In-situ synthesis of Y 2 W 3 O 12 within a Co-based superalloy powder mixture In this work, the synthesis of the negative thermal expansion ceramic Y 2 W 3 O 12 within a Co-based superalloy was analyzed in detail. On the basis of thermal analysis of the synthesis from the feedstock powders Y 2 O 3 and WO 3 further experiments were conducted. Thermal behavior and stability of different mixtures of the powders Y 2 O 3 , WO 3 and the Co-based superalloy were investigated. The qualitative and quantitative results of the synthesis separately and within the superalloy are presented as achieved by energy dispersive X-ray analysis, X-ray powder diffraction, differential thermal analysis and thermal gravimetric analysis. It was found that the synthesis of yttrium tungstate inside the Co-based superalloy is possible with a defined temperature program and a simple basic production process of powder mixtures.

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Although well known, corrosion processes are still a problem for technical constructions. Although different coating technologies and materials have been developed and approved to prevent base metals from being destroyed, industrial applications dealing with aggressive atmospheres, require new material concepts to protect them. Using the example of two different applications, on the one hand heat exchangers in waste incineration plants and on the other hand permanent-molds used for casting non-ferrous metals, innovative material concepts for corrosion protection are given. Heat exchangers in waste incineration plants are exposed to highly corrosive atmospheres especially due to high temperatures in combination with chlorine containing atmospheres. Wire arc sprayed coatings made of iron-based alloys containing chromium, silicon and boron provide a new approach for these applications and, compared to standard nickel-based alloys, they are cheaper and potentially more resistant coatings. In the case of permanent-molds corrosion, mainly occurs due to direct dissolution of the base material by the liquid metal. Tungsten-based pseudoalloys are known to be extremely resistant against liquid metals and therefore sintered inlays of these materials are sometimes used in extremely stressed regions. These materials have not previously been applied as a coating. Therefore different coating technologies have to be considered and the metallurgical behaviour of the material due to the associated higher cooling rates must be investigated.

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This work investigates some of the unique properties that can be achieved by combining materials with positive and negative thermal expansion coefficients. In the experiments, different mixtures of MCrAlY, WO3, and Y2O3 powders are deposited on stainless steel substrates by laser cladding and HVOF spraying. To facilitate the formation of negative expansion coefficient particles in a positive expansion coefficient matrix, nucleation centers are created by ion implantation followed by heat treating. SEM examination and XRD analysis of the coatings obtained confirm the viability of the processing approach.