On the origin of the two-stage behavior of the martensitic transformation of Ti50Ni25Cu25 shape memory melt-spun ribbons

The observation of two successive stages in the martensitic transformation of Ti50Ni25Cu25 shape memory melt-spun ribbons after long-term annealing was formerly reported (H. Rosner, A.V. Shelyakov, A.M. Glezer, It. Felt, P. Schlossmacher, Mater. Sci. Eng. A273-275 (1999) 733). Microstructural investigations revealed the formation of thin plate-like precipitates. It was concluded that the two-stage transformation behavior is governed by the precipitation of these thin plates. Recent experiments are presented which now show that a change of transformation behavior call occur in the course of isothermal heat treatments owing to a crystalline surface layer in the as-spun state of melt-spun ribbons. The previous interpretation of the two-stage transformation behavior considering the influence of plate-like precipitates is corrected in this communication. (C) 2001 Elsevier Science B.V. All rights reserved.