Optimisation of processing and properties of medical grade Nitinol wire

Abstract

The purpose of this paper is to review the current processing and resultant properties of standard Nitinol wire for guide-wire applications. Optimised Ti-50.8at%Ni wire was manufactured according to industry standards by precise control of the composition, cold work and continuous strain-age annealing. Mechanical properties of this wire are reported from -100°C to 200°C to demonstrate the effects of test temperature. Within the ‘superelastic window’ the plateau stresses are linearly related to test temperature. Additional ageing treatments can be used as a tool to fine-tune transformation temperatures and mechanical properties. A review of the fatigue properties of thermomechanically-treated Nitinol wire shows that they are affected by test temperature, stress and strain.

Key Words:

• Nitinol
• shape-memory
• superelasticity
• mechanical properties
• ageing
• fatigue