# Study of the Direct Metal Deposition of AA2024 by ElectroSpark for Coating and Reparation Scopes
## 3 Results and Discussion
### Microstructure
Particularly, the layer-layer interfaces microstructure exhibits either equiaxed dendrites (highlighted in Figure 8a) or undefined dendrites morphology (highlighted in Figure 8b). Moreover, the different layers can exhibit the same cellular dendritic microstructure (highlighted by the circles A and B in Figure 8c) or different microstructures (highlighted by the circles C and D in Figure 8a). Moreover, inside of the same layer, both a dendritic morphology (circle E in Figure 8b) and a uniform distribution of fine second phase particles (circle F, Figure 8b) can be observed. The cellular dendrites, usually, grow anti-parallel to the main heat flux direction (perpendicular to layer-layer interface). As mentioned before, the scale of microstructure is variable, and the dendrites size is coarser in such a zone and finer in some others (compare circles A, B in Figure 8c and circle E in Figure 8b). The sizes and type of microstructure can be attributed to the different solidification condition induced by the manual process of deposition. Anyway, the scale of microstructure is in general quite fine due to the high cooling rate of the melt induced by the ESD process. Figure 6: Overview of longitudinal-section of the deposit: (**a**) longitudinal-section morphology of ESD layer from top view showing sequence of deposition of ESD splats in the same plane of view (the arrow indicates the interface formed between the splat); (**b,c**) SEM images showing different zone with fine microstructure and splat-splat interface. Figure 7: Overview of deposit cross-section: (**a**) Optical Microscope (OM) Nikon Epiphot image showing the microstructural of built-up layered deposit and (**b**) SEM micrograph showing the boundary of slender columnar like grain vertical to the build direction. Figure 9 shows the microstructure near the interfacial region in electrospray deposit. There is a thick interfacial region of about 20 \(\upmu\)m between the substrate and the deposit that can be observed (Figure 9a,b). Backscattered electron images reveal that this interfacial region is characterized by large constituent intermetallic particles that are distorted and partially melted surrounded by a high segregation (Figure 9a,b). By EDS analysis (Figure 9c) it was found that those deformed particles are the (Mn,Fe)\({}_{3}\)SiAl\({}_{12}\) phases coming from the substrate material because of melting and mechanical  
Figure 8: High magnification SEM images of the deposit cross-section showing some different areas inside the deposit. Yellow arrows indicate the microstructure in the layer-layer interfaces. (**a**) circles C and D highlighted the different microstructures in the different layers; (**b**) circle E shows dendrites with mixed morphology while the circle F shows uniform distribution of fine second phase particles inside the same layer; (**c**) circles A and B highlight the same cellular dendritic microstructure in different layers. Figure 9: (**a**) SEM micrograph showing the interface layer between deposit and substrate alloy (**b**) SEM micrograph (backscattering mode) showing the microstructure of deposit/substrate interface and (**c**) energy dispersive spectrometry (EDS) map to interface layer. mixing of both electrode and base material [25; 36]. The base material next to the interface does not present any chemical and microstructural modification or HAZ.