A New Type of X‐Ray and Electron Diffuse Scattering and Corresponding Strain Contrast on Electron Microscopic Images

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Abstract
A kinematic theory is developed for electron elastic diffuse scattering by static distortions, caused by coherent particles in the new phase. It is suggested that the lattice of the new phase differs from the matrix lattice in an arbitrary way. The theory is valid in cases when the matrix and the particles are elastically anisotropic and possess equal moduli. The values of the elastic displacements determining the diffuse scattering are obtained from anisotropic elasticity theory. The isodiffuse surface cross‐sections of the reciprocal lattice planes are calculated for the anisotropic ageing alloy CuBe and the isotropic alloy TaO. These alloys show the precipitation of tetragonal and rhombic phases respectively. The isodiffuse surface sections are in good agreement with the structure of the reciprocal lattice points, obtained on the diffraction patterns; the scattering in these cases also differs considerably from Huang scattering which arises when particles are dilatation centres. A kinematic theory is also developed for the strain contrast caused by the distortions in a solution due to the new phase particles. When the particles are not only centres of dilatation but also centres of an arbitrary deformation, the strain contrast differs from Ashby contrast to the same extent as the diffuse scattering differs from Huang scattering. A comparison is made between the contrast calculated theoretically and that obtained on the micrographs of the alloy TaO.

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