Thermal and damping behaviour of magnetic shape memory alloy composites

Single crystals of ferromagnetic shape memory alloys (MSMA) exhibit magnetic field and stress induced strains via energy dissipating twinning. Embedding single crystalline MSMA particles into a polymer matrix could thus produce composites with enhanced energy dissipation, suitable for damping applications. Composites of ferromagnetic, martensitic or austenitic Ni–Mn–Ga powders embedded in a standard epoxy matrix were produced by casting. The martensitic powder composites showed a crystal structure dependent damping behaviour that was more dissipative than that of austenitic powder or Cu–Ni reference powder composites and than that of the pure matrix. The loss ratio also increased with increasing strain amplitude and decreasing frequency, respectively. Furthermore, Ni–Mn–Ga powder composites exhibited an increased damping behaviour at the martensite/austenite transformation temperature of the Ni–Mn–Ga particles in addition to that at the glass transition temperature of the epoxy matrix, creating possible synergetic effects. (paper)