ESOMAT 2009, 06012 (2009)
DOI: 10.1051/esomat/200906012

Influence of fatigue on the nanohardness of NiTiCr-wires

M. Frotscher¹, M. L. Young¹, H. Bei², E. P. George^{2, 3}, K. Neuking¹ and G. Eggeler<sup>1

1</sup>  Ruhr-University Bochum, Institute for Materials, Universitätsstr. 150, 44801 Bochum, Germany
²  Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³  Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA

matthias.frotscher@gmx.de

Published online: 1 September 2009

Abstract
Testing parameters, such as rotational speed and bending radius, have a strong influence on the fatigue life of pseudoelastic NiTi shape-memory alloys during bending rotation fatigue (BRF) experiments [M. F. X. Wagner, Int. J. Mat. Res. 97 (2006), p. 1687-1696. and M. Frotscher, et al., Thermomechanical processing, microstructure and bending rotation fatigue of ultra-fine grained NiTiCr-wires, Proceedings of the International Conference for Shape Memory and Superelastic Technologies (SMST 2007), Tsukuba, Japan, ASM International, (2008), p. 149-158.]. Previous studies showed a decrease in the fatigue life for smaller bending radius (i.e. higher equivalent strain) and larger rotational speed. This observation is associated with an increase of dislocation density, the stabilization of stressinduced martensite during cycling, and an increase of the plateau stresses due to self-heating. In the present study, we examine the influence of these fatigue parameters on the nanohardness and shape recovery of pseudoelastic NiTiCr shape-memory alloy wires by nanoindentation. We show that nanoindentation is a suitable method for the characterization of fatigue-related microstructural changes, which affect the mechanical properties.

© Owned by the authors, published by EDP Sciences 2009