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Influence of micro-EDM on the phase transformation behaviour of medical-grade nitinol

Einfluss von µ-Drahterodieren auf das Umwandlungsverhalten von medizinischem Nitinol
 
: Mwangi, James Wamai; Weisheit, Linda; Bui, Viet Duc; Zanjani, Matin Yahyavi; Schubert, Andreas

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Shape memory and superelasticity 4 (2018), Nr.4, S.450-461
ISSN: 2199-384X (Print)
ISSN: 2199-3858 (Online)
Englisch
Zeitschriftenaufsatz
Fraunhofer IWU ()
micro-EDM; Nitinol; phase transformation behaviour; shape memory; superelasticity; Differential Scanning Calorimetry (DSC); JET-ECM

Abstract
Most nitinol medical applications are hinged on its superelasticity and shape memory—two unique properties that are dependent on nitinol’s phase transformation between a martensitic phase and an austenitic phase. Since these transformations are thermomechanical in nature, establishing the influence of thermal processing on nitinol’s phase-transformation behaviour is vital as this can help in predicting changes and/or tuning its mechanical properties to fit specific applications. This study uses differential scanning calorimetry to investigate the influence of micro-electrical discharge machining (micro-EDM) on nitinol’s phase-transformation behaviour. For conclusive analysis, a relatively a thermal Jet-ECM process is used as a reference for the as-received material, whereas Laser, a more commercially established medical-grade nitinol machining process, is used to provide comparative analytical aid. From the results, it can be clearly shown that high discharge energies in micro-EDM do indeed have the potential to significantly alter nitinol’s transformation behaviour, including reducing thermal hysteresis and resulting in the occurrence of an unusual three-peak phenomenon in the endothermic reverse transformation on heating.

: http://publica.fraunhofer.de/dokumente/N-541184.html