In aircraft engines, nickel-based superalloys are extremely important — they make up about half the weight of the engine because they can withstand very high temperatures and stress. One such alloy is Inconel 718 (IN718), valued especially for its creep resistance — that is, ability to resist deforming when exposed to high heat for long periods. This makes it ideal for jet and rocket engine parts.
However, when IN718 is made using additive manufacturing (AM) — a 3D printing-like process — its creep resistance is worse than when made the traditional way (called ‘wrought’ processing).
The reason for that wasn’t clearly understood — until now.
Researchers at IIT-Madras have discovered both the cause and the solution.
They found that in AM-processed IN718, a metal called niobium doesn’t spread evenly. Instead, it gathers at the grain boundaries — the microscopic zones between crystal-like regions in the metal. This unevenness creates soft spots next to the grain boundaries, known as precipitate-free zones (PFZs), which are weak and reduce the metal’s ability to withstand creep.
In traditional methods, these problems are fixed later, during the forging and heating steps, which helps niobium spread evenly. But in AM, where parts are printed directly to shape, this step is skipped, and the segregation problem remains.
To fix this, the researchers tried heating the AM metal to a higher temperature (1,150 degrees C) than usual, giving niobium atoms more energy to move and spread out. They carefully balanced this to avoid damaging the metal’s structure. “The long-term exposure heat treatment methodology demonstrates that PFZs are the major influencing factor responsible for microsegregation-dependent creep rupture behaviour,” the scientists say in a paper.
The new treatment successfully removed the soft PFZs and made the material much more creep-resistant — improving its performance by five times compared to the standard heat treatment.
This breakthrough could make 3D-printed IN718 parts practical for real-world use in aircraft and space engines.