Effect of high temperature cyclic loading on γ′ phase evolution behavior of DZ411 alloy

Optical microscopy（OM） and scanning electron microscopy （SEM） methods are employed to investigate the effect of various load conditions—including a constant load of 200 MPa，an average stress of 200 MPa with a stress amplitude of 130 MPa，and an average stress of 150 MPa with a stress amplitude of 130 MPa—on the microstructural evolution of DZ411 alloy. The experimental findings reveal that the dendrite structure remains relatively unchanged under high temperatures and stress conditions. When compared to a constant load，DZ411 alloy subjected to cyclic loading exhibits a reduced number of interdendritic pores，which are also smaller in size. In the absence of loading，the γ′ phase undergoes rafting to form a sheet-like structure. Notably，cyclic loading exhibits a more pronounced promotion effect on the rafting growth process of the γ′ phase than directional constant loading. Additionally，cyclic loading facilitates the merging and growth of small γ′ phase particles，leading to the formation of longer sheet structures as more γ′ phases become interconnected. Furthermore，under cyclic loading，the size and morphological differences among γ′ phase particles become more pronounced.