Researchers from the IMDEA Materials Institute have developed a new process to predict and control the microstructure of nickel-based superalloys during metal 3D printing.
The team created a tool that allows manufacturers to control metal powder grain structure by adjusting parameters such as laser power, scan speed, hatch distance, and scan track length. In particular, their efforts focused on controlling the properties of Inconel 939 (IN939) alloy across different processing conditions during laser powder bed fusion (LPBF).
The study, published in the Additive Manufacturing Journal, highlights the importance of melt pool overlap. This is the amount by which one molten track overlaps with the next during laser scanning, determined by the spacing between scan lines.
The researcher found that adjusting the melt pool overlap, perpendicular to both the scan and build directions, changes the size, shape, and orientation of the material’s microstructures.
For example, keeping the melt pool overlap below 0.6 (60%) prevents the formation of long, column-like grains and results in more uniform, fine-grained structures. In contrast, higher overlap leads to columnar grain growth, producing strongly textured internal material patterns.
“This study shows it is possible to locally predict and control the microstructure in a simple and efficient manner,” commented co-author Ignacio Rodríguez Barber, a PhD researcher at IMDEA Materials’ Sustainable Metallurgy Group.
Researchers develop new tool to control metal microstructures
Inconel 939 is a nickel-based superalloy known for its high strength at elevated temperatures and excellent resistance to corrosion and oxidation. These qualities make it an ideal material for manufacturing end-use parts in demanding aerospace and energy applications. However, Inconel 939 is prone to cracking during production, which limits its processability.
The IMDEA researchers’ approach seeks to mitigate these risks by unlocking closer control over material properties. “Our approach not only provides guidelines to obtain excellent printing results, it also enables site-specific design of microstructure for different sections of a part, paving the way for performance-optimized components,” explained Rodríguez Barber.
During their study, the team leveraged both experimental and analytical approaches to demonstrate how microstructures can be predicted and controlled. Their methodology is compatible with high-productivity scanning parameters used in industrial manufacturing, including fast scan speeds, large layer thickness, and a scanning pattern that rotates 67º between layers.
During testing, the researchers fabricated samples using IN939 from German powder manufacturer Eckart TLS GmbH on a Renishaw AM400 LPBF 3D printer. They created two sets of samples. The first set consisted of four 8 x 8 x 8 mm³ cubes, each divided into smaller sections called “domains,” which were produced with different hatch distances.
The results showed that hatch distances of 50 µm (hd50) produced long, column-like grains aligned with the build direction, creating a strong and consistent texture. In contrast, 70 µm hatch distances formed smaller, more randomly shaped grains with a weaker texture.
To better understand how scan track length and hatch distance affect energy input during printing, the team printed “multitrack” samples made of five adjacent laser passes on existing IN939 blocks. They tested 28 combinations with hatch distances from 40 to 100 µm and scan track lengths from 1 to 4 mm. This allowed the team to further explore how different printing conditions influence the material’s structure.
Next, the researchers applied an analytical model based on the Rosenthal equation, originally developed to describe heat flow during welding. They found that both hatch distance and scan track length significantly influence heat accumulation in the metal powder during 3D printing.
Using this insight, the IMDEA team accurately predicted melt pool temperatures, achieving a 93% success rate in forecasting whether the resulting microstructure would be columnar or equiaxed. This distinction is crucial, as grain structure directly affects mechanical properties such as strength and durability in the IN939 superalloy.
The team also developed a refined energy density metric that accounts for scanning geometry and material properties. This advancement enables manufacturers to precisely control microstructures by tweaking laser power and scanning parameters, removing the need for lengthy trial-and-error experimentation.
Research into 3D printing material properties
IMDEA Materials Institute is not the only research body working to improve control over material properties in additive manufacturing.
A team from the California Institute of Technology (Caltech) recently developed a technique to create metallic structures with customized shapes and compositions. This approach offers unprecedented control over alloy design, enabling engineers to tailor materials with specific mechanical and functional properties.
This study, published in Small, builds on earlier work by co-author Rebecca Gallivan using hydrogel-infusion additive manufacturing (HIAM). This process was previously restricted to single-metal prints, but has now been updated to incorporate multiple metals, including copper–nickel alloy fabrication.
Away from metal additive manufacturing, University of Colorado Boulder researchers developed a process to control material properties in inkjet additive manufacturing. Called a “pantone for properties,” the approach combines different resins to create specific material properties.
The team used inverse material design, allowing engineers to specify desired material properties before 3D printing. This enables users to create materials with any combination of stiffness and toughness. The approach holds promise for numerous applications, including the production of realistic synthetic biological tissue.
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Featured image shows IMDEA Materials Institute researcher Ignacio Rodríguez Barber pictured with multiple LPBF-printed IN939 structures. Photo via IMDEA Materials Institute.
