During the past decade, synchrotron X-ray and neutron techniques have emerged as powerful tools for studying the microstructure of additively manufactured (AM) materials. In post-built samples, they enable the detection of defects such as cracks and pores, the identification of crystallographic phases, and the determination of dislocation densities [1-3]. Their true strength, however, is revealed when applied operando during AM. Real-time measurements capture the microstructural changes occurring within and around the melt pool, providing direct insight into phase transitions, thermal effects, and stress evolution—factors that ultimately dictate the performance of AM components.

Fusion-based AM of dissimilar metals remains particularly challenging, as large differences in thermophysical properties and solidification behavior often lead to chemical inhomogeneities and interfacial cracking. Using operando synchrotron X-ray diffraction and imaging, we investigate both laser powder bed fusion (LPBF) and direct energy deposition (DED) of various multi-material systems, such as copper-steel, copper–nickel, copper-nickel, tungsten-steel [4-6]. Real-time diagnostics reveal distinct cracking mechanisms—including solidification cracking, liquation cracking, and metal-induced embrittlement—as well as stochastic material transport events that govern interfacial homogenization. Complementary studies of stainless steels combined with tungsten further show how alloy composition, solidification velocity, and cooling rate dictate the formation and retention of BCC and FCC phases.

Together, these results establish a mechanistic understanding of how microstructural evolution in multimaterial systems is governed by both local thermal conditions and intrinsic alloy properties. Such insights are essential for refining predictive models and guiding the design of more reliable multimaterial architectures in AM.

[1] J. Su, L. Chen, S. Van Petegem, F. Jiang, Q. Li, J. Luan, S.L. Sing, C. Tan; Materials Today, 2025, 88, 240.

[2] D. Mani, P. Cloetens, D. Karpov, F. Monaco, B. Chehab, R. Shahani, S. Van Petegem, P. Barriobero-Vila, K. Bugelnig, G. Requen; Materials Characterization, 2025, 225, 115109.

[3] S. Gaudez, F. Malamud, W.A. Hearn, S. Sumarli, M. Strobl, S. Van Petegem; Materials & Design, 2025, 251, 113658.

[4] A. Özsoy, W.A. Hearn, S. Gaudez, R. Jeswani, Y. Chen, A. Rack, Z. Hegedüs, N. Casati, R.E. Logé, S. Van Petegem; Virtual and Physical Prototyping, 2025, 20, e2526798.

[5] A. Özsoy, S. Gaudez, W.A. Hearn, A. Baganis, Z. Hegedüs, Y. Chen, A. Rack, S. Van Petegem; Additive Manufacturing, 2025, 110, 104950.

[6] N. Garrivier, S. Van Petegem, M. Strobl, M. Pouchon, E. Tosoratti, A. Cretton, K.V. Falch, D. Ferreira Sanchez, M. Makowska; in review

Dr. Steven Van Petegem