April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 6 8 medical components, with a maximum mean strain of 1.2%, and maximum strain amplitudes ranging from 0.72 to 1.64%. Compared with the austenitic parent material, the R-phase material tolerated 0.1–0.3%higher strain amplitudes (Fig. 2). VARIABILITY OF TWIN BOUNDARY VELOCITIES IN 10M Ni–Mn–Ga MEASURED UNDER µ s-SCALE FORCE PULSES A. Mizrahi, D. Shilo, and E. Faran Twin boundary motion is the basic mechanism responsi- ble for fast actuation of magnetic shapememory (MSM) alloys. Previous studies implied on a wide diversity of twin boundary velocities measured under similar conditions. Here, a data set of more than 400 velocity values is measured under con- ditions that are relevant for MSM applications and represents the dynamic behavior of 73 twin boundaries. Ve- locities are measured using an electro-mechani- cal setup that applies a controllable μs-scale force pulse and combines force measurements with high-speed imaging. The latter allows extracting velocities of individual twin boundaries, which are then correlated to the macroscopic stress in the sample. The appearance of type I twins is more prevalent than type II, resulting amuch larger data set for type I twins. Statistical analysis of velocity points of type I twins reveals an increasing trend of the velocitywith themacroscopic stress, as well as useful information on the probability distri- bution of velocity data. Velocities of type II twins exhibit large variability over a relatively narrow stress range. This can reason the large differences in maximal velocities reported previously for this twin type. The obtained statistical data can im- prove the design and modeling of MSM actuators (Fig. 3). LARGE NON-ERGODIC MAGNETOELASTIC DAMPING IN Ni–Mn–Ga AUSTENITE L. Bodnárová, P. Sedlák, O. Heczko, and H. Seiner Resonant ultrasound spectroscopy was used to analyze magnetoelastic damping in Ni–Mn–Ga single crystals in aus- tenite and premartensite phases. Crystals with different treat- ment were studied, exhibiting different density of antiphase boundaries (APBs), as confirmed by magnetic force micros- copy, and different magnetic behavior. For a quenched single crystal with high density of APBs, extremely strong damping was observed in a broad temperature range in the austenite phase. It was shown that this damping is history-dependent, i.e., non-ergodic, appearing only during heating runs preceded by a premartensite→austenite transition. We suggest that this non-ergodicity results from the pinning of the fine magnetic domain structure on APBs and other defects (Fig. 4). Fig. 2 — Fatigue testing results for AMA (left) and RMR (right) processes, in the form of a strain limit diagram. Fig. 4 — Magnetization curves of annealed (red) and quenched samples (black). Fig. 3 — Velocity data points (total of 414 points) acquired from 73 twin boundaries during a series of consecutive force pulse tests. Data points for type I and type II twin boundaries are shown in red and blue markings, respectively. 1 4 SMJ HIGHLIGHTS