On the generation of microstrains during the plastic deformation of Waspaloy

Abstract

Neutron diffraction has been used to characterize the development of microstrains during the plastic deformation of the polycrystalline nickel-base alloy, Waspaloy. Two types of experiment were performed: (i) in situ tensile testing on the diffractometer to determine the response parallel and perpendicular to the loading direction and (ii) measurement of the orientation dependence of the microstrain accumulation using a Eulerian cradle. Large residual microstrains are shown to develop. Along the loading direction, these are typically tensile in the γ′ phase and compressive in the γ phase; however, the values are sensitive to both the orientation of the diffracting crystallite and the amount of plastic deformation of the material. The behaviour is due to the differential deformation between grains in differing orientations (intergranular microstresses) and the two phases (interphase microstresses). It is shown that at low bulk plastic strains, intergranular microstresses develop rapidly, whilst at larger plastic strains the microstresses arising from interphase interactions become dominant. These effects have implications for the determination of residual stresses using diffraction-based techniques and these are discussed.