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).

Automated summary

This study investigates the effect of heating-cooling rate and cooling method after aging on the thermal properties of Ni-rich NiTiNb alloy. The results show that the transformation temperatures of the alloy vary depending on the cooling method.