Low temperature creep behavior of directionally solidified superalloys

The critical role of low-temperature creep resistance in gas turbine blade durability drives this investigation into the creep deformation mechanisms of directionally solidified (DS) superalloys at 750 degrees C. Through systematic characterization of composition-orientation-microstructure interactions, fundamental relationships governing the primary creep behavior of CM247LC and DZ411 DS superalloys are established. The results suggest that the standard heat-treated CM247LC superalloy exhibits a pronounced primary creep strain along the <001 > direction, mechanistically attributed to the successive formation and propagation of stacking fault (SF) ribbons. In contrast, DZ411 displays a considerably lower primary creep strain due to the effective suppression of SF ribbon propagation, arising from three synergistic factors: a relatively lower volume fraction of gamma ' precipitates, wider gamma channel, and lower SF energy. Crystallographic orientation analysis uncovers distinct low-temperature creep anisotropy, where transverse specimens show a lower primary creep strain compared to longitudinal creep specimens. This anisotropy originates from orientation-dependent Schmid factors variations in {111}< 112 > slip systems, which further impact the nucleation of SF ribbons. Furthermore, the microstructural degradation after thermal exposure significantly affects the low-temperature creep behavior, as both the nucleation and the propagation of the SF ribbons are altered. The present work enhances our understanding of the low-temperature creep deformation of DS superalloys and is expected to provide insights for optimizing their creep deformation behavior.