Processing of a steel-to-copper multimaterial through build-plate preheating and ultrasonic-assisted laser-based directed energy deposition

Additive manufacturing, and specifically laser-based directed energy deposition (DED-LB), represents one of the most versatile techniques for the fabrication of functionally graded materials due to its capability to achieve precise spatial control in the deposition of multiple feedstock materials. Nonetheless, the pronounced differences in the physical, chemical, and thermomechanical properties of coexisting liquid phases in the melt pool continue to pose significant challenges to process stability and defect mitigation. This study examines the influence of DED-LB process parameters on the interfacial bonding characteristics within a compositional gradient between AISI 316L stainless steel and CuCr1Zr alloy. Build-plate preheating was employed as an effective strategy to suppress crack formation by reducing thermal gradients and alleviating residual stresses. Additionally, the effect of ultrasonic excitation on the melt pool was investigated. The introduction of ultrasound promoted finer and more homogeneously distributed phases; however, it simultaneously induced pronounced perturbations in the melt pool, which compromised process stability. Optimized process parameters for the fabrication of thin-wall components with compositional gradients are reported, enabling the production of crack-free samples with minimized porosity and absence of lack-of-fusion defects. The resulting gradients were systematically characterized with respect to elemental composition and Vickers hardness, demonstrating close conformity to the designed compositional profile.