## 5 Conclusions  
In the presented work, the damage tolerance of 22 wt.% Cr, fully ferritic stainless steel Crofer(r) 22 H, as well as advanced ferritic-martensitic (AFM) steel P91, was analyzed using the short-time procedure \(\mathrm{PhyBaL}_{\mathrm{CHT}}\). This was based on instrumented cyclic indentation tests (CITs), which were performed  
Figure 8: Sub-grain formation in ferritic Crofer®22 H, observed in the specimen, failed after 4342 TMF-cycles [5].  
Figure 7: Cyclic hardening exponent\({}_{\mathrm{CHT}}\)\(|\)e\({}_{\mathrm{II}}\)\(|\) and martens hardness _HM_ at the volume of the gauge length, crack edges and plastic zone in front of the crack tip at a fatigue crack observed at a Crofer®22 H specimen loaded for 4342 TMF-cycles.  
at specimens and loaded for the different numbers of oop TMF-cycles, as well as in the vicinity of a fatigue crack in a Crofer(r)22 H specimen. Consequently, the presented work focuses on the evolution of damage tolerance during TMF-loading, as well as the local changes in defect tolerance in the vicinity of a fatigue crack. The following conclusions can be drawn from the results obtained:  
* In the initial state, Crofer(r)22 H has a higher damage tolerance compared to P91, which correlates to higher TMF-lifetime;
* After approximately half of TMF-lifetime, an increase of damage tolerance can be observed for Crofer(r)22 H, which is not seen for P91 and correlates with changes of the Laves phase particle size and distribution;
* Polygonization, resulting from degradation of martensite lath structure in P91, does not influence the microhardness, as well as cyclic hardening potential obtained in CITs;
* For Crofer(r)22 H, the changes in damage tolerance correlate well with the cyclic deformation behavior observed in TMF-experiment and the accompanied microstructural changes;
* The cyclic hardening potential, and hence, damage tolerance, as well as hardness, is different between the crack tip and crack edges in Crofer(r)22 H;
* CITs are a powerful means to analyze the TMF-induced changes in mechanical properties, i.e., cyclic hardening potential, as well as for the investigation of locally restricted changes in the material's cyclic deformation behavior.  
However, the presented work also shows that a thorough understanding between the microstructural changes (Laves phase particle evolution, dislocation density, and sub-grain boundary formation) and the resulting deformation behavior observed in CITs is a prerequisite. This will be considered in further investigations.  
Conceptualization, B.B., D.G., T.F., B.K. and T.B.; methodology, B.B., D.G., T.F., B.K. and T.B.; investigation, D.G. and T.F.; writing--original draft preparation, B.B., D.G. and T.F.; writing--review and editing, B.B., B.K. and T.B.; visualization, D.G.; supervision, B.B., B.K. and T.B.; project administration, B.K. and T.B.; funding acquisition, B.K. and T.B. All authors have read and agreed to the published version of the manuscript.  
The financial support of the priority research activity of Rhineland Palatinate \"Advanced Materials Engineering (AME)\" is gratefully acknowledged.  
The authors would like to acknowledge the support of [PERSON] and [PERSON] in mechanical testing as well as [PERSON] for metallographic preparation and [PERSON] and [PERSON] for microstructural characterization work.  
The authors declare no conflict of interest.