Time-of-Flight Neutron Powder Diffraction

Abstract

Intergranular or type-2 stresses are stresses on the length scale of the grains which arise from the anisotropy of plastic, elastic and thermal deformation in different crystallite orientations or in different phases in the material. In general the strain measured in a diffraction experiment will be a superposition of macroscopic and intergranular strains so it is important to be able to identify the two contributions. The experimental methods for measuring the intergranular strains with high accuracy are discussed in detail. Three case studies of major interest in materials science are examined. Intergranular strains are generated between the phases present in composite materials because of differences in thermal expansion and different plastic and elastic response to applied loads. Intergranular strains are generated in zirconium alloys through the anisotropy of the coefficients of thermal expansion as the alloy cools from the fabrication temperature and by the anisotropy of plastic deformation. Finally, intergranular strains develop in nickel-based cubic alloys from plastic and elastic anisotropy when these are plastically deformed.