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 111 direction were prepared by containerless inductive zone melting under Ar atmosphere. The internal friction was measured between temperatures of 300 to1200 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 σ 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 1000 K, indicating a hardening due to precipitates of the σ phase.

Mechanism of void formation in grain interior of ODS alloys

“…Two peaks known as P1 and P2 (at about 520 and 770 • C, respectively) for convenience can easily be distinguished because they appear at different temperature. The references [12][13][14], which reported the results of researching on high-purity Fe-Cr single crystal, indicate that only one peak corresponding to the P1 peak could be observed. The peak was originated from Zener relaxation, in which the activation energy is E = 2.95 ± 0.3 eV and the average pre-exponential factor τ 0 = 3 × 10 −18±1 s. According to Arrhenius relation τ = τ 0 exp(E/kT), the mean activation energy and the mean pre-exponential factor τ 0 of the P1 peak of the ODS single crystal can be calculated.…”