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After annealing at temperature 550 ºC for 30 minits, MT characteristic temperatures of these alloys are: Ti-50.0 at. %Ni (Ms = 42 ºC, Mf = 39 ºC As = 74 ºC, Af = 65 ºC); Ti – 50,8 at. % Ni (As = (-28 ºC), Af = (-17 ºC)).
The mechanical cycling was carried out according to the scheme: tensioning-unloading, one-sided and two-sided bendings and torsion bending. Failor rate accumulation during the cycling was measured by electrical resistance change and mechanical characteristics qualities changes. Fracture was estimated according to data of optical and electronical mocroscopy investigation.
Resistivity was shown to increase before the hysteresis loop stabilization period (4-7 cycles) during the mechanical cycling at strain (ε < εpl) where εpl – pseudoelastic strain at the plateau-shaped area. Resistivity changes a little during the cycling. Such behavior is a result of deformation hardening. At the stage of full strain returning after unloading the following hardening is absent; it is connected with initiation of reversible austenite – martensite transformation.
Plastic strain at cooling stage takes place already under thermocycling of shape memory alloys. The alloy did not accumulate defects during a heating. Full shape memory effect reversibility is an evidence of this.The paper deals with systematized data of fracture research during the process of different types of cycling deforming. Equations of linear regression showing results of the alloy low-cycle fatigue are represented here. Due to the results of measuring of electrical resistance togeather with mechanical characteristics, we have fixed the period of material critical state, after which the fracture evidently occurs.