Fabrication of super invar micro- and nano- structures by electrodeposition for low thermal expansion applications

Abstract

Electrodeposited alloys of Super Invar composition, 64 wt % Fe, 31 wt % Ni, and 5 wt % Co, are of both theoretical research and practical interest due to the anomalous codeposition behavior, the preferential deposition of less noble metal, and to the material's low coefficient of thermal expansion, CTE. A better understanding of anomalous codeposition allows for controlling the deposition rates of individual Fe, Ni, and Co metal during codeposition and hence the composition. In addition, electrodeposited Super Invar alloys are of practical interests due to their potential applications in industry, particularly in micro-electro-mechanical systems (MEMS) due to the material's near zero CTE at room temperature in bulk materials. In practice, however, it is difficult to predict the alloy composition and control the composition gradient along the direction of growth, due to the anomalous codeposition behavior. Super Invar has not been widely studied; most studies of the ternary FeNiCo have been focused on Co-rich alloys due to their magnetic property over the last twenty years. In addition, there is an absence of understanding the CTE in electrodeposited Super Invar structures and how it is influenced by the electrodeposition parameters.