Microstructural evolution and compression property of a novel γʹ-strengthened directionally solidified CoNi-base superalloy

Abstract

The microstructural evolution and compression property of a novel γʹ-strengthened CoNi-base superalloy have been investigated. The directionally solidified CoNi-base superalloy possesses a lower density of 9.03 g/cm3 and a higher γʹ solvus temperature of 1166 °C, compared with those of the Co–Al–W-base superalloys with high level of W element. After aging at 900–1100 °C, the alloy displays stable γ/γʹ two-phase microstructure with high volume fraction of the γʹ phase, and without detrimental topologically close-packed (TCP) phase. The CoNi-base superalloy shows good compression property. In the process of compression, the alloy exhibits positive temperature dependence of the 0.2% flow stress above 600 °C. With increasing temperature, the alloy displays a maximum of 0.2% flow stress of 607 MPa at 850 °C. The major deformation mechanisms of the CoNi-base alloy are pairs of a/2<110>-type dislocations shearing γʹ precipitates from room temperature to 850 °C and unpaired dislocations bypassing the γʹ precipitates above the peak temperature of 850 °C. In this alloy, high content of Ni improves the γʹ solvus temperature and microstructural stability, which leads to a good compression property at high temperatures.