Effect of nitrogen content on the microstructure and mechanical properties of a cast nickel-base superalloy

The effects of nitrogen content on the microstructure and the mechanical properties of a cast nickel-base superalloy (CNS) have been investigated experimentally. Experimental results demonstrated that the grain structure of CNS samples was refined by increasing the nitrogen content, but the area percentage of microporosity has been augmented with increased nitrogen content. Increasing the nitrogen content resulted in the morphology evolution of carbide from an acicular or ‘Chinese hieroglyphs’ type to blocky one, while negligible change of the morphology of γ′ precipitates was observed. Finally, it was found that the tensile strength has no obvious variation as the nitrogen content increases from 5 to 26 ppm, but it reduces sharply when the nitrogen content is raised to 34 ppm. The elongation decreases gradually with increasing nitrogen content.