Long-Term Cyclic Loading of 10M Ni-Mn-Ga Alloys

Abstract

Martensitic 10M Ni-Mn-Ga single crystals are usually applied in the magnetomechanical actuators. Their behavior in the long-term cycling and the factors influencing upon are thus important to know. There are several publications concerning this. However, consistent statistical data is still missing to large extent. In this report we review and analyze the data available in the literature. In conclusion it can be stated that 10M Ni-Mn-Ga single crystals survive well in long-term actuation (millions of cycles) when the frequency of twin variant reorientation is not exceeding 250 Hz, and the strain used in actuation is below 3 %. There are several factors influencing the long-term behavior and these are discussed in more details in this work.

Magnetomechanical properties of a high-temperature Ni–Mn–Ga magnetic shape memory actuator material

“…In recent years considerable improvements have been achieved in the mechanical stability, work output and production of these materials [11][12][13]. Furthermore, actuators, sensors and power generators have been designed based on MSM materials [14,15].…”

Review of MSM Actuators: Applications, Challenges, and Potential

“…The same publication reports that transition of the MSM element into singlevariant state reduces the fatigue life, i.e., full elongation or contraction of the MSM crystal should be avoided and, the operational range of an actuator should hence be limited. Additionally, deformation of a crystal into a single state requires more stress and energy than deformation of a crystal with two or more variant states [22], [25]. Temperature change under cyclic load is shown in [63] to be insignificant: for the MSMA under study, the temperature increased by less than 2 K under load with 300 Hz frequency.…”

“…Longer fatigue life can be achieved by the use of high-quality single crystals and by avoidance of surface wear of the MSMA [23]. Important factors that can help to optimize fatigue performance are listed in [22]. The same work describes defects and other issues with MSMAs that could decrease fatigue life and increase twinning stress in crystals.…”

“…For mm-sized MSMAs, the actuation frequency can reach kHz range [20], and μm-sized MSMAs may have a working frequency of 100 kHz [21]. The material properties of MSMAs are overviewed in detail by I. Aaltio and other authors [22]- [25].…”

Fracture Toughness Evaluation of a Ni2MnGa Alloy Through Micro Indentation Under Magneto-Mechanical Loading

“…loading with magnetic field applied normal to the length of the sample and with a compressive axial stress applied along the length of the sample (normal to the field direction), material samples may developed cracks as illustrated in Figure 3.b. Fatigue studies that investigated either the effect of magnetic or mechanical loading on material's performance have been reported in [4,5,8] and provided valuable insight on the long term behavior of the material. However, there are still a few questions left unanswered, particularly regarding the effect of combined magneto-mechanical loading on the long term behavior of the material.…”