• Additively manufactured Titanium-Iron (Ti-Fe) alloys offer high-strength properties at elevated temperatures and a favourable strength-to-weight ratio.
• Their potential to be utilised in the manufacture of complex 3D-printed components couples with the potential for a lower-cost alternative to traditional high-temperature alloys.

Developing metals specifically for additive manufacturing, also known as metal 3D printing, is increasingly important. This process imposes thermal conditions and solidification rates that differ significantly from conventional fabrication methods.

At IMDEA Materials Institute, Dr JoAnn Ballor is leading UTIFE, a Marie Skłodowska Actions Postdoctoral Fellowship project focused on ultrafine, hierarchically structured eutectic Ti–Fe alloys designed for these conditions.

Dr. Ballor is studying these alloys using selective laser melting (SLM) together with advanced tomographic techniques to observe how their microstructures evolve during printing, and how defects such as cracks can form or be mitigated.

Designing new metals for additive manufacturing

As it remains a relatively novel manufacturing technique, many of the alloys used in 3D printing were originally designed for more traditional fabrication methods such as casting, forging or machining.

These processes involve relatively slow, predictable temperature changes. This contrasts with additive manufacturing, which melts the metal powder with a pinpoint laser, cooling it again at extraordinary speed in every new layer.

“Heat changes how the internal structure of a metal forms,” explains Dr Ballor. “And SLM exposes every layer of the part to extremely fast heating and cooling cycles. If we only rely on alloys developed for traditional manufacturing in more advanced 3D-printing processes, we risk overlooking entirely new compositions with novel behaviours and properties.”

The promise of Ti-Fe-based eutectic alloys

The ultrafine eutectic Ti-Fe alloys at the heart of the UTIFE project were originally designed for high-temperature aerospace applications. Their appeal lies in their ability to form a unique ultrafine eutectic structure through the entire part, a feat made possible only through additive manufacturing’s rapid cooling.

In this context, eutectic structures provide two key benefits: a stable, ultrafine microstructure, and uniformity across the entire printed component. This avoids weak points or phase segregation that can occur in non-eutectic alloys, improving reliability.

“In the previous ELAM project aimed at developing new high-strength eutectic alloys, and in which IMDEA Materials played a key role, one particular Ti-Fe alloy with ultrafine eutectic structures performed better than other alloys designed for similar applications at temperatures up to 450°C,” says Dr. Ballor.

“However, one key challenge these alloys still face is cracking. While they can be printed at high temperatures outside the range of commercial SLM systems, when printed in the commercial temperature range (room temperature to 400°C) cracks form during printing.”

“This is a significant challenge as crack-free pieces are critical for aerospace applications. Resolving this is the focus of UTIFE,” she adds.

Improving the reliability of metal 3D printing

The SLM being utilised within the project offers two key advantages: an ability to generate ultrafine microstructures unattainable by traditional routes, and the possibility of repairing cracks as layers are built.

Dr Ballor’s work investigates how cracks initiate, grow and interact with the molten material, and how the process itself may allow them to be effectively “healed” in situ. These insights will help pave the way toward commercialisation of Ti-Fe-based alloys.

This research also holds relevance for other crack-prone alloys.

“Once we really understand how defects form and evolve during SLM,” she notes, “we can make additive manufacturing more predictable and reliable, increasing its appeal in commercial use.”

Looking inside materials as they form

A distinguishing feature of UTIFE is the use of in-situ synchrotron X-ray computed tomography (S-XCT) alongside high-speed X-ray radiography, powerful imaging techniques capable of seeing inside the alloy while it is being printed.

Synchrotron X-rays have sufficient energy to visualise tiny defects such as cracks or pores inside the metal.

“Meanwhile, these radiography techniques provide us with a high-speed 2D video of the metal powder as the laser melts it into a solid sample and lets us watch defects like the cracks form in real time,” explains Dr. Ballor. “This is a view that is impossible to capture with any other current technique”.

In-situ tomography then reconstructs a 3D image of the printed layer after each pass of the laser, showing how cracks evolve as the material melts, remelts and cools.

By combining these two techniques, researchers can build a detailed picture of microstructural evolution at multiple scales, from the nanoscale to the macroscopic.

In doing so, Dr. Ballor hopes to come closer to understanding the mechanisms of crack formation, porosity and healing, provide multiscale 3D characterisation of the microstructure, and to define clear processing-microstructure-property relationships.