is crucial for the energy of a high angle grain boundary.

Investigation of grain boundary energetics in Er2O3 thin foils by transmission electron microscopy

AbstractThe oxidation of erbium thin films directly within the electron microscope, and the subsequent grain growth and equilibration of the Er2O3 foils have allowed the true dihedral angles at grain boundary triple junctions to be calculated. It is observed that a mean dihedral angle of 120° obtains for these oxide‐ceramic films; and the comparison of the three‐dimensionally computed dihedral angles with the two‐dimensional angles measured directly from electron microscope images of grain boundary triple junctions in Er2O3 exhibited a uniqueness which questions the necessity of three‐dimensional corrections for this particular property. The distribution of relative grain boundary free energy ratios in Er2O3 foils is also calculated; and the spread of this data is interpreted to represent the effects of the relative grain orientations composing a triple junction. The mean boundary inclination is observed to be 71.1°, which suggests an influence on grain boundary equilibration in thin foils of surface image forces. The results generally indicate that the application of techniques previously utilized in the study of metallic grain boundary energetics is equally valid in certain oxide‐ceramic thin films.