Publication V I . Aaltio , Y . Ge , X . W . Liu , O . Söderberg and S - P . Hannula . Effect of magnetomechanical cycling on 10 M Ni - Mn - Ga magnetic shape

Martensitic Ni-Mn-Ga alloys with the five layered modulated structure (10M) provide a way to produce motion by the magnetic shape memory (MSM) effect. MSM actuation is based on alternating the twin structure by applying a magnetic field and/or mechanical stress at suitable ranges. For the actuator use, it is necessary to understand the long-term cyclic magneto-mechanical loading behavior of the actuator material. To evaluate the long-term behavior of the materials martensitic 10M Ni-Mn-Ga single crystal samples were studied in the magneto-mechanical longterm cycling tests under constant pre-stress, using a specifically designed laboratory test platform. A decrease in the magnetic-field-induced strain was observed as the number of cycles accumulated. Crack formation followed the extensive cycling. Growth of the cracks on the specimen surface due to cycling was monitored and the microstructure was studied at certain cycling intervals. The final structure of the cycled specimen was observed by XRD and SEM to detect the possible fatigue induced changes in the microstructure.