SIMULATION OF ELECTRON-DIFFRACTION PATTERNS OF ALLOYS WITH ORIENTED PRECIPITATES

A computer program has been developed to simulate the complicated elec tron diffraction patterns of alloys consisting of an underlying matrix phase in which are embedded various crystallographically oriented pre cipitates. These precipitates consist of different variants each with a specific orientation relationship to the underlying matrix. The prog ram is designed to calculate the number of possible variants and the s pecific orientation of each variant using a general orientation relati onship input by the user, usually in the form of an axis-angle pair or two parallel directions or planes. The program then plots the superim posed diffraction pattern of the matrix and all variants for a given z one axis of the matrix using the calculated orientation relationships of the variants. The crystal symmetries of the matrix and the precipit ate phases are employed for the former, the Ewald-sphere concept for t he latter. The program is also equipped with the option of displaying the indices and relative intensities of the screen-displayed diffracti on spots. Necessary symmetry, atomic scattering and structural data re quired for the computations are incorporated into the program in the f orm of data files. The program developed has been tested for various c ommon orientation relationships, e.g. b.c.c. and fc.c. twins, Bain, Ku rdjumov-Sachs and omega, and some of the simulation results, in the fo rm of variant transformation matrices and diffraction patterns, are pr esented.