Near-equiatomic Ni-Ti alloys are known to exhibit shape memory effect associated with a B2↔B19’ martensitic transformation. These alloys are often used in various cyclic modes in application, typically as actuators and sensors. The B2↔B19’ martensitic transformation in Ni-Ti is accompanied with a large lattice distortion. Cycling through this transformation, induced thermally, mechanically or by the combination of the two, is found to cause structural damage to the alloys, hence changes their functional properties. This study investigates the effect of transformation cycling and heat treatment on the property stability of near-equiatomic Ti-Ni. It was found that in the case of thermally induced transformation cycling, incomplete transformation cycles caused less structural damage to the matrix than full transformation cycles whereas in the case of mechanically induced transformation cycling via pseudoelasticity in tension, partial or full transformation cycling caused similar property changes. The indifference of the case of pseudoelastic cycling is attributed to the localisation of the deformation, commonly known as the Lüders-type deformation.
|Journal||Key Engineering Materials|
|Publication status||Published - 2006|