Analysis of temperature-induced dominant mode transition and transgranular small fatigue crack propagation behavior in FGH96

In-situ experiments were carried out using the powder metallurgy superalloy FGH96 to observe the evolution of small fatigue cracks under different thermal and mechanical loading scenarios. Electron backscatter diffraction was subsequently employed to assist in the analysis of how changes in temperature and stress levels influence the growth behavior of small fatigue cracks. The influence mechanisms of crystallographic parameters (Schmid factor and geometric compatibility factor) on small fatigue crack propagation were quantitatively examined. During the study, a temperature-induced transition in the dominant crack propagation mode was observed in FGH96, occurring between 600 and 700 °C. Specifically, the dominant mode changed from transgranular to intergranular propagation. Within the temperature range from room temperature to 600 °C, neither temperature nor applied stress level showed a noticeable effect on the relationship between the Schmid factor of the activated slip system and the maximum Schmid factor. Under these conditions, small fatigue cracks followed a consistent propagation mechanism governed by the Schmid factor. The Schmid factor emerged as a key parameter in controlling the transgranular propagation behavior of small fatigue cracks in FGH96, whereas the role of the geometric compatibility factor appeared to be limited.