Abstract

In this chapter, we describe the influence of ion implantation on the microstructural modifications in TiNi SMA thin films. We focus on investigations involving 5 MeV Ni ion irradiation since it can be used as a means to selectively alter the transformation characteristics and to develop NiTi based thin film actuator material for MEMS devices. The primary effects of ion implantation on microstructure are summarized.

Introduction

This chapter discusses the influence of high energy particle irradiation on the shape memory properties of shape memory alloy (SMA) thin films. In general, SMAs, like TiNi, are very sensitive to high energy particle irradiation and undergo structural changes that can suppress martensitic transformations and thus their shape memory properties. The simplified explanation for this sensitivity to particle irradiation is that the martensitic transformation relies on the local atomic order of the crystal. The introduction of defects by high energy particle irradiation, such as in ion implantation, can destroy the local structural and chemical order that suppresses the SMA's ability to undergo a martensitic transformation and the related shape memory properties. It is these detrimental effects that limit the use of SMA in harsh environments, like space, where the defect production from cosmic radiation can render SMA actuators inactive.

The negative effects of particle irradiation on shape memory properties can, in fact, be useful. If the high energy particle material interactions are well understood, they can be used to tailor the shape memory response and engineer monolithic SMA actuators.