Selected Area Channeling Patterns Research Articles

Crystallographic orientation relationships in coalescing sintered tungsten spheres

Earlier model experiments have shown that specific processes of coalescence occur during the sintering of tungsten particles in liquid nickel. In this work, measurements of crystallographic orientation were made on such coalescing sintered tungsten spheres using “selected area channeling patterns” in a scanning electron microscope. There is evidence that the growing neck in the contact region between two neighbouring spheres has the same crystallographic orientation as the sphere where growth begins. Furthermore, it is suggested that the necks often grow in favored crystallographic directions. Theoretical considerations on crystal growth mechanisms confirm this hypothesis.

The effects of dispersoids upon the micromechanisms of crack propagation in AlMgSi alloys

The effect of dispersoids containing Mn or Cr. in a series of peak-aged AlMgSi alloys, upon the crack-tip plastic zone size has been studied by the use of Selected Area Channelling Patterns (SACPs). In the absence of such dispersoids. the alloy fractures in a brittle intergranular fashion; when the particles are present, the alloys are ductile but still fracture in a predominantly intergranular manner but with an increase in the size of the plastic zone associated with the crack tip. It is suggested that the toughening effect of the dispersoid phase is indirect through its effect upon the matrix grain size and upon the distribution of slip. Fracture occurs because slip bands impinge on grain boundaries, causing a local strain concentration which at some critical value nucleates a void, thereby causing an increment of crack extension.

Grain boundary energy and the rotation and translation of Cu spheres during sintering onto a substrate

A technique for measuring the rotation and lateral movement of small Cu spheres during sintering on to single crystal substrates is described. The rotation of the spheres about each of three perpendicular axes is derived from selected area channelling patterns observed in a scanning electronmicroscope (SEM). The Shewmon sphere rotation mechanism is re-examined and shown to involve a rolling translation. The measured sphere translations are often larger than expected from the rotation and this is ascribed to grain boundary sliding during sintering. Rotation about the axis normal to the boundary is much faster than the Shewmon rotation, confirming the Pond-Smith rotation mechanism. The possibilities of using single sphere rotation trajectories and rotation velocities to evaluate the orientation dependence of grain boundary energy are discussed.

SEM imaging of the cell structure of dislocation networks in cold worked cu single crystals

AbstractIn certain metallurgical applications of SEM, such as the observation of deformation effects, and the recovery and recrystallization processes in bulk specimens, it is of special interest to obtain information about local inhomogeneities of the dislocation densities in a sample. This can be obtained using TEM on thin foils. Previously information on distortion in cold‐worked specimens was obtained by measuring the dependence of the deterioration of the resolution of the selected area channelling patterns (SACP) on the degree of deformation. This method, however, is not applicable to highly deformed materials.Direct SEM imaging of the cell structure of the dislocation network has been achieved without resolving single dislocations by using a suitable arrangement of specimen and detector, such that only backscattered electrons (BSE) leaving the surface at a large angle to the normal contribute to the image signals. The signal‐to‐noise ratio was improved to the degree that it was possible 1) to image the cell structure of the dislocation network and 2) on heating the specimens, to record the growth of recrystallized regions with TV‐frame frequency.The imaging of the cell structure gives qualitative information about the degree of crystal deformation and the crystallographic direction of grain boundary motion during recrystallization.

Analyses of faceted fracture surfaces of fatigue-tested type 304 stainless steel by means of selected area channelling patterns

Analyses of faceted fracture surfaces of fatigue-tested type 304 stainless steel by means of selected area channelling patterns

The study of local plastic strain distribution in aged Al alloys by selected area channelling patterns in the SEM

It is shown that SACPs can be obtained from fully aged At-Mg-Si alloys, and a semiquantitative relationship has been obtained between the quality of the patterns and the percent plastic strain in the material. The technique has been used to compare the distribution of strain adjacent to a propagating crack (a) in a ternary alloy, when the fracture path is intergranular and (b) in an alloy containing Mn, when transgranular fracture takes place. A marked difference in the dimensions of the plastic zone associated with the crack was recorded

The rotation between selected area channelling patterns and micrographs in the SEM

The rotation between selected area channelling patterns and micrographs in the SEM

A Scanning Electron Microscope Study of In1 − xGax P

The SEM has been used to study the crystal perfection and chemical homogeneity of crystals. Secondary electron micrographs were used to study the surface topography and microstructure away from and at inhomogeneities. Chemical and crystallographic data were obtained using the x‐ray wavelength dispersive and energy dispersive analyzers and selected area channeling patterns. The channeling patterns showed that In and Ga can be substituted directly into a common (column III) sublattice without gross distortion of the lattice and without generation of unacceptable levels of structural defects. The crystals were chemically homogeneous (less than 2% maximum) except at or near inclusions.

Scanning electron microscope selected area channelling patterns from 1 micron specimen areas

Scanning electron microscope selected area channelling patterns from 1 micron specimen areas

Scanning electron microscope selected-area channelling patterns: dependence of area on rocking angle and working distance

Scanning electron microscope selected-area channelling patterns: dependence of area on rocking angle and working distance

Selected area channelling patterns in the scanning electron microscope

A technique is presented and illustrated for generating orientation dependent electron channelling patterns in the scanning electron microscope from small selected areas on the surface of bulk specimens. Methods of reducing the pattern area to 1 to 2 μm in diameter are discussed. Numerous applications not previously possible are listed.

Optimum conditions for generating channelling patterns in the scanning electron microscope

The optimum conditions are discussed for generating channelling patterns (i.e. orientation dependent lines and bands of contrast) in the scanning electron microscope. From considerations of the electron optics it is shown that patterns of highest angular resolution may be obtained by establishing a compromise between a small divergence in a collimated beam and a high beam current at the specimen surface. It is also shown that surface detail finer than 50 μm may be resolved and superimposed on channelling patterns with only small loss in pattern resolution. Finally, a technique is presented for obtaining selected area channelling patterns from areas smaller than 100 μm across.