In Situ Study Of Aging Under Stress Of Ni-Ti Shape Memory Alloy

The combined effect of solubilization, hot deformation and precipitation phenomena affect the mechanical behavior and functional properties of shape memory alloys. In order to evaluate the effect of stress on aging phenomena, in situ experiments were conducted with the high energy X-ray diffraction (HEXRD) setup of the HZG beamline (EH3 - P07) at Petra III, DESY, Hamburg. The uniaxial compression aging was carried out under controlled atmosphere in a modified dilatometer Bähr DIL 805 A/D with tensile/compressive stress units. Solubilization at 850ºC, followed by 500ºC annealing, combined with compressive deformation, were analyzed in order to optimize the processing parameters. During the aging step, the volume fraction of Ni4Ti3 increased up to 15 min. After this time, the value of the volume fraction stabilized. This study will enable to identify the most processing routes of NiTi SMA, leading to the adequate functional characteristics for the orthodontic application.