How ESA’s new 3D printing method is trying to solve one of the toughest problems in modern metal manufacturing
The development of metal 3D printing in recent years has opened the way to producing parts that are geometrically complex, lighter, and functionally more advanced than those obtained through conventional machining processes. However, as soon as an attempt is made to combine several different metals in the same piece, the industry encounters a problem that has proven far more difficult than printing precision itself. High stresses arise at the boundaries between materials, brittle interphases develop, and cracks appear that can completely compromise the part. It was precisely this problem that a European Space Agency project, led by EPFL, addressed, and its results indicate that combining metal powders with thin metal foils could open a new phase in multi-material additive manufacturing. This is a topic that matters far beyond the laboratory, because the need to combine strength, low mass, thermal conductivity, and corrosion resistance at the same time appears in the space, energy, biomedical, and high-tech industries.
Why joining different metals in 3D printing is so complex
Laser Powder Bed Fusion, often abbreviated as LPBF, is today among the most advanced methods for producing complex metal parts. The process is based on a laser selectively melting very thin layers of metal powder, layer by layer, until the finished part is built. The advantage of this approach is an exceptionally high degree of design freedom: it is possible to obtain internal channels, lightweight lattice structures, and components that would be difficult or too expensive to produce using conventional methods. However, when materials with very different properties are combined in the same build, for example titanium and aluminium alloys, the thermal regime becomes much more aggressive. Differences in melting point, thermal expansion, conductivity, and chemical reactivity create conditions in which intermetallic compounds form at the contact between the two materials, and these can be extremely brittle.
In practice, this means that the very idea of multi-material printing is not enough if the transition between two alloys cannot withstand stresses during manufacturing and later use. The ESA project started from the fact that some combinations under such conditions are considered so-called unweldable. This does not mean that it is absolutely impossible to join them, but rather that under normal process conditions cracking, porosity, or layer separation occur very easily. According to the project description on ESA’s activities portal, previous attempts to extend LPBF to multiple materials have generally moved in the direction of upgrading systems for depositing several types of powder or introducing multiple lasers for processing different materials within the same layer. The problem is that such approaches often lead to large mixing zones, and it is precisely in these zones that pores, cracks, and unfavourable microstructure easily form.
From powder mixing to a hybrid approach with metal foils
The EPFL team therefore took a different route. Instead of trying to join two types of powder in the same melt zone, the researchers investigated a hybrid method in which metal powder is combined with thin metal foils. ESA states that the project focused on three alloys of great practical importance: stainless steel 316L, the titanium alloy Ti-6Al-4V, and the aluminium alloy Al-12Si. The basic idea was that thin foils of the selected metal are laid, cut, and welded onto a substrate composed of previously consolidated powder or onto already welded foils, instead of two types of powder being intensively mixed with each other.
At first glance, such an approach may seem like a technical detail, but the consequences are significant. When the volume in which two metals react strongly chemically is reduced, the space in which brittle phases can form is also reduced. At the same time, the way heat is conducted through the joint changes, making it possible to control the local temperature field more precisely. ESA’s project description states that it is precisely the combination of powders and foils, together with the possibility of shaping the laser beam, that provides new degrees of freedom for producing very clean, high-resolution interfaces between materials. In other words, the goal is no longer only to join two metals, but to shape the boundary between them so that it is mechanically sustainable and microstructurally controlled.
What beam shaping means and why it matters for the material interface
One of the important elements of the project was reliance on earlier ESA work on laser beam shaping developed במסגרת the Off-Earth Manufacturing and Construction campaign. In standard metal 3D printing, the distribution of laser energy strongly affects melt depth, cooling rate, and microstructure development. If energy is distributed in a way that creates sharp thermal gradients, the danger of high residual stresses increases. Beam shaping allows finer control of heating, and therefore a more controlled transition between two materials that are otherwise difficult to join.
For industry, this is particularly important because the quality of the interface is determined not only by whether the joint “took”, but also by what its long-term mechanical response will be. In a component operating under thermal cycles, vibrations, or mechanical loads, a tiny crack at the material boundary can over time grow into a critical failure. ESA and EPFL therefore do not view this technology merely as a laboratory demonstration, but as an attempt to create a process in which heat paths, cooling, and chemical interaction are sufficiently controlled for the joint to remain stable after manufacturing as well.
The most important result: a crack-free interface in a particularly demanding combination
Among the results that attracted the most attention, the achievement of a crack-free joint between the Ti-6Al-4V and Al-12Si alloys stands out. This combination is a good test of the seriousness of the problem, because titanium and aluminium under such conditions readily bond into brittle intermetallic compounds, which in more conventional approaches often leads to delamination and cracking. According to a research summary published by the Paul Scherrer Institute at the end of December 2024, introducing a titanium foil resulted in a thinner intermetallic layer, lower residual stresses, and an interface without major cracks. The same source states that operando synchrotron X-ray diffraction and thermal numerical modelling showed how the foil changes the heat flow during the process, enables a kind of preheating, and reduces the thermal gradients that otherwise favour the formation of stresses.
This is an important message because it confirms that the problem of multi-material printing is not only in the chemistry of the materials, but also in the geometry and dynamics of the process. If heat can be guided differently through the joint, and the volume of the reaction zone reduced, then combinations that until yesterday were regarded as highly risky can become manufacturable. The scientific paper published in the journal Additive Manufacturing at the beginning of January 2025 further reinforced this finding and gave it visibility beyond ESA’s own development line.
Advantages that go beyond merely avoiding cracks
The benefits of the hybrid approach are not limited solely to the fact that the interface does not crack. EPFL and partner researchers point out that the use of foils can reduce the risk of powder contamination, which is important from both an economic and a process standpoint. In the conventional multi-powder approach, powder separation and reuse can become problematic, especially when expensive or reactive materials are involved. Foil as a secondary material reduces the need for intensive mixing of different powders in the processing zone, making it easier to preserve system cleanliness and process predictability.
