Laser additive manufacturing technology merges design and production, incorporating crucial elements such as materials, structure, process, and performance. This integration offers an efficient and cost-effective way to create prototypes and test new designs. It plays a vital role in manufacturing and repairing complex parts comprising nickel-based superalloys. However, this technology faces challenges with traditional high-strength nickel-based superalloys. The differences in composition and strengthening mechanisms, along with the rapid solidification and phase transitions unique to laser additive manufacturing, can lead to issues. The high alloying degree causes a wide solidification temperature range, while the abundance of intermetallic compounds leads to varying strength and ductility at high temperatures. This in turn increases the risk of microcrack defects. These defects can degrade the quality and mechanical properties of γ′ phase strengthened nickel-based superalloys produced through this method. Therefore, understanding the characteristics, formation mechanisms, and influencing factors of cracks, as well as recognizing the crack control methods and related achievements, can lay a theoretical foundation for exploring universal crack resistance pathway and composition design of superalloy matching additive forming characteristics.

This paper offers an in-depth exploration of various crack types in γ′ phase strengthened nickel-based superalloys used in laser additive manufacturing, including the morphology and mechanisms of solidification cracks (Fig.2), liquation cracks (Fig.3), ductility-dip cracks (Fig.5), and strain aging cracks (Fig.6). It elucidates the connections between the solid phase fraction and index for solidification cracking susceptibility, the differential scanning calorimetry curve and liquation sensitivity, the relationship between alloy ductility and the temperature range for ductility dip, as well as the link between γ′ phase forming elements and the risk of strain aging cracking. The discussion includes common strategies for enhancing crack resistance, such as modifying the composition to alter solidification characteristics and minimize or eliminate the formation of low-melting-point phases (Fig.8), introducing second-phase particles to encourage the shift from columnar to equiaxed crystal growth, thereby altering the residual stress state (Fig.9), and optimizing laser processing parameters to directly improve microstructure and forming quality (Fig.10). Furthermore, post-treatment methods significantly contribute to reducing cracking tendencies and enhancing the mechanical properties of superalloys. The ultimate approach to addressing the cracking issue involves developing nickel-based superalloys with specific compositions tailored for laser additive manufacturing. Recent successes in designing crack-free new alloys have leveraged tools such as thermodynamic calculations (Fig.11), machine learning (Fig.12), the cluster structure model (Fig.13 and Table 2), and the multi-principle-element concept (Fig.14). The shift from empirical to scientific and rational design in material research is being advanced by the use of phase diagram calculations for alloy design, supported by reliable thermodynamic databases. Machine learning facilitates the rapid development of mathematical models that quantitatively link material composition, processes, structure, and properties, enabling precise screening of target materials. The cluster structure model offers insights into how alloy elements’ type and amount affect formability. Meanwhile, the multi-principle-element concept emerges as an efficient strategy for simultaneously enhancing crack resistance and the strength-ductility balance. In summary, this paper’s overview of advancements in crack control and composition design for γ′ phase strengthened nickel-based superalloys in laser additive manufacturing offers practical insights for the future creation of printable, high-temperature, high-strength nickel-based superalloys and their components (Fig.15).

Significant progress has been made in controlling cracks in γ′ phase strengthened nickel-based superalloys for laser additive manufacturing, laying a theoretical and methodological foundation for creating crack-free superalloys through laser processing. Despite these advancements, developing precipitation-strengthened nickel-based superalloys and their components that maintain high-density forming, along with stable microstructure and performance in high-temperature environments, remains challenging. Future research should focus on several key areas. First, it is crucial to understand the fundamental differences in cracking mechanisms between different alloys. Establishing a clear link between the types and contents of γ′ strengthening elements, their interactions, and their impact on crack sensitivity will aid in developing universal crack prevention and control strategies for similar alloys. Second, it is vital to develop swift design criteria for alloy compositions that align with desired performance and printability, establishing a distinct system of γ′ phase strengthened nickel-based superalloys tailored for laser additive manufacturing. Third, enhancing the understanding of the alloys’ resistance to creep, fatigue, corrosion, thermal shocks, and the long-term stability of their microstructure and performance at high temperatures will further promote their adoption in critical sectors such as aerospace and nuclear power, among others. Finally, achieving mold-free manufacturing of crack-free nickel-based single crystal superalloys with superior overall performance, alongside the production of large, precise, and complex structural components, is essential. This advancement aims to fulfill the demanding conditions of aircraft engines operating at higher temperatures and in more severe environments.