FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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APPLICATIONS OF NEUTRON DIFFRACTION TO ENGINEERING PROBLEMS
T.M. Holdan, G. Veiling, S.U. MacEwan, J. Wlne.gai and B.M. Pouie.ZZ
Atomic. Ena-igy o () Canada Limited
Chalk Rl\mK, Ontaulo
R.A. Holt
Physical Me.taZlu.igy Rziaafich Laboiatonle.!,
Ottauia, Ontailo
ABSTRACT
Neutron diffraction may be applied with advantage to the study of engineering
problems in areas currently served by X-ray diffraction. At Chalk River, neutron
diffraction has been applied to the measurement of lattice strains in an
over rolled Zr 2.5 wt% Nb pressure tube and in a bent Incoloy-800 steam generator
tube. Basically, the interplanar lattice spacing, deduced from the diffraction
peak, acts as an internal strain gauge. Our experiments on the pressure
tube showed that a major contribution to the lattice strain comes from
grain to grain interactions and allowed us to measure the strain tensor associated
with the overrolling procedure. The experiments on the generator tubing
showed that, even in a cubic material, the strain in the longitudinal direction
is higher by a factor of two for grains aligned with an [002] crystallographic
axis longitudinal than for grains aligned with a [111] axis longitudinal. The
differences originate in the elastic anisotropy of Incoloy-800. A number of
other potential applications of neutron diffraction are discussed.
1. INTRODUCTION
Neutron diffraction can be applied to the study of engineering problems in many
areas currently served by X-ray techniques. The advantages of neutron
diffraction over X-ray diffraction originate in the low neutron absorption and
scattering cross sections of most elements. For example a 1 Â thermal neutron
beam is only attenuated by a factor of 3, 1.3 and 1.1 by a 1 cm thickness
respectively of steel, zirconium and aluminum. Hence one is usually able to
measure peaks diffracted by atomic planes whose normals lie along any chosen
direction in the component. With this flexibility one can examine, for
example, the hoop strain in a tube by passing the beam through one wall and
scattering off the second wall oriented so that the tangent to the tube bisects
the incident and scattered beams. With a thin-walled tube, the property (be it
texture, or strain) is averaged through the wall with neutrons whereas X-rays
measure the property in the first few microns from the surface. With a carefully
collimated beam of neutrons one can, by moving the component through the
point of intersection of the incident and scattered beam, map out the properties
through the bulk [1].