Investigating 3D-printed metals for aeronautical engineering

UL’s Dr Kyriakos Kourousis discusses his current research in metal additive manufacturing and the work of the Metal Plasticity and Additive Manufacturing Group at UL.

Dr Kyriakos Kourousis is an associate professor in aeronautical engineering at University of Limerick (UL), as well as director of postgraduate research and education for the university’s Faculty of Science & Engineering. He also leads UL’s Metal Plasticity and Additive Manufacturing Group.

Kourousis joined UL’s School of Engineering 12 years ago, and before his career in academia, he spent more than a decade as an aeronautical engineer in the Hellenic Air Force working on aircraft maintenance, airworthiness and structural integrity – experience that he says now shapes his research and teaching.

At UL, he teaches topics around aircraft systems, the airworthiness of aircraft and the practical engineering behind them.

In terms of his current research, Kourousis says his work focuses on two things: how metals behave when they are loaded in a repeated way, leading to permanent deformation – “what engineers call metal plasticity” – and how to make and trust 3D‑printed metal parts (metal additive manufacturing), “especially for those loading conditions that cause plasticity”.

“In simple terms, we test metals, study their microstructure, build computer models that predict how they’ll perform over time, and use those models to predict how permanent deformation builds up during their operation,” he tells SiliconRepublic.com.

“Localised permanent deformation (plasticity) is the origin of fatigue in metals. My work is both on traditional metals and 3D‑printed ones.”

Here, Kourousis tells us about his work and provides a look into the world of 3D-printed materials and aeronautical engineering.

Why is your research important?

As 3D‑printed metal parts move from prototypes to real aircraft and machinery, we need to predict their behaviour with confidence. Experimental data and models help engineers design parts that won’t crack or fail early, and help industry and regulators build the evidence needed for certification. In short, better predictions mean safer, lighter, more efficient products.

Also, from a sustainability point of view, the use and reuse of powder in metal additive manufacturing offers an important advantage over other (traditional) manufacturing processes. However, with each reuse cycle, the recycled powder changes its synthesis and overall ‘quality’, which can have an effect on the produced parts, especially in terms of their plasticity behaviour.

What has been the most surprising/interesting realisation or discovery you’ve uncovered as part of this research?

One key finding is how directional 3D‑printed metals can be and what causes this directionality. For example, we showed that changing the build orientation and the post-3D printing processing of steel parts via heat treatments can noticeably change how it stretches and yields. We saw similar effects in 3D-printed titanium, in particular Ti‑6Al‑4V, which is widely used in the aerospace and biomedical industries.

We’ve also found that even lower‑cost metal 3D printing routes (like material‑extrusion/fused filament fabrication) show clear links between print settings and mechanical performance, useful for small/medium companies exploring affordable metal additive manufacturing.

What are some common misconceptions of your research area?

3D‑printed metals aren’t ‘just like’ traditional (wrought) metals. The layer‑by‑layer process creates a directional ‘grain’, so properties change with build direction, clearly shown in our work on steel and titanium. Process signatures matter. Printing can leave tiny pores (lack‑of‑fusion or keyhole) and locked‑in residual stresses; tuning scan strategy and energy helps, but these features still drive plasticity and fatigue if not managed.

An interesting debate I have with colleagues working in material science is that 3D-printed material may appear as having uniform features in the microscale, but the higher scale defects caused by the melting-solidification and re-melting can lead to a quite non-homogeneous part with differing mechanical properties at different loading directions (mechanical anisotropy).

Post‑processing can close the loop. Ageing/stress‑relief and especially hot isostatic pressing (HIP) homogenise the microstructure and seal pores, boosting ductility and fatigue, though outcomes depend on the as‑built quality and the budget available. A key target for the manufacturing industry is to make 3D printing not only accurate and consistent but also affordable, and we see that there is more work that has to be done there.

What has been the most significant development in your field since you started your academic career?

The big shift is the coming‑together of accessible metal 3D‑printing equipment with advanced, physics‑based modelling.

At UL, a milestone was obtaining a GE Concept Laser Mlab Cusing R metal 3D printer through a GE Additive award. Unlike other institutions in Ireland, our 3D printer is hosted within an industrial environment, through a collaborative agreement with our partner, Croom Medical. Our students and researchers can test ideas under realistic conditions, while both UL and Croom Medical leverage the advantages of this strategic partnership.

Can you tell me a bit about the Metal Plasticity and Additive Manufacturing Group at UL?

Our research group leads the metal additive manufacturing research activity in UL.

Our work is built around two main strands: metal plasticity modelling, where we turn lab data into reliable models of how metals actually deform; and metal additive manufacturing, where we study and improve metals such as titanium and steel, translating the results into practical build and heat‑treatment guidelines. Current projects and student work span physics‑informed yield prediction for steel 316L, laser powder bed fusion (the most widely used additive manufacturing method for metals) process optimisation, and corrosion-cyclic plasticity topics for aerospace‑grade alloys.

An interesting recent work involved showing that, by carefully retuning laser power, scan speed and hatch spacing, we can shift from the usual thin‑layer settings to much thicker layers in laser powder bed fusion of aerospace‑grade titanium, while keeping the process stable and parts dense. Led by one of our doctoral researchers who also works with Croom Medical, the study showed that those thicker‑layer builds delivered strength and ductility on a par with conventional settings, indicating that productivity can rise without an automatic hit to material performance.

Most importantly, after standard vacuum heat treatment and hot‑isostatic pressing, the parts satisfied the relevant industry standards, pointing to a practical path to higher throughput that still fits certification expectations.

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