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Direct casting and rapid solidification of CuAl SMA wires and characterisation of the microstructure
|Susanne Zeller 1, Joachim Gnauk , Georg Frommeyer|
1. Max-Planck-Instiut für Eisenforschung, Abt. Werkstofftechnik, Max-Planck-Strasse 1, Düsseldorf 40237, Germany
A rapid solidification technique was used to produce thin wires of Cu-Al SMA alloys directly from the melt. In-rotating-liquid-spinning (INROLISP) is an economical and straightforward process to obtain wires in a single-step. In contrast to previous publications a horizontal arrangement of the INROLISP process was used for the direct casting of thin wires. A computer controlled facility was designed and installed to determine and control the near-net-shape casting process and the process parameters over an extended time period. The main process parameters, such as the velocity of the melt jet, the stable free flight length, the nozzle geometry and the cooling rate, were examined. In particular, the meltflow was simultaneously observed by a high speed camera and theoretically described using fluid dynamic equations. After optimization of the process parameters, thin wires of approximately 100 μm in diameter with a reduced grain size were produced. The reduction of the grain size and additions of Ni will depress the martensitic transformation temperature indicating the structural transformation of the high temperature cubic β-phase to martensite. The shape memory properties as the characteristic transformation temperatures of the bulk alloys-ingot samples and of the as cast wires were measured by using differential scanning calorimetry (DSC) and by performing tension tests. The quality of the wires varies with different process parameters and is determined by optical microscopy and scanning electron microscopy (SEM). The effect of rapid solidification on grain size and on the crystalline microstructure of the martensite fraction is demonstrated by EBSD mapping in combination with an EDX scan and XRD analysis based on the Debye-Scherrer technique.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Susanne Zeller
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-10 13:19 Revised: 2009-06-07 00:44