A Crack-Free Additive Manufacturing Strategy for Nickel-Based Superalloys via Composition Design and Process Control

In the preparation of high γ' phase strengthened nickel-based superalloys prepared by laser powder bed fusion (LPBF), the high crack susceptibility caused by rapid solidification restricts their high-temperature service performances. Taking Inconel 939 (IN939) as an example, we systematically analyze the crack formation mechanism and its inhibition mechanism, and propose a component-process collaborative optimization strategy. Based on the thermodynamic calculations and the solidification crack susceptibility index (SCI) model, it is confirmed that the increasing the Si mass fraction can reduce the tendency of liquid film rupture between dendrites and reduce the solidification crack occurrence. Reducing the Al content can effectively inhibit the aging precipitation of γ' phase, thereby reducing solid-state cracks. When the mass fractions of Si and Al are 0.5% and 1.0%, there is a good balance between the crack density and mechanical properties. On this basis, optimizing the laser input to refine grain, promoting grain equiaxed degree and weakening texture can further inhibit the initiation of cracks. When the laser power is 220 W, and the scanning speed is 800 mm/s, IN939 alloy with no cracks and porosity is below 0.1% can be prepared. This study provides approaches and insights for composition design and process optimization of the additive manufacturing of γ'-strengthened nickel-based superalloys.