Recent developments in the designing of deposition of thermal barrier coatings – A review

Abstract

The thermal barrier coatings (TBCs) provide insulation to the components of gas turbine by providing higher amount of thermal energy and also reduce the cooling requirement of the top ceramic surface. The top ceramic coat plays a significant role in surging the efficiency of the TBCs. The 8 wt% Yttria partially stabilized zirconia (YSZ) is the top coat material is widely used because of its ability to withstand aggressive conditions of high temperature and pressure. Air plasma Spraying (APS) technique frequently used in gas turbine industry to deposit 8 wt%YSZ TBCs. There are some important spray parameters which play very important role in the deposition of TBCs such as powder feed rate (g/min), current (A), voltage (V), Power (KW) and standoff/spray distance (mm), and these parameters help to regulate the phase composition, isothermal thermal stability, improved microstructure, corrosion resistance and mechanical properties like residual stresses and bonding strength. Recently new surface modification techniques have been developed such as plasma-enhanced chemical vapour deposition (PECVD), electrostatic spray assisted vapour deposition (ESAVD), and solution precursor plasma spray (SPPS), sol-gel and suspension plasma spraying (SPS). These processes enhance the features of developed coatings which include the formation of vertical cracks by utilizing segmentation process and so on. Furthermore, the effect of varying the deposition process parameters like substrate temperature low plasma gun speed, high passage thickness, contact area between splats have been discussed. This review gives a good understanding about the TBCs and inspires researchers to find new ideas for the improvement in this field.