Deformation mechanisms of a γʹ phase strengthened CoNi-based superalloy at high temperatures

A CoNi-based γʹ phase strengthened superalloy was designed with alloy elements Al, W, Cr, Ti, and Ta added. The size and volume fraction of the γʹ phase can be tailored by the post-heat-treatment, which will then affect mechanical behavior of this alloy. The aged alloy was compressively tested at a wide temperature range, from room temperature to 1000 °C. Detailed microstructural analysis of the tested alloy was carried out using transmission electron microscopy. At 600 °C, the primary deformation mechanism is pairs of a/2 <110> type dislocations and stacking faults shearing in the alloy. The deformation mechanism changed to dislocation pile-ups and climbing in the γ phase when deformed at 800 °C. Further increasing the deformation temperature to 1000 °C, both nanotwins and dislocations were formed and their interactions will be the main strengthening mechanism of the alloy. The deformation mechanism transition and correlated mechanical behavior of this alloy was further discussed based on the defect analysis.