NASA expresses interest in made in India tech for spacecrafts
A new thermal spray coating technology used for gas turbine engine in spacecrafts developed by a Rajasthan-based researcher has caught the attention of a NASA scientist.
Dr Tailor developed the controlled segmented Yttria Stabilised Zirconia (YSZ)-Plasma sprayed coating technology, which according to him could reduce the thermal spray coating cost by almost 50 per cent. “In simple language, vertical cracks (segmentation) in the coating are beneficial for gas turbine engine application used in spacecrafts.
Current method of developing cracks
Researchers are developing such cracks through very expensive processes (in several crore) and cracks are generated during the coating deposition process, and crack generation is not controllable .
Cracks can be classified into vertical and horizontal ones and they have opposite impact on the properties of TBCs. Vertical cracks reduce the residual stress in the top coat and provide strain tolerance. On the contrary, horizontal cracks trigger delamination of the top coat.
Thermal barrier coatings (TBCs)
These are one of the most widely applied coating systems to improve thermal, oxidation and corrosion resistances of metallic components which are used in the high temperature sections of industrial equipment such as gas turbines and aero-engines.
TBCs typically consists of three layers
yttria-stabilized zirconia (YSZ) top coat, MCrAlY (M is typically Ni, Co or their mixture) bond coat and Ni- or Co-based superalloy substrate.
There are two major deposition methods in industry for the top coating: atmospheric plasma spraying (APS) and electron-beam physical vapor deposition (EB-PVD).
APS provides advantages such as low cost, high deposition rate and applicability over large areas whereas EB-PVD is capable of producing columnar-structured coatings with high strain tolerance. The deposits fabricated by APS generally consist of a multitude of pancake-like lamellae called ‘splats’, formed by flattening and solidification of liquid droplets.
Dr Tailor is the deputy editor-in-chief of the Journal of Materials Science and Surface Engineering, and chief editor of the Journal of Thermal Spray and Engineering.