Role of Residual Stresses as Determined by X-Ray Diffractometry on Magnetic Properties of 4-79 Molybdenum Permalloys

Abstract

AbstractResidual stresses in several batches of heat-treated 4-79 molybdenum Permalloy finished laminations were measured by X-ray diffraction technique. This involved determination of macrostresses from line shift of (331) reflection by the two-exposure diffractometric technique as well as the determination of microstresses from half breadth of the same line profile. It was observed that the residual stresses In all batches of laminations were small and the variations in residual stresses from one batch of laminations to another were not appreciable, considering the scatter in laminations within each individual batch. Simultaneous magnetic measurements showed considerable variation in magnetic properties from batch to batch; e.g., a five-fold variation in normalized hysteresis loop and a two-fold variation in the magnetic “softness” parameter. On subjecting individual batches of laminations to various thermal and thermomagnetic treatments below 650 C, considerable change in magnetic properties was achieved without significantly changing residual stresses. The variation in magnetic properties in finished laminations was ascribed to the difference in effective crystal anisotropy and uniaxial anisotropy caused by variations in thermal and thermomagnetic annealing treatments. The study showed that the variation was not due to any major variation in stress induced magnetostrietive anisotropy.