Title: Physical metallurgy of the two-way shape memory effect in TiNi alloys

Authors: Peter Filip, Karel Mazanec

Addresses: Institute of Materials Engineering, Technical University of Ostrava, 17 listopadu, KAT. 636, 708 33 Ostrava – Poruba, Czech Republic. ' Institute of Materials Engineering, Technical University of Ostrava, 17 listopadu, KAT. 636, 708 33 Ostrava – Poruba, Czech Republic

Abstract: The two-way shape memory effect in memory alloys is not an inherent characteristic of a material and depends strongly on its structural state. The quantitative parameters (extent of reversible strains, stability, temperature interval and stresses produced during heating and recovery of |hot shape|) crucially depend on the training route performed. The well trained specimens can do work even if the reversible shape memory effect is widely accepted as an unstable one. The transformation temperatures M_s, M_f, A_s, and A_f decrease after training process and cycling under opposing stresses, the T_R temperature increases in well trained specimens. The formation of trained martensite variants is thermodynamically favoured with respect to other crystallographically equivalent variants. This favouring effect is ascribed to the dependence of variant energy on the internal stresses connected with specific alternate bands observed in the high temperature phase which were interpreted as |ghost martensite|.

Keywords: TiNi alloys; two-way shape memory effect; physical metallurgy; shape memory alloys; titanium; nickel; internal stress.

DOI: 10.1504/IJMPT.1996.036315

International Journal of Materials and Product Technology, 1996 Vol.11 No.1/2, pp.9 - 18

Published online: 02 Nov 2010 *

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