Epitaxial Versus Polycrystalline Shape Memory Cu-Al-Ni Thin Films

Doga Bilican,Pau Solsona,Zoe H Barber,Jordi Sort,Eva Pellicer,Yi Zhu,Jordina Fornell,Alan Lindsay Greer,Samer Kurdi

doi:10.3390/coatings9050308

Abstract

In this work, two different approaches were followed to obtain Cu-Al-Ni thin films with shape memory potential. On the one hand, Cu-Ni/Al multilayers were grown by magnetron sputtering at room temperature. To promote diffusion and martensitic/austenitic phase transformation, the multilayers were subjected to subsequent heat treatment at 800 °C and quenched in iced water. On the other hand, Cu, Al, and Ni were co-sputtered onto heated MgO (001) substrates held at 700 °C. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy analyses were carried out to study the resulting microstructures. In the former method, with the aim of tuning the thin film’s composition, and, consequently, the martensitic transformation temperature, the sputtering time and applied power were adjusted. Accordingly, martensitic Cu-14Al-4Ni (wt.%) and Cu-13Al-5Ni (wt.%) thin films and austenitic Cu-12Al-7Ni (wt.%) thin films were obtained. In the latter, in situ heating during film growth led to austenitic Cu-12Al-7Ni (wt.%) thin films with a (200) textured growth as a result of the epitaxial relationship MgO(001)[100]/Cu-Al-Ni(001)[110]. Resistance versus temperature measurements were carried out to investigate the shape memory behavior of the austenitic Cu-12Al-7Ni (wt.%) thin films produced from the two approaches. While no signs of martensitic transformation were detected in the quenched multilayered thin films, a trend that might be indicative of thermal hysteresis was encountered for the epitaxially grown thin films. In the present work, the differences in the crystallographic structure and the shape memory behavior of the Cu-Al-Ni thin films obtained by the two different preparation approaches are discussed.

Highlights

Shape memory alloys (SMA) exhibit displacive and reversible deformation behavior due to sensing thermodynamic and mechanical changes in their environment [1,2,3,4,5,6,7]
The XRD pattern of the thin film co-sputtered at a high temperature on MgO mainly consisted of textured β austenite, but the Cu9 Al4 phase was present (Figure 2d)
Previous studies on Cu-Al-Ni bulk shape memory alloys have reported that a slight change in composition results in a shift in the transformation temperatures [33,41,42]

Summary

Introduction

Shape memory alloys (SMA) exhibit displacive and reversible deformation behavior due to sensing thermodynamic and mechanical changes in their environment [1,2,3,4,5,6,7]. This plays a role in the development of components that can be cycled between two macroscopic shapes depending on temperature change. The fact that SMAs exhibit temperature-induced strain recovery makes them a type of advanced engineering material. Even though the Ni-Ti SMA system is widely studied and commercialized on account of its high percentage of shape recovery, Cu-based SMAs have become long-term proposed

Methods

Results

Conclusion