Effect of heat treatment on rotating bending fatigue properties of K417G nickel-base superalloy

By observing the microstructure, testing the rotating bending fatigue property and analyzing the microscopic deformation characteristics, the effects of heat treatment on grain boundary carbides and rotating bending fatigue property of the K417G nickel-based superalloy were studied. The results show that the rotating bending fatigue property of the alloy is improved by adjusting the precipitation characteristics of grain boundary carbides through the appropriate heat treatment. After aging at different temperatures (850 °C, 900 °C and 950 °C) for 16 h, the previous Zr-rich carboborides at grain boundaries in the as-cast alloy were transformed into M23C6 carbides rich in Cr and Mo. With the increase of aging temperature, the grain boundary carbides gradually changed from continuous chains to dispersed spherical and ellipsoidal grains. The average spacing size of the grain boundary carbides gradually increased from 0.57 µm to 0.74 µm, and the distribution of carbides along the grain boundaries became more and more dispersed and uniform. In the alloys aged at 850 °C and 900 °C, severe dislocation pile-up and stress concentration around the continuous carbide chains at grain boundaries promoted the initiation and propagation of microcracks, resulting in low rotational bending fatigue property. When the alloy was aged at 950 °C, the dispersed grain boundary carbides could not only effectively hinder the grain boundary sliding, but also significantly reduce the dislocation pile-up and stress concentration around the carbides, thereby the rotating bending fatigue property of the K417G superalloy was improved.