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The deformation behavior of particles plays a significant role in achieving adhesion during cold spray. The deformation behavior of the particles is associated with the fracture of the oxide layer and recrystallization, which are the key elements of the quality of cold spray. Studies of particle compression have been made to understand the deformation behavior of a particle. However, the deformation behavior of particle under controlled load and precise and high strain rate is yet to be studied. Here, we show the oxide layer fracture pattern and recrystallization regime under controlled load with a precise and high strain rate. We found that the cracks in the oxide layer initially appeared on the equator of the particle and propagated towards the edge of the top surface. Meanwhile, on the top surface, the circumferential crack was developed. On the other hand, the nanoindentation result showed that the compressed particle under a high strain rate has an unusual load-displacement behavior. Our results demonstrate that the oxide layer fracture behavior corresponds to the adhesion mechanism suggested by previous studies. Our study also revealed that recrystallization takes place within the particle under a high strain rate. We anticipate this finding to give a general insight into the deformation behavior of particles during cold spray. For instance, since the recrystallization behavior at a given strain rate can be predicted through this study, the resultant grain size and shape, which is associated with mechanical properties, can also be predicted. Furthermore, the amount of strain and strain rate to form optimal adhesion can be evaluated.
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Surface oxide layer strengthening and fracture during flattening of powder particles
Surface oxide layer fracture and the subsequent exposure of clean metallic surfaces are critical in various solid-state processes for powder consolidation and additive manufacturing. We resolve this process in-situ by deforming individual spherical powder particles inside a scanning electron microscope. We reveal three fracture modalities, i.e., meridian, radial, and circumferential cracking that sequentially activate with particle flattening. Real time measurements of load and displacement upon particle flattening also reveal a significant strengthening effect by surface oxide. We attribute the strengthening to two mechanisms: the composite strengthening and the strain gradient strengthening.
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- Award ID(s):
- 2145326
- PAR ID:
- 10497724
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Scripta Materialia
- Volume:
- 244
- ISSN:
- 1359-6462
- Page Range / eLocation ID:
- 116008
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.scriptamat.2024.116008
