A practical method for microstructure control in 3D printed Ni-based superalloys

Nickel-based superalloys, such as Inconel, are among the most promising yet challenging materials in additive manufacturing. These materials are renowned for their remarkable strength and resistance under extreme conditions; however, their complexity also presents a significant challenge in controlling their internal microstructure during printing. Understanding and manipulating this microstructure is vital, as it directly influences the mechanical performance, durability, and reliability of the manufactured parts. That is the goal of a recent study conducted by a group at the IMDEA Materials Institute, led by Ignacio Rodríguez Barber and focusing on INconel 939. The study was published in the Additive Manufacturing Journal.

The critical role of Ni-based superalloys in industry

Nickel-based superalloys play a crucial role in various high-performance industries. Their ability to withstand elevated temperatures and corrosive environments makes them essential in sectors such as aerospace and energy production. Components made from these alloys are often exposed to intense operational conditions, such as those found in gas turbines and jet engines, where material failure is not an option. Despite their benefits, the very properties that make them so useful also contribute to their difficulty in manufacturing, especially when attempting to achieve precise and uniform grain structures across complex geometries.

The LPBF process, while highly versatile and precise, introduces rapid thermal fluctuations that lead to complex and often unpredictable grain structures. The inability to consistently predict and control these microstructures can compromise the performance of the final product. Conventional approaches have largely relied on iterative, trial-and-error experimentation, which limits efficiency and increases production costs. The industry has long awaited a method that offers both predictive capability and scalability for controlling microstructural properties.

The Sustainable Metallurgy Group, under the leadership of María Teresa Pérez-Prado, is dedicated to solving critical challenges in metal processing. The group has developed a practical methodology that enables precise microstructural control during the LPBF of nickel-based superalloys. This approach introduces a significant breakthrough by identifying melt pool overlap as a key geometric parameter that can be adjusted to achieve desired microstructural outcomes.

IMDEA’s vision for IN939

The specific focus of the study is IN939, a high-performance nickel-based superalloy commonly used in aerospace and energy applications. It exhibits exceptional resistance to high temperatures, oxidation, and creep deformation. These attributes make it suitable for applications that demand prolonged exposure to harsh conditions. However, IN939 also presents a narrow processing window and a high tendency to crack during solidification, making it difficult to process effectively through LPBF without introducing structural defects.

The central innovation of the study lies in the detailed examination of melt pool overlap, which is the extent to which adjacent laser paths intersect during the LPBF process. By systematically modifying this overlap, the researchers were able to influence grain size, shape, and orientation within the printed material. Low overlaps, below 0.6, resulted in a fine-grained, equiaxed structure that is more uniform and less prone to cracking. In contrast, higher overlaps promoted the growth of elongated, columnar grains with strong texture. This discovery opens the door to local microstructure control, allowing engineers to tailor the internal properties of different regions within a single part.

To strengthen their findings, the IMDEA team combined hands-on experimentation with advanced modeling techniques. They reformulated Rosenthal’s equation, traditionally used for thermal conduction predictions, to better suit the dynamic conditions of LPBF. Additionally, they developed a new interpretation of normalized volumetric energy density, helping to explain how energy inputs interact with the material during processing. These models enhance the accuracy of microstructural predictions and provide a more robust framework for designing process parameters.

This research has yielded a predictive tool that enables manufacturers to define and adjust process parameters with unprecedented precision. Variables such as laser power, scan speed, hatch distance, and scan track length can now be directly correlated with microstructural outcomes. The ability to fine-tune these parameters enables the fabrication of components that are optimized not only in shape and dimension but also in material behavior, adapting to the specific demands of each section of the part.

Targeting industrial production

Unlike many academic solutions that remain confined to laboratory settings, IMDEA’s methodology is fully compatible with industrial-scale production. It works seamlessly with fast scanning strategies, large layer thicknesses, and standard scanning patterns such as meander paths with rotational shifts between layers. This ensures that the process remains efficient and scalable, meeting the productivity requirements of large-scale manufacturing while maintaining quality and structural integrity.

The practical implications of this work are substantial. By allowing localized control of grain structure, engineers can design components with superior performance characteristics, such as improved fatigue resistance in critical stress regions or enhanced thermal conductivity where needed. This research not only advances the science of materials engineering but also creates opportunities for innovation in component design across various sectors, including aviation, power generation, and space exploration.

This study received significant support from the Spanish Ministry of Science, Innovation and Universities under project PID2019–111285RB-I00. Lead researcher Ignacio Rodríguez Barber conducted the work as part of an FPI fellowship (PRE2020–094256) awarded by the same ministry. Their backing has been crucial in enabling this cutting-edge research to progress from theoretical exploration to practical applications.