## 3 Results and Discussion  
### Microstructure Analysis of the SS308L and Inconel625  
According to the Ferrite-Austenite (FA) mode, the solidification process of 308L stainless steel can be described as follows: initially, primary \(\delta\)-ferrites form from the liquid phase L. As rapid cooling ensues, \(\gamma\)-uastenite phases begin to grow and gradually replace the primary ferrite. The SS308L region predominantly comprises austenite (FCC), with a small proportion of ferrite (BCC) present due to the residual \(\delta\)-ferrite. The microstructure in this region is primarily dendritic, with both equiaxed and columnar dendrites. As the height of the SS308L region increases, a deviation in the dendrite growth direction occurs. Figure 3: Pressure strategies for each experimental case. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**CASE**} & **SS 308L** & **Inconel 625** \\  & **(1–20 th Layer)** & **(21–40 th Layer)** \\ \hline
1 & Not applied & Not applied \\
2 & Not applied & 10,000 N \\
3 & 5000 N & 10,000 N \\
4 & 10,000 N & 10,000 N \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Pressure parameters of each experimental case. The microstructure of the SS308L:non-pressure, as shown in Figure 4a, exhibited the formation of columnar grains with a strong directional tendency towards the build direction. This characteristic could be attributed to the directional nature of cooling commonly observed in WAAM [19]. In the SS308L region, the microstructure was predominantly ferritic due to the relatively low carbon content of the filler wire. As shown in Figure 4, increasing loads led to both a further reduction in the directional tendency of the microstructure and a refinement of the grains. Figure 4d,e show the Inconel625 region. The observed microstructure was entirely austenitic, consistent with all the solid solution-strengthened Ni-base alloys [20]. Figure 4d,e show the microstructures of Inconel625:non-pressure and Inconel625:10,000 N, respectively. The predominant feature of the grain growth pattern in both samples was dendritic. Continuous columnar grains can be observed in Figure 4d, whereas Figure 4e reveals the presence of discontinuous dendrites. These characteristics were likely due to microstructural changes and thermal cycling occurring during the rolling process. The Scanning Electron Microscope (SEM) images, coupled with the corresponding data from the elemental mapping at the interface and on the SS308L and Inconel625 sides, are presented in Figure 5. A detailed representation of the elemental distribution is provided for individual elements. Among the alloy constituents, Chromium (Cr) alone demonstrated a uniform distribution throughout the interface, due to the near-identical weight proportions in both consumables (as shown in Table 1). In contrast, Nickel (Ni), Niobium (Nb), and Molybdenum (Mo) were predominantly concentrated on the Inconel625 side, while Iron (Fe) and, to a lesser extent, Manganese (Mn) were more abundant in SS308L. A trace of Fe diffusion was also discernible on the Inconel625 side, primarily adjacent to the interface. Figure 6 provides a visual representation of the EDS elemental mapping results traversing the interface region. In the process of the fusion welding of bimetallic alloys, the partially melted zone (PMZ) remains prone to the formation of liquidn cracks. In contrast, no such anomalies were spotted at the bi-metallic interface in our study. Increments in Nb and Mo on the Inconel 625 side were also noted. Moreover, Figure 6 shows the progressive compositional transition within the interfacial region, highlighting an absence of elemental segregation. Figure 4: Microstructures of the (**a**) SS308L:non-pressure, (**b**) SS308L:5000 N, (**c**) SS308L:10,000 N, (**d**) Inconel625:non-pressure, and (**e**) Inconel625:10,000 N.  
The SEM micrograph in Figure 7 reveals the existence of precipitates interspersed within the Inconel 625 layer.