Microstructure, martensitic transformation, mechanical and shape memory properties of Ni-Co-Mn-In high-temperature shape memory alloys under different heat treatments

The microstructure, martensitic transformation behavior, mechanical and shape memory properties of Ni40Co10Mn41+xIn9-x, (x=0, 2 and 4) high-temperature shape memory alloys annealed at 900 degrees C for 24 h or at 800 degrees C for 2 h were investigated, respectively. The tetragonal martensite phase and fcc gamma phase are observed in all the studied alloys. The reversible martensitic transformation temperatures of the alloys increase with the increases of the electron concentration and the tetragonality of martensite phase. The amount of gamma phase gradually increases with the decrease of In content, and much more gamma phase in the alloys annealed at 900 degrees C results in slightly larger compressive fracture strain. Although the alloys with x=0 and 2 have a mass of gamma phase, they still exhibit good shape memory properties. The amount of gamma phase reaches about 20% in the alloy with x=0 after annealed at 900 degrees C, but a full recovery strain of 3.6% and a two-way shape memory effect of 0.8% can be obtained after two thermomechanical cycles. (C) 2015 Elsevier B.V. All rights reserved.