Residual lattice strains in plastically deformed poly-crystalline metal aggregates

Abstract

The residual lattice strain observed by X-ray diffraction methods in plastically extended polycrystalline aggregates has been investigated. It is shown that, if several diffraction lines are examined, the residual lattice strains vary both in magnitude and in sign. It is known that one of the causes of internal stresses in a plastically deformed polycrystalline aggregate is the variation with orientation of the yield tensions of the crystals in the aggregate. Since only grains with certain orientations contribute to a given diffraction line, the lattice strain measured is not the mean strain in all the crystals, which should be zero, but the average of the strains in those crystals with particular orientations, which may be positive or negative. It is considered that this constitutes one of the reasons for the hitherto unexplained observations which have been made on residual lattice strains. Quantitative conclusions from this explanation are in satisfactory agreement with observations.