Nanocrystalline NiTi Shape Memory Thin Wires for Micro Actuators
Market penetration was driven by superelastic alloys in the medical field, but NiTi alloys are becoming a mature technology also for industrial applications. One of the most promising sectors is that of miniaturized actuators for consumer electronics, especially mobile phone platforms, where tiny wires, in the range of 25 µm in diameter, are used to produce small and high quality actuators for camera modules. SMAs allow a simple material integration by implementing actuation features in standard structures without adding weight, parts and complexity. Upon miniaturization, intrinsic disadvantages of these materials loose significance.
In this work a comprehensive characterization of NiTi shape memory wires with diameter below 50 µm is presented. Special equipment and procedures ad-hoc developed to perform reliable measurements on such tiny wires are described along with their main issues. Considerations about the effects of their nanocrystalline microstructure, as well as enhanced microcleanliness on the functional and fatigue behavior are spent and discussed. An overview of SMA components and actuators under development and future opportunities will also be given.