Indentation characteristics of superelastic nickel-titanium wires and a preliminary study of copper-bonded joints between them

摘要

Wires of nickel-titanium have been tensile tested to evaluate their elastic constants, super-elastic characteristics and strength. These data are compared with the response of the same material to (hot stage) indentation testing, using both nano-indentation and micro-indentation equipment, and both a Berkovich and a spherical indenter. Indentation characteristics indicative of super-elastic behaviour are identified. In particular, the observation of enhanced indentation strain recovery when tested above the A_f temperature, compared with tests performed at lower temperature, is recorded here and appears to represent a reliable indicator of super-elastic behaviour. Wires have also been joined together by liquid phase sintering, after a copper electroplating treatment, and by solid state diffusion bonding. Microstructural studies of these joints revealed the expected phases. Preliminary mechanical studies have given an indication that it may be possible to produce strong, highly porous super-elastic material in this way.