Composition dependence of the Zener relaxation in high-purity FeCr single crystals

Abstract

High-purity FeCr single crystals with Cr contents between 34 at% and 60 at% and orientations close to the direction were prepared by containerless inductive zone melting under Ar atmosphere. The internal friction was measured between temperatures of 300 to 1200 K using an inverted torsion pendulum in the frequency range between 2 and 80 Hz. A strong damping is observed below the Curie temperature due to domain wall motion. Above the ferromagnetic transition temperature a relaxation maximum occurs at about 950 K. This relaxation can be assigned to the so-called Zener relaxation which is due to the stress-induced reorientation of short-range ordered Fe and Cr atoms, respectively. An analysis yielded an effective activation enthalpy of (3.1 ± 0.3) eV showing no significant dependence on the composition. The relaxation strength shows a maximum value near the equiatomic composition and decreases for lower and higher Cr contents. Furthermore, the influence of the a phase on the internal friction and the dynamic torsional shear modulus was studied on a single crystal with a Cr content of 48 at%. After annealing for 24 h at 973 K the torsional shear modulus increases with temperature up to over 1000K, indicating a hardening due to precipitates of the a phase.