In addition, this method of building makes it possible to achieve both sharp boundaries and gradual transitions in chemical composition, depending on what the design requires. This is exceptionally useful for parts that must combine different functions within the same piece. One segment can be optimised for strength and load-bearing capacity, another for thermal or electrical conductivity, and a third for corrosion resistance or operation in an aggressive environment. According to ESA and EPFL, it is precisely such combinations that sectors such as the space industry, energy, and biomedicine are seeking, where a component is increasingly expected to perform more than one dominant function.
Where the limitations arise when the technology is scaled up
Although the results show that the concept is technically viable, the project did not conceal serious limitations either. Scaling the process proved to be the next major obstacle. ESA’s summary states that as the printed area increases, it becomes increasingly difficult to ensure good contact between the foil and the substrate, while residual stresses accumulate as build height increases. The result can be bubbles, local lifting of layers, and delamination. In other words, what works on a smaller sample does not automatically have to work on a larger industrial part with complex geometry.
This is a common pattern in the development of advanced manufacturing technologies. Proof of concept must show that the physical principle is valid, but only the transition to larger dimensions and real working components reveals how robust the process is. In this case, the limiting factors are not only the choice of materials, but also the way heat “escapes” from the geometry, how the foil adheres to the substrate, and how precisely the welding of each new layer can be controlled. For this reason, the researchers stress that much better thermal management, as well as detailed process modelling, is necessary for serious industrial application.
The next step: a digital twin of the process
One of the most interesting messages of the project is that future development is not seen only through additional experiments, but also through the construction of a reliable digital twin of the hybrid powder-foil process. ESA’s project description and related research materials emphasise the need to expand the experimental database, including thermal camera analysis and numerical predictions. The idea of a digital twin is that the behaviour of the process can be simulated before manufacturing itself: how heat will spread, where the greatest stresses will arise, when the risk of unwanted phases forming is highest, and how to change parameters to avoid this.
For industry, this is not an academic luxury upgrade, but a key condition for moving from research success to reliable manufacturing. With expensive materials and complex parts, the number of trial-and-error attempts must be kept as low as possible. If a model can predict the behaviour of the joint well enough before printing, development is accelerated, waste is reduced, and the likelihood increases that the part will meet the required mechanical and functional properties already in the early iterations.
Why this matters for the space industry, but also for the broader market
The European Space Agency views this project in the context of a broader advanced manufacturing strategy. The Discovery programme, according to ESA’s official description, funds research, studies, and early stages of technological development aimed at new and potentially disruptive ideas. Through the Open Space Innovation Platform, or OSIP, such ideas can enter ESA’s innovation stream even when they come from academia or smaller research teams. In the case of the project led by EPFL, this is exactly such a trajectory: the idea entered through the open OSIP channel and was then supported through Discovery as a co-funded research project.
For the space industry, multi-material additive manufacturing has very concrete value. Spacecraft, satellites, propulsion assemblies, and auxiliary systems require strictly optimised parts in which low mass, high mechanical strength, resistance to thermal loads, and functional integration often have to be reconciled. If multiple functions can be combined in one piece, the number of joints is reduced, assembly is simplified, and room is created for lighter, more efficient, and more reliable systems. But the same principle also applies to medical implants, heat exchangers, energy components, and specialised industrial tools, where the local properties of materials often decisively determine the practical value of the product.
The bigger picture: from laboratory demonstration to a manufacturing tool
Caution in interpreting the results is still necessary. The available data show that this is a very promising step, but not a technology that is already ready to replace existing industrial processes on a large scale. What can now be stated is that the hybrid method with foils has shown clear potential for improving local microstructure and mechanical behaviour at interfaces between otherwise problematic materials. It has also been shown that better control of heat paths and beam shaping can play a decisive role in avoiding cracks. However, it is equally clear that the path to reliable serial application will require further experiments, more sophisticated models, and solving scaling problems.
This in no way diminishes the importance of what has been achieved. In the field of metal 3D printing, progress often does not come through a spectacular leap, but through removing one fundamental limitation after another. If the control of interfaces between different metals can indeed be raised to a new level, then space would open up for a new generation of components in which design would no longer be adapted to the limitations of a single material, but materials would be adapted to the function of a particular part of the component. That is precisely where the broader value of this work lies: not only in showing how to avoid a crack, but also in showing how to think differently about the very architecture of metal 3D printing.
Sources:- European Space Agency, Activities Portal – official project description “3D printing of multi-materials combining metallic powders with foils, and using beam shaping”, including objectives, selected alloys, and the technical concept of the hybrid LPBF approach.- European Space Agency, Discovery programme – official presentation of the Discovery programme, its place in ESA’s innovation cycle, and the types of activities it funds.- European Space Agency, OSIP – explanation of how the Open Space Innovation Platform works and its connection with the Discovery and Preparation programmes.- Paul Scherrer Institute – overview of research results on reducing cracks in multi-material printing by combining powder and metal foils, with emphasis on the Ti6Al4V–AlSi12 system.- Research Portal, Institut Polytechnique de Paris – bibliographic record of the paper “Avoiding cracks in multi-material printing by combining laser powder bed fusion with metallic foils: Application to Ti6Al4V-AlSi12 structures”, published on 5 January 2025.- EPFL Infoscience – record of a doctoral thesis on the manufacture of multi-material metal structures with engineered interlayers and microstructures in laser additive processes.- EPFL – profile of Professor Roland Logé with information on his field of work and relevant publications in additive manufacturing.
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