Effect of coherent nanoprecipitates on martensitic transformation in Tb-doped NiMnGa melt-spun ribbons

Abstract

Martensitic transformation (MT) behavior is compactly related with multiple effects in shape memory alloys. Here we report a special effect of broadening the MT temperature span with keeping the hysteresis stable via introducing coherent nanoprecipitates. The MT temperature span stabilize in the single-phase region and significantly expands with the formation of coherent nanoprecipitates in the matrix. This effect disappears after the growing up of precipitates during annealing treatment. Microstructural analysis indicates a heterogeneous distortion in matrix lattices with the largest distortion up to 10% in the matrix induced by the perfect coherent relationship between matrix and nanoprecipitates. A qualitative thermodynamic model based on Landau theory is employed to understand the effect on heterogeneous local stress field leads on MT temperature span. This work may promote the understanding of MT behavior in ferromagnetic shape memory alloys.