## 4 Conclusions  
As one of the most employed AM technologies, DED offers excellent potential for the production of complex shape components, which are arduous to produce through conventional processes. AISI 316L is a well-known austenitic stainless with high corrosion resistance, as well as good mechanical properties, which make this alloy an excellent candidate for several sectors, such as the automotive and petrochemical industries. This review article summarizes the latest research carried out to evaluate microstructures and mechanical properties of AISI 316L stainless steel processed by DED. The correlation between the DED process parameters, thermal history, and microstructure of AISI 316L materials is discussed in detail. It is found that most previous works have aimed to determine the optimal process parameters for the DED production of AISI 316L components. These efforts have been taken in order to improve the density and mechanical properties of AISI 316L components produced via the DED process through the control of their microstructure. However, it should be highlighted that, in spite of this research effort, a number of challenges remain that should be considered and addressed in further investigations. The main challenges are associated with the correlation among DED process parameters, thermal history, microstructure, and mechanical characteristics of the DED AISI 316L parts. To date, investigations of DED AISI 316L materials have demonstrated that:  
* Optimization of process parameters is a vital step that should be carried out carefully in order to achieve defect-free components with desired final characteristics. * DED process parameters markedly affect the cooling rate, thermal gradient and, accordingly, thermal history and porosity content of the parts. It is well known that the quality of DED parts is chiefly determined by the process parameters, as well as the starting powder (particle size and chemical composition). * Regarding the process parameters, the most important are laser power, scan speed, powder feed rate, building atmosphere, and deposition pattern. All these parameters influence the microstructure. The very high cooling rates of DED processes, with values around 10\({}^{3}\)-10\({}^{4}\) \({}^{\circ}\)C/s, involve the formation of columnar and cellular structures based on the direction of thermal flux. It was reported that the columnar structures are dominant throughout the specimens, while the cellular structures are predominant in the last deposited layers. * It is found that, the finer the PCAS, the higher the cooling rates. The high cooling rates generate very fine dendritic structures, as well as high dislocation densities, resulting in higher mechanical strength. * The microstructure is composed of austenite \(\gamma\) and \(\delta\)-ferrite, which is typically formed with the sub-grain structures enriched in Cr and Mo (\(\delta\)-ferrite stabilize elements). * Oxide formation is an undesired feature that affects the production of AISI 316L by the DED process. It is found that the presence of oxides can negatively affect the mechanical properties, even though an inert gas atmosphere is employed. * The aforementioned microstructure features lead to materials with higher strength and lower ductility values with respect to conventionally processed AISI 316L stainless steel. * Anisotropy in the tensile properties of DED components is widely detected; typically, the specimens produced along a direction parallel to the building platform present higher YS and US than specimens built perpendicular to the building platform. This can be attributed to different microstructure and thermal history, although there is a lack of extensive studies. * Grain morphology, texture, elongated dendrites, and lack of fusion defects are found to be the main factors associated with the perpendicular building direction that have an effect on the tensile properties of DED AISI 316L components.