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I am a PhD Researcher that focuses on characterising the microstructural behaviour of superalloys.

PINBOARD SUMMARY

Discover the impact that thermal barrier coatings have had on today’s turbine engines

In 10 seconds? In today’s aerospace industry the main drive for development is gas turbine efficiency. The way to achieve a greater efficiency is by operating at higher temperatures. Therefore, we need thermal barrier coatings to prevent the metallic components from degrading!

Don’t believe it? There has been an abundance of research carried out focusing on turbine engine efficiency….from increasing operating temperature range to finding novel techniques to enhance the properties of the TBC’s for longer lifetime - Just look at the articles.

What’s a thermal barrier coating? A thermal barrier coating (TBC) is a class of protective coatings, which act as an insulator to protect the base material from extreme temperatures, which could cause adverse effects to the alloys mechanical properties. The most commonly used TBC is YSZ – this is because zirconia stays stable at exceedingly high temperatures preventing phase transformation. However, the YSZ is only one layer of the coating there are in fact four layers in total!

So, what are the four layers?

Thermal barrier coatings consist of four layers; base metal, bond coat, thermally grown oxide and the top coat.

  • Base Metal – This is simply the metal of the part that you want to be protected from the heat i.e. a fan blade.
  • Bond Coat - The bond coat is required to cope with the residual stresses within the coating that can be caused by different co-efficient of thermal expansions between the metallic substrate and the ceramic top coat. Additionally, this layer has added functionality because it also protects the substrate from corrosion and oxidation.
  • Thermally Grown Oxide Layer – This layer grows at the interface between the bond coat and the topcoat, and in many instances is the cause for many TBC failures due to the thermally grown oxide layer cracking.
  • Topcoat – This layer acts as the insulator and is commonly YSZ due to phase stability, low heat conductivity (which is critical) and finally it’s co-efficient of thermal expansion.
8 ITEMS PINNED

Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray

Abstract: Abstract 7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.Abstract7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.

Pub.: 01 Jan '17, Pinned: 10 Apr '17