Stress Evolution in Sputter-deposited Fe–Pd Shape-memory Thin Films

Abstract

Fe–Pd films with Pd content varying between 26 and 30 at.% have been deposited by means of magnetron sputtering of elemental Fe and Pd targets. As-deposited films are highly supersaturated solid solutions of Pd in Fe that have a body-centered-cubic crystal structure and a very fine grain size. Substrate curvature measurements indicate that the films undergo an irreversible densification when heated above 100 °C. This densification is attributed to a structural change that is also observed in other supersaturated systems with a substantial atomic size difference between the constituents. It is possible to retain the high-temperature austenite phase at low temperature by annealing the films at 900 °C followed by rapid cooling. Depending on film composition, this metastable austenitic phase transforms to either a body-centered tetragonal (bct) or a face-centered tetragonal (fct) martensite around room temperature. Substrate curvature measurements show that formation of the fct martensite is reversible, while that of bct martensite is not. The fct transformation occurs at lower Pd content and higher temperature than reported for bulk materials. Both the fct and the fcc phase show a strong Invar effect at lower temperature and Pd content than observed in the bulk.

Microstructure of pulsed laser deposited FePd thin films on amorphous and crystalline substrates

“…These grain sizes are of the same magnitude as reported previously for sputtered FePd thin films [1,17].…”

High-throughput analysis of thin-film stresses using arrays of micromachined cantilever beams

“…Figure 6 shows the variation of the residual stress as a function of Pd content in the as-deposited Fe-Pd thin-film alloy. It is evident from the figure that the residual stress values are in very good agreement with measurements on similar Fe-Pd films by Sugimura et al 14 and that the stress increases slightly with increasing Pd content.…”

“…This heat treatment results in a coating with a face-centered-cubic structure, which is normally only found at elevated temperatures. 14 The SiN x on the cantilever beams prevented the formation of silicides through reaction of the Fe-Pd with the underlying silicon during the heat treatment. After the heat treatment, the curvature of the cantilever beams was measured as a function of temperature between room temperature and 120°C by using the heating stage in the substrate curvature apparatus.…”

High-throughput screening of magnetic properties of quenched metallic-alloy thin-film composition spreads

“…Fe 70 Pd 30 , as discussed above, is a well-known FSMA when it is annealed at high temperatures and then quenched [1]. There have been several reports of synthesizing single composition thin-film samples of this system by quenching [7,8]. However, to our knowledge this has not been attempted with composition spreads.…”