Local composition and microstructure control for multiple pseudoelastic plateau and hybrid self-biasing shape memory alloys

Abstract

Shape memory alloy (SMA) materials with multiple pseudoelastic (PE) plateaus, and hybrid components with both the PE and the shape memory effect (SME) have been designed with a newly developed processing protocol. This protocol utilized a pulsed laser based vaporization process to precisely alter the local composition of NiTi based SMAs. Each laser pulse decreased local Ni composition by 0.16at.%, leading to controlled changes in transformation temperatures. Control of the local composition enabled strengthening by cold work and heat treatment, while maintaining distinct SMA properties throughout the material. The combined cold rolling and annealing used in this study significantly increased the yield strength of the materials allowing for tuneable performance offerings. These included the multiple PE plateau stresses, or combined SME and PE properties in a monolithic tensile specimen. The synergistic behavior of adjacent locally processed regions demonstrated a significant increase in SMA functionality and their potential in future application. These novel technologies are now being applied in a multi-force orthodontic archwire capable of simultaneously applying biomechanically optimized tooth moving forces to each tooth along the dental arch.