Temperature Memory Effect Of Stress Annealing-Induced Anisotropy In Metallic Glasses

Stress annealing (SA)-induced magnetic anisotropy is known in iron, nickel, and cobalt-based ferromagnetic metallic glass ribbons and it has already been used in commercial processes. Uniaxial elastic strain is introduced by SA and is quenched into the ribbons even after cooling and removing the external stress. The release of the uniaxial quenched strains is clearly observed as an anomaly in the linear thermal-expansion coefficient (LTEC) when the ribbon is reheated without stress. The rate of strain release corresponding to the LTEC anomaly reaches a maximum at the temperature at which the original SA was performed. We have observed this temperature memory effect over the whole temperature range from 280 to 400 degrees C, which is below the crystallization temperature T-x. The observed results are explained well by the existence of a localized "flow unit" embedded in an elastic matrix, which is accepted as the origin of the shear band formation and rejuvenation of metallic glasses with T-g (glass transition temperature) T-x), the results here indicate that the same important structural feature is common to metallic glasses with both T-g < T-x and T-g > T-x. Because magnetization behavior is very sensitive to the existence of residual elastic strain which is difficult to evaluate in most of the metallic glasses, detailed studies and a revival of interest in ferromagnetic ribbons will help us to understand more about the nature of the localized flow unit, as well as nonaffine deformations.