# Design and Assessment of an Austenitic Stainless Alloy for Laser Powder Bed Additive Manufacturing
## 3 Results
### Experimental Validation
#### 3.2.3 Mechanical Properties  
In its as-built condition, the average hardness of the alloy is of 216 \(\pm\) 6 HV10, which falls within the upper range of typical hardness values for wrought 316L, usually between 170 and 220 HV [65], and is close to the hardness of 316L produced by LPBF, which has been reported at 231 HV [73]. Tensile tests were conducted at room temperature along two distinct orientations, with the tensile axis aligned either parallel to the building direction (BD) or to the scanning direction (SD) to evaluate a potential anisotropic behavior. Three tests were performed for each orientation. The test results (Figure 9) exhibit good reproducibility, showing yield stress differences below 5 MPa between specimens for both SD and BD orientations. The material tested along SD exhibits the highest strength, with an average yield stress of 520 MPa, an ultimate tensile stress (UTS) of 600 MPa and an elongation to fracture of 40%. In contrast, the material tested along BD displays a yield stress 6% lower (490 MPa) and a UTS 14% lower (525 MPa). These differences may be due to the slight anisotropy of the cellular dendrite microstructure of the samples, as observed in [74], along with the fact that metallurgical defects are more easily introduced into the bonding area between two consecutive layers [75]. While stress-strain curves in horizontally cut samples are quite reproducible, vertically cut samples exhibit notable discrepancies in elongation to fracture, suggesting potential microstructure variations. The mechanical properties of the optimized alloy can be compared with the reference 316L alloy. For example, in the [PERSON] et al. work, a 316L produced by LPBF had a yield strength of 623 MPa, a UTS of 726 MPa, and an elongation of 47% [73]. Our optimized alloy offers a yield strength and UTS that are both 17% lower than 316L for the same elongation. Therefore, future development could focus on further increasing strength, for example by increasing the maximum allowable concentration of alloying elements during optimization. Figure 8: IPF map indicating the crystalline orientation along BD for (**a**) the cross-section of melt pools along SD direction, (**b**) the cross-section along BD and (**c**) pole figure of [100] planes. The fracture surfaces of the tensile specimens were observed by SEM (Figure 10(a)). In all samples, ductile fracture is observed, with microvoids and dimples characteristic of ductile fracture. However, occasional small spherical inclusions were noted, as illustrated in Figure 10 with a red arrow. The EDX analysis of these inclusions (Figure 10(b,c)) show the presence of Al and O, indicating that they are probably alumina. Interestingly, these inclusions were not initially detected through SEM imaging of the powder. As aluminum exhibits a significantly higher affinity for oxygen compared with other alloying elements, the presence of aluminum oxides may result from a small oxygen fraction within the powder or the atmosphere of the laser chamber. Consequently, these inclusions are likely due to contamination during the process. To mitigate their occurrence, a better control over powder processing and storage conditions, coupled with monitoring and regulating the oxygen content within the LPBF chamber, may prove effective in reducing the incidence of such inclusions. However, the latter are always a few \(\upmu\)m in diameter, so that, for the reasons already invoked, pores cannot be at the origin points of cracking under static or even cyclic loading. The challenge of powder oxidation could nevertheless be addressed in future alloy design research. The introduction of additional criteria may help to penalize elements that are particularly prone to oxidation. For example, one possible method could be to develop a penalty function based on the standard free enthalpies of formation of their respective oxides.