The application of neutron diffraction to materials science problems in the Canadian nuclear industry

Diffraction is one of the principal tools of the scientist for studying materials. The broadening of the diffraction lines provides information on the degree of cold-work and their intensity gives the degree of crystallographic alignment or texture generated in the manufacturing process. The main advantage of neutron diffraction over X-ray diffraction is that thermal neutrons easily pass through, for example, 25 mm of steel, so that measurements can be made at depth in engineering components. A program at Chalk River to investigate the industrial applications of neutron diffraction began with measurements on over-rolled Zr-2.5Nb pressure tubes, a topic of major concern in the eighties. It was quickly realized that neutrons could provide measurements of residual stress accurate enough to be of real interest. Over the ensuing period, major contributions have been made in measuring stresses and crystallographic texture in components for the nuclear industry including end-fittings, steam generator tubing, pressure tubes and calandria tubes, and weldments. In addition to work for the nuclear industry, there have been many applications in the aerospace, automotive, defence and pipeline industries in Canada and throughout the world. Residual stresses arise because of inhomogeneous plastic deformation of the material. Inhomogeneous plastic deformation not only occurs on a macroscopic scale but also on the scale of the grain size. The stresses that occur on this scale are called intergranular or type-II stresses. These intergranular effects, taken with the strong crystallographic alignment in zirconium alloy tubing, determine the growth of components in the reactor environment. Systematic studies of the origin of intergranular residual stresses arising from thermal effects and plasticity effects were carried out on Zircaloy-2 and Zr-2.5Nb alloys which have led to a theoretical understanding of component growth. Finally, a very recent texture scanning technique was able to shed light on the microstructure of zirconium alloy components. (authors) 17 refs. 14 figs