## 2 Microstructure
All of the experiments conducted in different studies proved that the size of dendrite arms would be in the range of a few microns. For example, [PERSON] et al. found that the average PCAS of AISI 316L produced via DED increased from 3 to 9 \(\upmu\)m when the laser power increases [42]. Table 2 compares all the dendrite sizes that have been found in different studies. It should be highlighted that the evaluation of PCAS has been carried out using SEM images and three-angle method [37; 49; 64]. In addition to the effect of cooling rate on microstructural morphology, it should be noted that this rapid solidification process also results in the phase composition of the microstructure of the samples in the as-built condition. In general, in the standard rapid solidified austenitic stainless steel, two distinct microstructural constituents can be achieved: austenite (\(\upgamma\)) and \(\delta\)-ferrite [68]. However, in order to predict the microstructure of the material from the phase composition point of view, some chemical composition-based phase diagrams, such as Schaffler and DeLong diagrams, are employed. The Schaffler diagram is the most accepted diagram used to predict the final microstructure of the material. In fact, this diagram is commonly employed to estimate the \(\delta\)-ferrite content in the final microstructure of AISI 316L (Figure 9a). In addition to predicting \(\delta\)-ferrite content, this diagram is also capable of predicting the existence of ferrite, martensite, and austenite phases in AISI 316L alloy as a function of the Cr and Ni equivalents [69]. However, it is reported that this diagram is not an exact diagram and, thus, the outcome is an approximation of the final \(\delta\)-ferrite content [69]. [PERSON] et al. also studied the solidification mode of the AISI 316L alloy according to the role of alloying elements [41]. In their work, it is shown that by changing the ferrite stabilizer or austenite stabilizer content the solidification mode is different and, consequently, the final alloy can be either duplex or fully austenitic (Figure 9b). However, it should be noted that this diagram has typically been used to predict the microstructure of corrosion-resistant steels with carbon content up to 0.25% after the welding process. Since the cooling rate is always higher than the welding process in the DED process, the solidification is not under equilibrium conditions. Therefore, it is highly recommended that, in addition to the conventional \begin{table}
\begin{tabular}{c c c} \hline \hline
**Author** & **Dimension (\(\upmu\)m)** & **Ref.** \\ \hline [PERSON] et al. & 2.8–4.8 & [37] \\ [PERSON] et al. & 1.3–3.0 & [65] \\ [PERSON] et al. & 3.25–8.68 & [42] \\ [PERSON] et al. & \textless{}5 & [66] \\ [PERSON] et al. & 8–20 & [51] \\ [PERSON] et al. & 2–15 & [67] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: A summary of PCAS reported for AISI 316L alloy processed by DED. Figure 9: (**a**) [PERSON]’s diagram and (**b**) austenitic steel solidification diagram [41]. Schaffler diagram, another diagram, namely the pseudo-binary predictive phase diagram, is used [70]. This means that once the theoretical \(\delta\)-ferrite content is defined by Schaffler diagram, the WRC-1992 modified Cr and Ni equivalent formulas, which are shown on the X- and Y-axes of Figure 10a, can be used to place the steel being investigated in the pseudo-binary phase diagram (Figure 10). For instance, [PERSON] et al. studied the microstructure of AISI 316L produced by DED. At first, they found that according to the chemical composition of the material and the Schaffler diagram, the estimated \(\delta\)-ferrite content of the columnar boundary lies in the region of 20% \(\delta\)-ferrite.