V. Martynov, M. D. Bokaie, TiNi Aerospace, San Leandro, CA; A. D. Johnson, G. R. Gray, TiNi Alloy Company, San Leandro, CA
A crystal grower for pulling from a melt of Cu-Al-Ni alloys different single crystalline profiles was designed and built in TiNi Aerospace Company. The grower utilizes Stepanov’s method and enables pulling various profiles (including hollow ones) of oriented single crystals up to 20 inches long. By varying the alloy formulation transformation temperatures of the crystals can be adjusted in the temperature range from –196 to + 200 oC.
Elimination of grain boundaries from the material dramatically improves its mechanical properties and allows single crystals to reach the theoretical limit of strain recovery both in superelastic and shape memory applications of the single crystals. Cylindrical rods and flat profiles of various sizes and transformation intervals have been pulled and tested. Some prospective applications of single crystalline Cu-Al-Ni SMA (SSMA) will be presented and discussed.
Summary: Single crystal copper-aluminum-nickel shape memory alloys tolerate repeated strains of more than 9% in both martensitic and austenitic forms. Our emphasis is on superelastic applications. In superelastic material, the modulus of elasticity is a function of the difference between the austenite finish temperature and ambient temperature, so that stiffness of flexures can be tuned to particular applications.
Anticipated applications include flexures to operate hinge mechanisms in aerospace and energy storage devices.
Funding has been obtained through the SBIR programs of U.S. Navy and DARPA.
