Effects of heating cooling rate and cooling method after aging on the thermal properties of Ni-rich NiTiNb alloy with low Nb

In the present study, the effects of heating-cooling rate and the effects of cooling method after aging on the thermal properties of Ni-rich NiTiNb alloy containing low Nb element were investigated. Specimens were aged at 823 K (550 degrees C) for 5 h and cooled in two media: furnace and water. X-ray diffraction, differential scanning calorimetry, hardness measurement, scanning electron microscopy and compression tests were carried out. Two-step phase transformation during cooling was observed due to the nickel-rich precipitates. The activation energies of the alloys were calculated according to the Kissinger, Takhor, and Ozawa methods. The results indicated that cooling method after aging has a strong effect on the transformation temperatures. The austenite peak temperatures of WQ and FC specimens are 266.4 K and 320.6 K, respectively, at 10 K min(-1) heating-cooling rate. A higher critical stress value of 404 MPa was obtained to initiate the martensitic transformation for the WQ specimen compared to the FC specimen (152 MPa).