PSI - Issue 38

Christophe Grosjean et al. / Procedia Structural Integrity 38 (2022) 94–108 C.Grosjean and al. / Structural Integrity Procedia 00 (2021) 000 – 000

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4

a

b

c

Fig. 2. (a) Part produced by L-PBF on the plate. Supports and plate have not been yet removed. (b) metallography exam on a vertical section without etching for porosity characterisation and (c) after etching for microstructure characterisation.

Table 1 : Mechanical properties of 17-4PH produced by L-PBF on an EOS M290 machine with a layer thickness of 40µm after a heat treatment (Annealing 1030°C 1h + ageing 480°C 2h). Average over 3 samples.

R m [MPa] R p0.2 [MPa] A%

Z% E [GPa]

Horizontal 1352

1226 1238

12,5 42 12,5 45

187 195

Vertical

1358

The plate and supports were mechanically removed and then sandblasted on the outer surfaces to improve the appearance. Tensile tests (see Table 1) and micrographic examination were performed on separate samples. Very little porosity <0.1% is measured (Fig. 2(b)). The microstructure is martensitic (Fig. 2(c)). The anisotropy is very reduced. These results are similar to the EOS datasheet for this material [4]. L-PBF is the process that was selected for further testing (pressure drop and fatigue) because of its maturity and its ability to produce complex shapes compatible with many hydraulic components. 4.2. MBJ production and characterization The MBJ technology requires a sintering step during which a dimensional shrinkage of about 20% occurs in each of the three directions. This requires anticipating this deformation in the initial printed geometry. In this case, the parts were made by ExOne as a subcontractor. This part is difficult to produce because of its large size for this process and its overall shape with two heavy areas connected by a relatively thin channel. The respect of the geometry is a big challenge for such a part. For this first try, the global length was about one millimeter longer than expected, a global deformation (see Fig. 3(a)) and the circularity of the channel was quite bad (see Fig. 3(b)) . Those deformations appear during sintering due to the weight and friction in the furnace. Further work would be needed to optimize the geometry, for example by using dedicated supports during sintering. MBJ supports are separate elements produced from the same material and sintered simultaneously. Thanks to a non-sticking ceramic layer on the interfaces, they can be easily removed manually.