Damping property and its mechanism of iron-based shape memory alloy

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Pseudoelasticity, internal friction and low cycle fatigue property have been systematically investigated on Fe-Mn-Si shape memory alloys (FMS) and on Fe-Mn high damping alloys (BFM). The FMS exhibit two kinds of pseudoelasticity: (1) transformation pseudoelasticity which appears between As and M_d temperatures, (2) pseudoelasticity which appears even below A_s (anelasticity). The latter is caused by motion of thermally activated partial dislocations. Internal friction measurements have revealed that the FMS show strain amplitude dependent damping behavior. Damping properties measured by means of low cycle fatigue tests at strains more than 10^<-4> are accompanied by reversible motion of γ/e interfaces. All of these phenomena are related to static or dynamic motion of partial dislocations. Fine dispersion of NbC carbide particles in FMS refines e martensite plates, because the NbC particles act as nucleation sites for the martensite. This microstructural modification is effective for im … More proving functional properties associated with static motion of γ/e interfaces, i.e., the shape memory properties and transformation pseudoelasticity of the alloys. However, it interrupts the functional properties associated with dynamic motion of the interfaces, such as damping properties and internal friction. The damping properties at larger strains more than 10-3 (plastic deformation region) are lower in the BFM than in the FMS, because slip deformation surpass the stress-induced martensitic transformation in the BFM. On the other hand, the internal friction values of the BFM are equivalent to or higher than those of the FMS, because of high stacking fault probability. Magnetic transition of the FMS with various Si and Mn concentrations, strength of the austenite matrix, stacking fault energy and the volume of e martensite have also been summarized and the necessary condition for obtaining good anti-seismic damping properties are concluded as follows: (1) Ms and TN temperatures be below room temperature, (2) low stacking fault energy (<20mJ/m^2) and (3) high strength of the austenite (>300MPa). Less