A new post-processing route to improve tensile strength and ductility in 3d-printed alloys

(Press-News.org) In International Journal of Extreme Manufacturing, researchers have developed a dual post-processing method to make 3D-printed metals much stronger and tougher, addressing one of the field's most persistent challenges.

By combining deep cryogenic treatment and laser shock peening, researchers find a new way to transform the microscopic structure of 3D-printed metals, relieving internal stresses and enhancing their mechanical resilience. Their method offers a practical route to producing stronger and more damage-tolerant components for industrial-grade metal additive manufacturing in aerospace, automotive, energy, and defense sectors.

The Hidden Problem in Metal 3D Printing

Laser Powder Bed Fusion (LPBF), the most widely used metal 3D printing technique, allows engineers to design complex, lightweight components that would be impossible to machine by traditional means. Yet, each layer formed by a high-energy laser undergoes rapid heating and cooling, leaving behind residual tensile stresses and irregular microstructures.

"Those stresses are like invisible cracks waiting to grow," explains Prof. Xudong Ren, who led the study. "They make printed metals prone to brittleness and early failure."

Conventional heat treatments can reduce these stresses, but often at the cost of lowering strength. Researchers sought a method that could deliver both high strength and ductility — two properties that typically compete with each other.

A Deep Freeze Meets Laser Power

The researchers turned to a promising material: a metastable high-entropy alloy (Fe₅₀Mn₃₀Co₁₀Cr₁₀) — a complex blend of elements known for combining strength, ductility, and corrosion resistance. Instead of modifying the alloy composition, they focused on its post-processing.

First, the team performed deep cryogenic treatment (DCT) by immersing the printed alloy in liquid nitrogen at −196 °C. The extreme cooling relieved global thermal stresses and refined the microstructure.

They then applied laser shock peening (LSP) — firing high-energy laser pulses onto the surface to generate powerful shock waves that plastically compress and strengthen the material.

"When we combined these treatments, the metal's internal architecture reorganized," says Dr. Zhaopeng Tong, first author of the paper. "We saw a gradient of tightly packed nanocrystals and a reversal of internal stresses — from harmful tensile to beneficial compressive."

From Weak to Resilient

That transformation made a huge difference. The treated alloy showed a switch from tensile to compressive surface stress, peaking at −289 MPa, a surface hardness of 380.8 HV and improved strength and ductility achieved at the same time,

These gains come from a combination of mechanisms working together: microstructural gradients, dislocation hardening, and atomic-level transformations that collectively make the alloy stronger yet more deformable. In effect, it becomes a material that bends instead of breaks.

The Bigger Picture

What makes this research particularly promising is its practicality. Both DCT and LSP are established industrial processes. By sequencing them, the team has demonstrated a sustainable way that manufacturers could adopt with existing infrastructure.

"This integrated strategy lets us fine-tune both the surface and the interior of printed metals," says Ren. "It helps overcome the long-standing trade-off between strength and ductility, which is a central goal in structural materials design."

The researchers are now expanding the technique to other alloys and metal systems, aiming to generalize the approach into a new class of post-processing technologies for high-performance additive manufacturing.

From aircraft engines to medical implants, next-generation manufacturing depends on materials that can endure higher stresses without sacrificing safety, this team may have taken a crucial step toward the future of stronger, safer, and more sustainable metal manufacturing.

International Journal of Extreme Manufacturing (IJEM, IF: 21.3) is dedicated to publishing the best advanced manufacturing research with extreme dimensions to address both the fundamental scientific challenges and significant engineering needs.

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