Gözenekli Niti Alaşımların Üretimi ve Karakterizasyonu
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Ni50.6Ti49.4 specimens with %36, %55 and %60 porosity were produced by using space holder and conventional sintering method. Pure magnesium was used as a space holder and specimens were sintered at 1100C for 1 hour and at 1200C for 2 hours. Sintered %36, %55 ve %60 porous Ni50.6Ti49.4 specimens were subjected to isobaric (under constant stress) cooling-heating experiments to determine the shape memory properties such as recoverable and irrecoverable strain levels and thermal hysterisis. Besides, Differential Scanning Calorimetry (DSC) was used for determining the transformation temperatures. Due to the high strength of the sintered 36% porous Ni50.6Ti49.4 alloy, recoverable strain up to 4.5% and no irrecoverable strain up to 100 MPa of applied stress levels were observed. Thermal hysterisis of this sample under constant stress levels was determined as very low. Furthermore, as the porosity percentage of the specimens increases, irrecoverable strain levels under low constant stress levels increase. Since the strength of the %60 porous Ni50.6Ti49.4 alloy decreaseses, it fractures at a relatively lower stress level.