Influence of oxygen content on fatigue crack growth behavior of FGH96 superalloys

Abstract

The fatigue crack growth (FCG) mechanism of FGH96 superalloys influenced by oxygen (O) was investigated in terms of grain structure and phase composition. The results reveal that the thinner powder oxide film process facilitates easier dissolution, and thus the fewer undissolved oxides as well as the movement of high-angle grain boundaries promote the generation of a uniform distributed small grains (SGs) within both the prior particle boundaries (PPB) interface and powder interior in the alloy with O content of 140 ppm. In contrast, the large number of undissolved oxide particles provides more recrystallization sites and thus the SGs clusters aggregate at the PPB interface in the alloy with O content of 340 ppm during sintering. A homogeneous distribution of SGs induces the uniform deformation of the alloy and thus stimulates the transgranular fracture of the coarse grains in alloy with O content of 140 ppm, in favor of a higher fatigue life. On the contrary, in the alloy with O content of 340 ppm, the SGs clusters forming on PPB interface results to the strain concentration at PPB, leading to the PPB fractured morphology and a serious reduction of the fatigue life. This study reveals that the generation of SGs is responsible for the FCG behavior and failure mechanism of the alloys, and suggests that regulating the uniform distribution of SGs or reducing the number of SGs during sintering plays an important role in improving the fatigue properties of powder metallurgy superalloys.