Influence of carbon content and coking temperature on the biaxial flexural strength of carbon-bonded alumina at elevated temperatures

Open cell ceramic foam filters are used for metal melt filtration to enhance the quality of cast products by reducing non-metallic inclusions and generating calm mold fill with less turbulences. A new generation of filters made of carbon-bonded alumina show an increased thermal shock resistance but a lower strength. The filters have to withstand high thermal and mechanical loads due to the filtration process, whereas a temperature dependent mechanical characterization of the bulk material is required. This contribution concentrates on the influence of carbon content and coking temperature, which are two important manufacturing process parameters. In the ball on three balls test miniaturized disk-shaped specimens are loaded with a spherical tipped punch at temperatures up to 1500 degrees C until failure occurs. The fracture stress is calculated and used to analyze the material strength by means of Weibull distribution. Two different mechanisms are identified, which change the micro-structure and therewith the strength of the material. Additionally, Raman spectroscopy supports the interpretation of the achieved results of the mechanically tested specimens. (C) 2020 Elsevier Ltd. All rights reserved.