Composite materials represent a fascinating class of materials, as new properties can be achieved by combining different phases. Challenging composite materials based on high-alloy austenitic stainless steels and zirconia are being researched at the Technische Universität Bergakademie Freiberg, Germany, within a major research programme. In Collaborative Research Centre 799, which has been funded by the German Research Foundation (Deutsche Forschungsgemeinschaft DFG) since 2008, new manufacturing methods are being explored, new steel compositions are being developed, microstructures and properties are being analysed and new approaches to material modelling are being established. For further information, readers are referred to the website tu-freiberg.de/forschung/sfb799. The fascination of the new composite materials results from the ability of both phases to martensitic phase transformations. Depending on the chemical composition and temperature, the steels used as matrix for the composites show either the transformation of the fcc structure into the bcc α′-martensite and thus the TRIP effect (Transformation-Induced Plasticity), or a deformation-induced twin formation (TWIP effect). The MgO partially stabilized zirconia used also exhibits a martensitic phase transformation from the tetragonal phase to the monoclinic structure. Thus, the two phases can interact in a complex way during mechanical loading. In the following articles, current research results are presented. They range from material production and the design of the steels to the analysis of the deformation mechanisms. First, the production of N-alloyed steel powders by inert gas atomization is treated (Korobeinikov et al.). Furthermore, the powder metallurgical production of composite materials via sintering (Baumgart et al.), spark plasma sintering (Radajewski et al.) and the production of composite beads via a slurry-based process (Oppelt et al.) are discussed. In further contributions, the hot forming of N-alloyed austenitic steels (Nam et al.) and the formation and dissolution of carbides in Al alloyed steels are investigated (Mola et al.). An insight into the deformation mechanisms is provided by in situ synchrotron diffraction (Ullrich et al.) and nanoindentation (Lehnert et al.). An important question for the martensitic phase transformation of the steel is the thermodynamic driving force for the γ-α′ phase transformation (Hauser et al.). Since it has been shown that Ti has positive effects on the phase boundaries, the equilibrium phases in the zirconia-titania-magnesia system are investigated (Saenko et al.). Furthermore, a new process for the production of (ultra)high-strength steels of the 3rd generation, quenching-deformation-partitioning, is discussed (Wendler et al.). For steels produced over a similar route (quenching and partitioning) the cyclic properties and fatigue life are presented (Droste et al.). Further work shows the behaviour of austenitic stainless steels under axial-torsional loading (Krause et al.) and crack growth under biaxial-planar fatigue loading (Wolf et al.). Finally, the electrochemical corrosion behaviour is studied using electrochemical noise and acoustic emission analysis (Kietov et al.). In order to enable future processing of the new composite materials, joining using electron beam technologies (Halbauer et al.) and simulation of the joining process are considered (Borrmann et al.). These articles present aspects of the current research work. Of course it is not possible to give a complete overview. Therefore, the readers are referred to the further literature. Finally, we would like to thank the German Research Foundation for the financial support of the work within SFB 799. Horst Biermann
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May 19, 2020
M.A Charpagne + 6
Open Access