Thermal Barrier Coatings
(TBC) are thermally insulating coating systems protecting the
substrate from the hotter temperatures of the surrounding environment.
They are used in heavy diesel engines, some gasoline powered engines
and in both aero and stationary gas turbines. When properly applied
they can provide a 300°F (149°C) temperature difference
between their outer surface and their base metal interface.
TBC’s are complex coating systems consisting
of two (2) or more layers of sprayed material. The initial coating
deposited onto the substrate is generally an MCrAlY metallic alloy,
performing the function of a bond coat while also offering hot
corrosion and oxidation protection. Selection is based on how
its coefficient of thermal expansion matches that of the host
metal. Subsequent layers may be wholly refractory oxides or blends
of the MCrAlY with the ceramic component.
Typical bond coat materials for TBC’s
include:
· CoCrAlY
· CoNiCrAlY
· FeCrAlY
· NiCrAlY
· NiCoCralY
· MCrAlY modifications with silicon, platinum, yttrium,
tantalum
· Exothermic MCrAlY’s
· Nickel-chromium alloys
Metallic oxides used for the insulating layer
are:
· 22% magnesia stabilized zirconia
· 6% yttria stabilized zirconia
· 12% yttria stabilized zirconia
· 20% yttria stabilized zirconia
