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The filtration of molten metal using ceramic foam filters (CFF) is a purification method often used by the aluminum industry to meet the increasing demands the melt quality. CFFs are in most cases produced by the replica method using polyurethane foam templates, which are coated with a ceramic slurry of targeted composition before being sintered into its final structure. Despite the key role of CFFs in view of metal cleanliness, there are only a few quality parameters for their evaluation. In the present study, an overview of the different material properties essential for CFFs, suitable measurement methods, and their limitations are presented. The focuses of this work are the different densities of ceramic foams and the thermal expansion coefficient measured by dilatometry, as well as the filter porosities and microstructure measured through mercury intrusion porosimetry and computer tomography, respectively. Moreover, elastic (Young’s Modulus) and mechanical properties (compressive strength) are discussed.

The present contribution focuses on the development of composite materials using innovative ceramic casting technologies. Within this work different processing routes, the relevance of their process parameters as well as the resulting mechanical and microstructural characteristics are discussed. The successfully developed TRIP-matrix foams as well as full beads reinforced with 5 and 10 vol.% zirconia achieve higher compressive strengths and energy absorption during deformation in comparison to the pure metal materials as references. The functionally graded beads allowed a compression of up to 20% with corresponding specific energy absorption of 10.7 kJ/kg. In a further approach, metal-matrix composites have been generated via paper-manufacturing technology. The partial replacement of cellulose fibers by commercially available zirconia fibers resulted in fiber reinforced TRIP-matrix composites with an increased tensile strength of approx. 33% as compared to the pure metal material as reference. Large-size ceramic matrix composites with high potential for applications requiring sufficient wear and thermal shock resistance have been successfully prepared via pressure slip casting. The last topic is concerned with the development of yttria-stabilized zirconia fibers with a tailored phase composition (monoclinic-tetragonal-cubic) via electrospinning.

The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method. The effect of the combination with focused ion beam sample preparation was determined in this work. In addition metal matrix compositemetal matrix composite honeycombs and foams as well as beads were investigated. The foams and honeycombs were composed of austenitic steel exhibiting TRansformation Induced Plasticity (TRIP) and magnesia partially stabilized zirconia. Both components exhibit martensitic phase transformation during deformation, thus generating the potential for improved mechanical properties such as strength, ductility, and energy absorption capability. The aim of these investigations was to show that stress-assisted phase transformations within the ceramic reinforcement correspond to strong local deformation, and to determine whether they can trigger martensitic phase transformations in the steel matrix. To this end, in situ interrupted compression experiments were performed in an X-ray Computed Tomography Device (XCT). By using a recently developed reconstruction algorithm, local deformation was calculated and regions of interest were defined. Corresponding cross sections were prepared and used to analyze the local phase composition by electron backscatter diffraction. The results show a strong correlation between local deformation and phase transformation.

Metal-Matrix-Composites (MMCs) based on steel with certain ceramic additions offer a wide range of applications in automotive, construction, and mechanical engineering. These MMCs combine the specific properties of steels such as their room temperature deformation behavior with the advantageous hard but brittle ceramic reinforcements which makes them favorable in crash-absorbing or strengthening components. However, common technologies such as casting or infiltration of ceramic preforms by metal melts suffer from the differences between metal and ceramic material characteristics involved during material processing and from geometrical restrictions. The adaption of the ceramics-derived extrusion technology at ambient temperature on materials established in the powder metallurgy (PM) enables an efficient manufacturing process of advanced fine-grained materials with particularly cellular (lightweight) structures as well as bulk specimens. Using powder raw materials enables a wide range of material combinations between TRIP/TWIP steels and various ceramic components considering the pronounced material characteristics of the composite. Knowing the influence of the raw materials, the processing parameters for shaping and the indispensable thermal processing transforming the formed powders into a solid material is crucial for proper manufacturing of MMCs with tailored characteristics. The joining process for these components extends the applicability of the investigated PM-MMCs.

Although it is undisputed that the filtration of aluminum melt inside ceramic foam filters is influenced by the wetting behavior between the liquid melt and the material of the filter coating, experimental proof is still pending. For the present study, the contact angle of an AlSi7Mg alloy on substrates made of Al2O3, MgAl2O4, 3Al2O3·2SiO2 and TiO2 was measured by the sessile drop method at 730 °C using non-contact heating and capillary purification technique. The contact angles were compared with filtration efficiencies of filters with identical coating composition measured during filtration trials performed at a pilot casting line. For inclusions smaller than 110 µm, a correlation between contact angle and filtration efficiency was observed. Furthermore, adhesion forces of alumina inclusions on the four coating materials were experimentally determined using atomic force microscopy in a water-based model system. For inclusions larger than 70 µm, the filtration efficiency correlates with the measured adhesion force.

Melt cleanliness is essential for high quality aluminum production. The main cleanliness criteria are the content of dissolved hydrogen as well as the content of non-metallic inclusions. The latter may impair the castability of the aluminum melt as well as the mechanical properties and the machinability of the aluminum castings. A simple and efficient way to remove non-metallic inclusions is the application of filters during the casting process. The influence of the filter roughness on the filtration is undisputed but experimental proof is still pending. Filters with three different levels of roughness were subjected in filtration trials in a filtration pilot setup at Hydro (Bonn, Germany) allowing determination of the inclusion removal efficiency by the application of two LiMCA devices. In addition to the LiMCA measurements, PoDFA, Alscan measurements and investigations of the casted aluminum were done.

The quality requirements of aluminium products are constantly increasing. It is critical that ingots and billets have the least amount of inclusions in the as-cast product. Filtration is therefore applied to all critical products, ceramic foam filtration (CFF) being the most frequently used technique. In an attempt to increase inclusion capture by CFF the influence of the filter surface chemistry on the filtration efficiency of aluminium alloys has been evaluated. Lab scale filters have been produced with coatings of different chemical composition. The filters have been characterized prior to usage and lab scale casts have been made on a pilot unit in conjunction with two LiMCA for inclusion removal efficiency determination. The paper will present the results from the characterization done and the observations will be discussed.

The effect of temperature and elemental concentrations of phosphorous, sulphur and titanium in high alloyed Cr-Mn-Ni TRIP/TWIP steels (16 %Cr, 7 %Mn, 6 % Ni) on the wettability of MgO partially stabilized zirconia (Mg-PSZ) substrates was studied. The investigation of the wetting behavior is of a major importance of the infiltration of steel into open foam ceramics and in interfacial contact of steel & ceramic powder in the spark plasma sintering. The interfacial reaction was characterized using X-ray and secondary neutral mass spectrometry analysis. The contact angle was investigated between 1500 ℃ and 1600 ℃ in argon (99.999 vol% Ar) atmosphere and was found to decrease with increasing temperature. At 1600 ℃ sulphur decreased the contact angle from 103 ° (100 ppm S) to 92 ° (1000 ppm S) in Fe-Cr-Mn-Ni. Increasing phosphorous content was found to increase the interfacial oxygen content in samples and the contact angle decreased to ca. 97 °. For titanium alloyed Cr-Mn-Ni sample, a TixOy interfacial layer was found after experiments and the contact angle was ca. 87 ° at maximum Ti content of 0.232 %.