## 3 Results and Discussion
### Novel Materials for Improved Structural Safety  
In Section 3.1 we demonstrated that processing defects, such as pores, may act as notches in critical design regions and thus act as preferred sites of crack initiation. Consequently, if a larger number of pores (i.e., crack starters) in additively manufactured components was present, materials of lower crack propagation rate would be required to at least maintain sufficient component lifetime and safe operation such as that known from conventionally manufactured materials. Materials tailored for additive manufacturing processes would enable an additional improvement of component lifetime, safety, and cost savings. Of course, safety also depends on the maintenance and management of the structure, but here too, material development can contribute to increasing safety. Application of more robust materials increases the margins of inherently safe operation. The approach is not to minimize pores, but to develop a material with active crack obstruction mechanisms, which inhibit--or at least retard--both crack initiation and crack propagation. Two main mechanisms can be utilized to accomplish this. First is the option of taking advantage of in situ heat treatment by the so-called \"temper bead effect\" [26; 27; 28; 29] during the AM process. The component will then benefit from potential time and cost savings over conventionally produced components. Rapid precipitation kinetics are the essential prerequisite to accomplish this. For this reason, the novel, stainless High Performance Ferritic (HiperFer) steel, developed at Forschungszentrum Juelich GmbH, is a high potential candidate. Strengthening of these steel grades is achieved by a combination of solid solution and intermetallic (Fe,Cr,Si)\({}_{2}\)(Nb,W) Laves phase particle precipitation [30]. The microstructural and mechanical properties of HiperFer steels are described in detail in [31]. In the current paper, HiperFer-like steel was evaluated on the basis of its in situ heat treatment capability in laser metal deposition (LMD) processing. The second mechanism is to take advantage of \"dynamic strengthening\" under cyclic loading at high temperatures to actively obstruct crack initiation and propagation and thus enhance component lifetime and safety. In HiperFer, this can achieved by thermomechanically induced precipitation [17] of the Laves phase under cyclic loading, or more generally speaking, under (cyclic) plastic deformation at temperatures above 600 \({}^{\circ}\)C [18]. Figure 18 illustrates a comparison of thermomechanical fatigue curves (100% out-of-phase TMF experiments, i.e. \(\Delta\epsilon_{\text{mech.}}=-\Delta\epsilon_{\text{th. }}\), meaning that thermal expansion is fully obstructed by the testing machine during cycling through the temperature range of 50 to 650 \({}^{\circ}\)C) of 316L, Crofer22 H, and HiperFer 17 Cr2. Crofer22 H is a predecessor of HiperFer 17 Cr2 and was developed at Forschungszentrum Juelich GmbH for application in high temperature solid oxide fuel cell interconnectors. Crofer22 H cyclically hardens during the initial  
Figure 17: (**a**) Traces of elemental segregation and (**b**) corresponding EDX mappings. approximate 30 cycles (\(\approx\)1% of technical lifetime) of fatigue testing by thermomechanically induced precipitation of Laves phase particles, preferentially at dislocations induced by cyclic plasticization. The end of the hardening range corresponds to the maximum of the fatigue curve (cf. \"N\({}_{\text{h}}\)\", Crofer22 H curve in Figure 18). The technical lifetime was evaluated from the intersection of linear approximations to the \"stable\" and the \"damage\" curve sections of the TMF curves (cf. \"N\({}_{\text{f}}\)\", Crofer22 H curve in Figure 18). The beginning of the damage range was evaluated by deviation of the fatigue curve from a linear approximation to the stable curve section (cf. \"N\({}_{\text{d}}\)\", Crofer22 H curve in Figure 18).