Abradable seals have been used in jet engines since the late 1960's. Today abradable seals are seeing applications not only in low pressure and high pressure sections of the compressor but also in the high pressure turbine module of jet engines and are gaining ever more attention in industrial gas turbines. Thermal spraying is a relative simple and cost effective means to apply abradable seals. These work by minimizing gaps between rotating and stationary components by allowing the rotating parts to cut into the stationary ones. The types of coatings employed are zirconia based abradable material systems with polymer and, in some cases, hexagonal boron nitride additions. The coatings are designed to work at service temperatures of up to 1200 °C. The objective of this paper is to review various types of commercial and experimental ceramic abradable systems and to assess their performance profiles. The paper will review yttria stabilized zirconia based systems with modified polymer additions and with variable particle sizes of the ceramic phase. Alternative stabilizers and their influence on key coating properties such as thermal shock resistance and abradability will be studied. The paper will also review the influence of plasma spray parameters on coating properties and study the general influence of coating porosity on coating erosion properties and abradability.

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