Abstract: Regarding corrosion resistant crucibles and shell molds for titanium investment casting, recent research focused on suitable materials based on calcium zirconate (CaZrO3) as well as on novel technologies such as spray coating. Complex cast parts of Ti6Al4V without hard and brittle alpha-case layer were successfully produced. This overview also shows current trends, for example shell mold recycling and advanced technologies for microstructure functionalization such as flame spraying and electrospinning.

Abstract: Regarding corrosion-resistant crucibles and shell molds for titanium investment casting, recent research focused on suitable materials based on calcium zirconate (CaZrO3) and novel technologies, such as spray coating. Complex cast parts of Ti6Al4V without a hard and brittle alpha-case layer were successfully produced. This overview also shows current trends, for example shell mold recycling and advanced technologies for microstructure functionalization such as flame spraying and electrospinning.

Calcium zirconate refractories exhibit a promisingly high corrosion resistance in contact with titanium alloy melts. In the present article, we improved the thermomechanical properties of calcium zirconate based refractories by altering their microstructure and chemical composition. In a full factorial experimental design we investigated the effects of an insitu phase formation, of the addition of coarse grained MgO aggregates as well as the addition of SrCO3. Based on these factors, the chemical, physical, mechanical and thermomechanical properties as well as the resulting microstructure were thoroughly characterized. Strikingly, the addition of SrCO3 resulted in significantly improved mechanical properties before and after thermal shock. The improved thermal shock resistance can be attributed to a lower determined thermal expansion coefficient, a homogeneous pore size distribution with a reduced pore size and a better bonding between the matrix and the coarse grained aggregates.

Kohlenstoffgebundenes Aluminiumoxid ist ein wichtiges Feuerfestmaterial z.B. in der Stahlindustrie. Die Herstellung dieser Formwerkstoffe erfolgt derzeit im Pressverfahren. Der Druckschlickerguss könnte ein neuer Ansatz für die Herstellung solcher Produkte mit neuem Potenzial in der Chargenzusammensetzung sein. In dieser Studie konnten die ersten kohlenstoffhaltigen, grobkörnigen Aluminiumoxidplatten gegossen werden und sie zeigten vielversprechende thermomechanische Eigenschaften. Die Entwicklung vom Schlicker zur gegossenen Platte ist in dieser Arbeit dargestellt.

The present paper analysed the formation of calcium zirconate from zirconium dioxide and calcium hydroxide through solid state reaction. Different mole ratios and sintering temperatures are investigated. The sintering temperature was reduced to 1200 degrees C. Due to the decomposition process of the calcia source during firing the volume expansion in the sintered samples was remarkable. A good homogenisation of the raw mixture is necessary to obtain a complete reaction of the material. The microstructure of the calcium zirconate gained from calcium hydroxide and from calcium carbonate did not differ. Moreover, a difference in reactivity due to varying microstructure and temperature of decomposition between the different calcia sources could not be determined. Thus calcium carbonate is less hazardous and resulted in a higher yield of calcium zirconate compared to calcium hydroxide as calcia source.

Calcium zirconate (CaZrO3) is a promising refractory material to melt titanium alloys. Therefore the present study investigated refractory castables based on CaZrO3 to allow an upscaling to larger melting crucibles and refractory linings. The study first included the processing optimization of the refractory castable containing calcium aluminate cement using a full factorial experimental design. Then the physical, chemical, mechanical and thermomechanical properties that determine the practical application of the castable were analyzed. The properties were generally similar to the ones of uniaxially pressed refractories based on CaZrO3. Nevertheless, the matrix containing calcium aluminates caused a pronounced sintering shrinkage leading to a smaller apparent porosity and a lower refractoriness compared to uniaxially pressed refractories. Finally, melting crucibles with an inner volume of 900 ml were successfully manufactured. Thus, this study provides an effective framework for the further development of large CaZrO3 refractories. (C) 2018 Elsevier Ltd. All rights reserved.

Carbon bonded alumina is an important refractory material for example in the steel industry. The production of these shaped materials is currently press forming. Pressure slip casting could be a new approach for manufacturing such products with new potential in the batch composition. In this study the first carbon containing, coarse grained alumina tiles could be casted and showed promising thermomechanical properties. The development from the slurry to the casted plate is shown within this work.

This study investigates chemical, physical, mechanical, and thermomechanical properties of calcium zirconate (CaZrO3) refractories. The applied fused raw material contained some residual cubic zirconia, which impairs the corrosion resistance of CaZrO3 refractories. To adjust the stoichiometry, CaCO3 was added. Furthermore, stoichiometric amounts of CaCO3/monoclinic ZrO2 were added to promote an in situ pore formation without altering the phase composition. After firing cubic zirconia was only found in the coarse grained aggregates. CaCO3 additions increased the apparent porosity and reduced the thermal expansion coefficient due to the stoichiometric adjustment. Surprisingly, a higher porosity did not result in an improved thermal shock resistance, which can be attributed to a shift to larger pore sizes. This might cause a lower crack density, which is usually associated with a reduced thermal shock resistance. Future work will address the formation of smaller pores and the evaluation of the thermal shock resistance under practical conditions.