Abstract
This paper is devoted to the fatigue crack propagation behavior of the pseudoelastic TiNi thin strips in air and corrosive environments of simulated body fluids. The objective of this study was to understand the effect of environment on cyclic crack-growth resistance in a 50.6Ni-49.4Ti (at.%) alloy applied for manufacturing of smart medical microdevices. The goal is to provide the necessary data for the life prediction of micro-implant devices employing pseudoelasticity at human body temperature. Characterization of crack growth rates was performed at 37 °C on middle tension (MT) samples in different environments including air, physiological solution (0.9 % NaCl in water), and aerated Hank's solution. Results indicated that the considerable part of recoverable strain was maintained during cyclic loading. The martensitic phase was always detected at the crack tip. Despite the nucleation and growth of martensitic phase on the crack tip during cycling at maximum stress being well below the yield point, TiNi thin strips were found to have a relatively low fatigue crack growth resistance. This behavior contrasts with behavior of bulk TiNi materials reported previously. No significant differences between other metallic materials typically used in medical applications and investigated TiNi alloys were detected.

Key words
TiNi shape memory alloys, corrosion fatigue, phase transformation, biomaterials

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