[P1-13] Anelastic recovery of a steel wire under pure shear strain with various magnetic treatments
Elastic property of a metal under pure shear strain is quite different from that under other strain, since the former doesn’t have the volume change of the specimen. Without the volume change, elasticity under the pure shear strain is mainly caused from bowing-out deformation of dislocations in slip planes. After external force is removed, the solid will immediately return to its original size. It indicates deformed dislocation lines are straitened instantly in this condition. On the other hand, people has observed slow recovery of the size of the specimen after unloading, which is called anelasticity. When anelastic phenomenon occurs under pure shear strain, it indicates some dislocations slowly recover its bowing-out shape because of the existence of weak pinning sites. Since dislocations are known to interact with magnetic domain walls in ferrous materials, the domain walls can partially act for weak pinning sites for anelasticity.
To prove this mechanism, we will observe anelastic recovering of steel compression coil spring, whose strain is mainly pure shear state, under various magnetic treatments. The residual elongation cannot be explained from simple relaxation phenomenon of macroscopic spring dynamics. Since the amount of anelastic recover is influenced with magnetic treatment during compression condition, magnetic domain walls can work as weak pinning sites for some dislocations. As temporal change of elongation is logarithmically changed, resultant number of bowing-out dislocations is inversely proportionally decreased with time during recovering.
At last, we will discuss the mechanism of interaction between dislocation and magnetic domain wall. In iron, easy-magnetization axes are <100> and 180-degree magnetic domain walls are located along {011} plane. Slip planes of bcc iron are {110} plane, and dislocation lines are perpendicular to {110}. Since [01-1] dislocation line, which is perpendicular to a magnetic domain wall, has no interactions to the wall, most dislocation lines across the 180-degree wall in this manner. We will discuss the origin of weak pinning sites of dislocation from the distribution of Bloch wall and Bloch line in the domain wall. And we will show the possibility to understand the interaction from magnetic force caused by swirling flow of electron along dislocation line.
To prove this mechanism, we will observe anelastic recovering of steel compression coil spring, whose strain is mainly pure shear state, under various magnetic treatments. The residual elongation cannot be explained from simple relaxation phenomenon of macroscopic spring dynamics. Since the amount of anelastic recover is influenced with magnetic treatment during compression condition, magnetic domain walls can work as weak pinning sites for some dislocations. As temporal change of elongation is logarithmically changed, resultant number of bowing-out dislocations is inversely proportionally decreased with time during recovering.
At last, we will discuss the mechanism of interaction between dislocation and magnetic domain wall. In iron, easy-magnetization axes are <100> and 180-degree magnetic domain walls are located along {011} plane. Slip planes of bcc iron are {110} plane, and dislocation lines are perpendicular to {110}. Since [01-1] dislocation line, which is perpendicular to a magnetic domain wall, has no interactions to the wall, most dislocation lines across the 180-degree wall in this manner. We will discuss the origin of weak pinning sites of dislocation from the distribution of Bloch wall and Bloch line in the domain wall. And we will show the possibility to understand the interaction from magnetic force caused by swirling flow of electron along dislocation line.