Plastic deformation in structural materials, investigated in situ by neutrons and positrons.

During residual stress measurements by neutron diffraction additional information becomes available through the accompanying high-energy prompt capture gamma radiation, which in turn produces positrons within the bulk of the specimen. Plastic deformation will increase the dislocation density within the material. This leads to an increase in the mosaic spread of the diffraction reflections and to changes of the lineshape of the positron annihilation radiation. The correlation between the width of the Bragg reflections and the S-parameter, which describes the shape variation of the annihilation line was investigated as a function of the degree of plastic deformation. The experimental work was performed at the FRG-I research reactor of GKSS.