X-ray diffraction study of stacking faults and twins in iron alloys and cementite Fe3C

A simple geometrical method of the analysis of X-ray diffraction patterns from crystals with arbitrary atomic lattice containing stacking faults and thin microtwin plates is presented. The theory takes account of the effect of changing interplanar spacing along the line of the intersection of a lattice plane with a stacking fault or a microtwin. This approach significantly simplifies the analysis of diffraction effects and their summation when considering polycrystalline objects. A detailed study of the size of microtwins and true blocks of martensite crystals in Fe-Ni alloys containing from 10 to 33 % Ni is presented. It was found out that microtwin thickness obtained from the diffractional analysis coincided with that determined by the transmission electron microscopy. A model of stacking fault in the (001) plane of cementite is proposed. Diffraction theory was considered and concentration of stacking faults was determined based on anisotropy of diffraction maxima broadening. The theory presented in the paper can be used both for the analysis of experimental diffraction patterns and for further development of diffractional methods of studying the structure of metals and alloys.