Multiscale twin hierarchy in NiMnGa shape memory alloys with Fe and Cu

Abstract

X-ray microdiffraction and scanning electron microscopy studies reveal 10M martensitic structure with a highly correlated multiscale twin hierarchy organization in NiMnGaFeCu shape memory alloys. High compatibility is found at the twin interfaces resulting in a highly correlated twinned lattice orientation across several laminate levels. The lattice unit cell is described as monoclinic I-centered with a=4.28Å, b=4.27Å, c=5.40Å, γ=78.5°. The modulation is found parallel to the b axis. Thin tapered needle-like lamellae and branching are observed near the twin boundaries.