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.

Yttria Partially Stabilized Zirconia (YPSZ) coatings are used as Thermal Barrier Coatings (TBCs) because of their capability to improve gas turbine performance by allowing higher turbine inlet temperature and reduced cooling air flow. Usually, YPSZ layers are applied by plasma spray on Ni-based superalloys pre-coated with a bond coat layer of MCrAlY, where M is Co, Ni, or both. In this work we used Raman spectroscopy to study the performance of TBCs during thermal cycling at two different temperature (1273K and 1373K). Raman scattering is capable of detecting monoclinic zirconia and to analyze residual stresses of the coatings with an higher sensitivity than traditional X-ray diffraction measurements. Raman spectra were analyzed by deconvolution methods in order to study the evolution of the relative intensities and position of different bands. We found that the position of the 635 cm-1 band shifts to higher values of wave number during thermal cycling and by comparing this data with those reported in literature, it is possible to retrieve the value of residual stresses in zirconia coating. We also observed a relation between the intensities of the bands at 602 cm-1 and 635 cm-1 band and the number of thermal cycles performed.