Phase Transformation Study on MP35N Wire

MP35N wire has used to make lead conductor coils and cables in medical devices for more than 30 years because of its excellent fatigue properties, good corrosion resistance and conductivity.  Despite the importance of this alloy, the phase transformation information has not been investigated thoroughly.  The reported phase transformation data on MP35N was based on thick plate samples which require a long dwell time at elevated temperatures to initiate secondary hardening effects.  The thermo-mechanical processes required to form MP35N wire has a set of processing parameters for time and temperature that differ significantly than MP35N plate.  The additional processes performed on wire such as the addition of insulating coatings can have a profound effect on the mechanical properties of MP35N wire.  This work was performed to study the phase transformations on cold drawn MP35N wire.  The results of this work demonstrated that there is an aging response of thin MP35N wire at elevated temperatures.  In this study, the electrical resistivity, mechanical properties, phase diagram, thermal analysis and microstructure (TEM) were analyzed.  A calculated phase diagram of MP35N was created and confirmed by thermal analysis.