Ultrasonic additive manufacturing of nanocrystalline laminated composites

Austin A Ward,Hans-Henrik König,Donovan N Leonard,Zachary C Cordero,Greta Lindwall

doi:10.1557/s43578-021-00462-5

Abstract

Ultrasonic additive manufacturing has been used to fabricate laminated composites of commercially pure aluminum and a nanocrystalline nickel–cobalt (nc-NiCo) alloy. The nc-NiCo alloy would not weld to itself but readily welded to aluminum. Thus, by alternating between foils of nc-NiCo and Al, we achieved multi-material laminates with strong interlayer bonding. Electron microscopy showed that the nanoscale grain structure of the nc-NiCo was preserved during deposition and that the nc-NiCo/Al weld interface was decorated with comminuted surface oxides as well as Al–Ni–Co intermetallics. These findings are considered in light of process models of junction growth, interdiffusion, and grain growth, which together reveal how the different pressure- and temperature dependences of these phenomena give rise to a range of processing conditions that maximize bonding while minimizing coarsening and intermetallic formation. This analysis quantitatively demonstrates that using a soft, low melting point interlayer material decouples junction growth at the weld interface from grain growth in the nc-NiCo, expanding the range of optimal processing conditions.Graphical abstract

Highlights

Ultrasonic additive manufacturing (UAM) is a hybrid additive manufacturing technique that uses ultrasonic welding to deposit foil feedstock, CNC machining to selectively remove excess material
While several investigators have claimed that there is anomalously fast interdiffusion during ultrasonic welding and have attributed this effect to exotic physics, we recently showed that the extent of interdiffusion can be estimated accurately by combining the temperature field at the weld interface and the standard form of Fick’s second law
The Al adjacent to the weld interface was nanostructured and contained a dispersion of nano-oxides, indicating that the soft, oxide-covered Al surface asperities experienced severe plastic deformation as they flattened against the harder, smoother nc-NiCo surface

Summary

Introduction

Ultrasonic additive manufacturing (UAM) is a hybrid additive manufacturing technique that uses ultrasonic welding to deposit foil feedstock, CNC machining to selectively remove excess material. A cylindrical sonotrode rolls across the build envelope while it compresses the feedstock and vibrates transverse to its travel direction. The mechanical action of the sonotrode disrupts oxides and plastically deforms surface asperities at the weld interface, facilitating junction growth and metallurgical bonding [1]. Asperity deformation underneath the rolling sonotrode is promoted by frictional heating at the weld interface, which results in homologous temperatures in the range 0.4–0.8 [2]. The thermal excursion during UAM is brief, making it an attractive approach for fabricating net-shaped components from thermally unstable materials [2,3,4]. UAM has successfully densified Ni-base and Fe-base metallic glasses without disturbing their amorphous structure [5,6,7]

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Conclusion