Thermisch gespritzte Schichten im System Al₂O₃-Cr₂O₃-TiO₂- ein Update

Abstract

Die Einzeloxide im System Al2O3–Cr2O3–TiO2 und Zusammensetzungen der binären Teilsysteme sind neben dem Zirkonoxid die wichtigsten oxidkeramischen Werkstoffe für thermisch gespritzte Schichten. In diesem Beitrag werden wichtige Ergebnisse eigener Entwicklungsarbeiten der letzten Jahre zusammengefasst. Diese betreffen den Vergleich der Mikrostrukturen, Phasenzusammensetzungen und Eigenschaften von Schichten, die durch atmosphärisches Plasmaspritzen (APS) und Hochgeschwindigkeitsflammspritzen (HVOF) hergestellt wurden, aber auch vor allem die Möglichkeiten, die sich durch die Verwendung von Suspensionen als Spritzzusatz eröffnen. Besondere Aufmerksamkeit finden die Vorteile, die sich durch die Nutzung der binären Zusammensetzungen im System ergeben. Die tribologischen, elektrischen und Korrosionseigenschaften der Schichten werden diskutiert.

Microstructure and Sliding Wear Resistance of Plasma Sprayed Al2O3-Cr2O3-TiO2 Ternary Coatings from Blends of Single Oxides

“…Coatings sprayed from the single oxides and some commercially available binary compositions of the Al 2 O 3 -Cr 2 O 3 -TiO 2 system have multi-functional properties and are widely used as wear and as (sealed) corrosion resistant coatings. Depending on the composition, they are electrically insulating or conductive [1,2].…”

“…Each of the single oxides shows a specific material behavior during spraying, which is detrimental to the processing and/or coating properties [1,2].…”

“…An increase of the α-Al 2 O 3 content in the coatings is described as an important measure to improve the coating properties, such as wear, electrical, and corrosion resistance. Except the addition of other oxides (e.g., Cr 2 O 3 [8][9][10]), there are several technological measures for this, as the selection of special spray process conditions [11], use of suspensions [1,5] or heat post-treatments [12] as well as plasma-electrolytic oxidation of arc-sprayed and flame-sprayed aluminum coatings [13]. However, each of these technological measures has certain limitations and the stabilization of the α-Al 2 O 3 by a tailored powder would be favored.…”

“…However, each of these technological measures has certain limitations and the stabilization of the α-Al 2 O 3 by a tailored powder would be favored. Chromia has a low deposition efficiency due to oxidation from Cr 2 O 3 to volatile CrO 3 , which immediately reconverts to Cr 2 O 3 when cooling down [1,2,14]. Formation of Cr(VI)-oxyhydrates in wet atmospheres is another detrimental reaction [14,15].…”

“…Although the appearance of hexavalent chromium is below the maximum allowable concentrations under normal process conditions, increased safety regulations are permanently under discussion. By adding Al 2 O 3 [16] or TiO 2 [1,2] to Cr 2 O 3 and forming respective solid solutions, both the formation of hexavalent chromium is suppressed and the deposition efficiency is increased.…”