PSI - Issue 41

Saveria Spiller et al. / Procedia Structural Integrity 41 (2022) 158–174 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000–000

170

13

and expensive. MEAM is usually compared to Metal Injection Molding (MIM) since the post process of both techniques involved the same steps, debinding, and sintering. The main benefit of MEAM compared to MIM is that no molds are required. In several studies, the static mechanical properties of MEAM parts are compared to the ones obtained with other techniques, in particular MIM, SLM, and standard wrought materials. In this section, some examples are presented. The two main conclusions which are possible to draw are the following: the residual porosity of MEAM parts is usually higher compared to their counterparts, and this has a reflection on the strength properties, UTS, yield stress, or bending strength. Nevertheless, the ductility of the parts was proven to be high, sometimes higher than their counterparts. For example, Gong et al. (2019) compared the mechanical performances of 316L parts obtained with FDM and SLM with the mechanical properties of a standard AISI 316L. The comparison is represented in the bar plot below (Fig. 13).

Fig. 13. Comparison proposed by Gong et al. (2019)

Similar data were collected by Liu et al. (2020). According to both works, the difference in the mechanical proprieties is related to two main effects. The first is the residual porosity, which is quite high in a MEAM part if the process parameters and the deposition strategy are not well designed. The second effect is microstructural. The microstructure of the MEAM part presents equiaxed isotropic grains, without dislocations. This is the typical condition of annealed stainless steel, which leads to low yielding stress, UTS, and hardness. On the contrary, the strain at break is reduced by the porosity in the part. The same reasons are pointed out by Thompson et al. (2019), where the 316L parts undergo bending tests. In several other studies, MEAM parts are also compared with MIM parts (Caminero et al. (2021; Damon et al. (2019); Sadaf et al. (2021); Tosto et al. (2021)). When low residual porosity and high densification are achieved by MEAM parts, the mechanical properties are comparable to the ones of MIM parts, in terms of yiels stress, UTS, and elongation at break as well. This similarity is accentuated by the similar post-process which MIM and MEAM parts undergo, which results in a similar annealed microstructure. Safka et al. (2020) carried out a similar comparison with even more techniques: MEAM parts were debound and sintered with three different facilities. The SLM parts were tested as-printed and after milling, to improve the surface quality. Finally rolled sheet material was cut both with laser and water jet to obtain the conventionally manufactured specimens. Again, because of the coarser microstructure, the MEAM specimens showed lower strength but higher ductility and elongation at break. It is also interesting to notice how the MEAM parts differ when changing the post process condition. This means that the overall process is extremely sensitive to the facilities and the equipment and procedure used to carry out the post process. For what concerns the hardness, similar results and considerations can be observed regarding the dislocations, the annealed microstructure, and the resulting deformability of the specimens. For example, considering 316L parts, Liu et al. (2020) measured 145HV micro Vickers hardness, compared to 155 and 232 respectively AISI and SLM. Sadaf et al. (2021) also measured the Vickers microhardness, which value was found to be 285.5 HV, in agreement with average values found for MIM parts, between 250 and 290 HV. Gong et al. (2019) measured the Rockwell harness