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Laser powder bed fusion is widely used for tooling applications, such as mould insert: conformal cooling channels are designed to decrease cycling time and homogenize the cooling rate. The Achilles' heel of additive manufacturing mould is the cooling channels close to the surface which generate high stress concentration and are not machined; as a result, they create weaknesses in the part and are likely to reduce the lifespan of the mould. It is necessary to study the impact of such channels on properties (fatigue, residual stresses, microstructure) and determine optimized laser strategies to reduce porosity that may occur near a contour. Residual stresses were first estimated above an internal channel after different heat treatments, and fatigue specimens were printed with a 3-mm diameter channel on an EOS M270 printer using different strategies such as several contours with a concentric offset. The impact of these strategies on fatigue properties was analysed through microstructural observations. Here, it was found that a double contour with an offset improved the fatigue life of the part by more than 10 times compared to the standard single contour strategy. [ABSTRACT FROM AUTHOR]

Materials produced by additive manufacturing (AM) often have different microstructures from those obtained using conventional metallurgy (CM), which can have significant impacts on the materials' durability, and in particular, resistance to corrosion. In this study, we were concerned with the susceptibility to pitting and environmentally assisted cracking (EAC) of 17-4PH martensitic stainless steel (MSS). We focused on the evolution from pitting to EAC, and the behaviour of MSS produced by AM was compared with that of its CM counterpart. Potentiodynamic polarisation tests were combined with chronoamperometry measurements performed without and with mechanical loading to study both stable and metastable pitting and the influence of stress on these processes. EAC tests were carried out and combined with observations of fracture surfaces. MSS produced by AM was more resistant to pit initiation due to fewer and finer NbC particles. However, the propagation kinetics of stable pits were higher for this MSS due to a higher amount of reversed austenite. The stress was found to stabilise the metastable pits and to accelerate the propagation of stable pits, which resulted in an increased susceptibility to EAC of the MSS produced by AM. These results clearly highlighted the fact that the reversed austenite amount has to be perfectly controlled in AM processes. [ABSTRACT FROM AUTHOR]