Dynamic, In Situ Generated Interfaces Between Carbon‐Bonded Alumina Filters and Steel During Spark Plasma Sintering/Field‐Assisted Sintering

Abstract

The aim of this study was to analyze possible reactions taking place during filtration of steel melts. The heterogeneous reactions and interface creation during short-time contact of liquid steel and newly developed carbon bonded alumina ceramic filter (Al 2 O 3 -C) were examined. The samples were produced using spark plasma sintering (SPS) to assure the absence of liquid convection. The production of the samples included very high heating rates of up to 1000 K min À1 , short holding times just above liquidus temperature and a rapid cooling. The focus of the research was put on the inorganic inclusions (endogenous as well as exogenous), agglomerates, and phase formation. Exogenous inclusions (Al 2 O 3 ) were added to the steel grade 42CrMo4 by a ball milling process. The results indicate the formation of MnS inclusions due to the high sulfur content in the used steel. The formation took place at the interfaces between steel and ceramic and at the grain boundaries within the steel. Penetration of the porous ceramic body by the steel was identified. Exogenous Al 2 O 3 inclusions were found to agglomerate, adhere at the steel/Al 2 O 3 -C interfaces and tended to float on top of the melt.

Functionalized Carbon‐Bonded Filters with an Open Porous Alumina Coating: Impact of Time on Interactions and Steel Cleanliness

“…Thus, some steel might have moved through the coating material and might have contributed to these microstructural changes. Similar observations have been reported by [18,19,24,25] on carbon-bonded alumina and also on coated Al 2 O 3 -C filters. [24] According to them, these changes emanated from decarburization that had been triggered by iron acting as catalyst.…”

“…Spark Plasma Sintering Trials Pieces of alumina coated filters and a 42CrMo4 steel powder (see Table 2) were heat-treated in an SPS unit HPD 25 (FCT Systeme GmbH, Germany). The setup was similar to the procedure described by Salomon et al [19] Also, hollow ceramic cylinders made of the Al 2 O 3 -C filter material served as sintering molds. They were filled with the steel powder and the filter sample.…”

“…[24] According to them, these changes emanated from decarburization that had been triggered by iron acting as catalyst. [13,18,19,24,25] Section 4 describes the decarburization in more details. Despite some cracks, which were probably caused by the strong thermo-shock, no distinct changes were observed at the coating/steel interface after 1 min testing time.…”

“…Consequently, chemical reactions at the interface can be examined as being almost unaffected by mechanical attack or interlocking of inclusions on the filter surface. [19] Second, immersion tests were carried out with immersion times ranging from 10 to 120 s using a steel casting simulator. Due to the inductive heating, a flow within the melt was created in such a way that the melt streamed on the rotating filter.…”

Comparison of Interfacial Reactions Between AlSi7Mg and Alumina Filter After Casting and Spark Plasma Sintering**

“…In another article that is featured in this special issue of Advanced Engineering Materials , the SPS setup used also for this study was described in detail. A hollow cylinder made of the alumina ceramic was filled with the powder of the aluminum alloy.…”