Mitigating Cracks in Multi-Material Printing

Laser powder bed fusion (LPBF) is a versatile additive manufacturing technology capable of producing multi-material metallic structures. However, when using two different metallic powders, significant challenges arise, including powder contamination, limited powder reusability, and the formation of interfacial defects like brittle intermetallic compounds (IMCs). These issues can compromise the mechanical integrity and functionality of multi-material components, particularly in demanding applications like aerospace.

Our study demonstrates the advantages of combining metallic powders with thin foils, rather than relying solely on powders, to address these challenges. Using Ti6Al4V and AlSi12—two materials of high industrial relevance—we explored how this hybrid approach influences interfacial behavior. Traditional powder-based LPBF often leads to delamination and cracks at the interface due to the formation of brittle IMCs like Al₃Ti. By introducing a titanium foil, we observed significant improvements: a thinner IMC layer, a reduction in residual stresses, and a crack-free interface.

The effectiveness of this approach was confirmed through detailed experiments and advanced simulations. Operando synchrotron X-ray diffraction (XRD) performed at the Materials Science beam line of the Swiss Light Source provided insights into the stepwise evolution of IMCs, showing a transition from Al-rich to Ti-rich phases. Thermal finite element modeling (FEM) revealed how the foil alters the heat flow during printing, enabling preheating of the foil and reducing thermal gradients. These changes create a more favorable thermal regime, minimizing residual stresses across the interface. Nanoindentation further confirmed a significant reduction in stress levels, correlating with the absence of large cracks.

This hybrid approach also prevents powder contamination, improving the reusability of metallic powders—a key benefit for sustainable and cost-effective manufacturing. The process was found to be not only effective for Ti6Al4V and AlSi12 but also potentially applicable to other challenging material combinations, broadening its industrial relevance.

Looking ahead, this study opens new avenues for innovation in multi-material LPBF. Future investigations could explore the effects of depositing multiple foils, layering powders over foils, or introducing an interlayer foil made of a third material to mediate between two dissimilar alloys. These approaches may further enhance interfacial quality, reduce residual stresses, and allow for better control of IMC formation.

In summary, using metallic foils as a complementary feedstock in LPBF represents a promising solution to longstanding challenges in multi-material additive manufacturing, offering improved structural integrity and reliability across a wide range of applications.