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

摘要

The microstructural evolution and compression property of a novel gamma'-strengthened CoNi-base superalloy have been investigated. The directionally solidified CoNi-base superalloy possesses a lower density of 9.03 g/cm(3) and a higher gamma' solvus temperature of 1166 degrees C, compared with those of the Co-Al-W-base superalloys with high level of W element. After aging at 900-1100 degrees C, the alloy displays stable gamma/gamma' two-phase microstructure with high volume fraction of the gamma' 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 degrees C. With increasing temperature, the alloy displays a maximum of 0.2% flow stress of 607 MPa at 850 degrees C. The major deformation mechanisms of the CoNi-base alloy are pairs of a/2 110 -type dislocations shearing gamma' precipitates from room temperature to 850 degrees C and unpaired dislocations bypassing the gamma' precipitates above the peak temperature of 850 degrees C. In this alloy, high content of Ni improves the gamma' solvus temperature and microstructural stability, which leads to a good compression property at high temperatures.