Small-Angle Scattering of X-Rays and Neutrons from Deformed Metals

Abstract

X-rays or thermal neutrons may be scattered at small angles from deformed metals due both to ``true'' small-angle scattering and to double Bragg reflections. These two effects are discussed theoretically and compared to see how one may be distinguished from the other in the results of experimental observations. Experiments are described on the small-angle scattering of x-rays from polycrystalline copper and single grains of aluminum deformed by cold-work or fatigued in pulsating tension. The results show in a direct and conclusive way that almost all of the scattering is due to double Bragg reflections. No surface scattering has been observed. Double Bragg reflections have been eliminated in experiments on the small-angle scattering of cold neutrons from cold-worked and fatigued copper and aluminum. The results, which indicate the magnitude of the ``true'' scattering, are consistent with scattering from dislocations. Hence there is no direct evidence of the existence of cavities in cold-worked or fatigued metals as the result of small-angle scattering experiments with either x-rays or neutrons.