The use of time-of-flight neutron diffraction to study grain interaction stresses

Abstract

Time-of-flight neutron diffraction, using the General Purpose Powder Diffractometer at the IPNS (Intense Pulsed Neutron Source) at the Argonne National Laboratory, has been used to measure residual stresses in deformed, polycrystalline Zircaloy-2. It was found that a plastic tensile strain or 3% caused the ( 10 10 ) and ( 11 20 ) prism lines in the diffraction pattern to shift to higher d-spacings, while the (0002) basal line was shifted to a lower inter-planar spacing. Compressive deformation reversed the direction of the shifts, with the prism and basal planes being left in residual compression and tension respectively. The magnitude and sign of the residual stresses, which result from the interaction among the grains in the deforming polycrystalline specimen, are consistent with the texture and anisotropic yield surface of Zircaloy. For the specimen deformed to 424 MPa in tension, the principal residual stresses after unloading were −188 MPa in the 〈 c〉 direction and 173 MPa in the direction normal to the prism planes. The result is in good agreement with an analysis of the problem that considers an idealized texture that is representative of that found in Zircaloy-2 rod. The experiments demonstrate that time-of-flight neutron diffraction can be a sensitive and powerful tool for measuring residual stresses in bulk materials, where conventional X-ray techniques would be inapplicable.