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| SPS™ Thermal Barrier NanoCoatings: what they do and how they do it |
Inframat's
porous ceramic thermal barrier coating (“TBC”),
is a nanocoating which exhibits a quantum leap in performance
in comparison to conventional TBCs. Its principal application
is for industrial and aircraft turbine engines where affordability
is paramount. TBCs essentially act as “blankets.”
These porous coatings are used to insulate hot section metallic
components (turbine blades, turbine vanes, combustors) from
the hot gas stream in all modern aircraft gas turbine engines
and in industrial gas turbine engines used for power generation.
TBCs enable a temperature reduction of as much as 160 °C
at the metal surface, thereby improving the durability of the
metal component and reducing engine fuel consumption. Current
TBCs, predominantly made from yttria-stabilized zirconia (“YSZ”),
are made by one of two processes: air plasma spray (APS) (see
Fig. 1) or electron beam physical vapor deposition (“EB-PVD”).
Historically,
APS TBCs have shown desirable low thermal conductivity, relatively
low cost and adequate durability but only for less demanding
applications. In contrast, EB-PVD TBCs have undesirable higher
thermal conductivity, considerably higher cost, but sufficiently
higher durability that they can be used to provide thermal protection
for the most demanding rotating turbine blade applications.
However, installation (capitalization) costs for an EB-PVD facility
are upwards of $20 MM, forcing market applications to be limited
to high margin products. The APS and EB-PVD processes have been
in use and under continuous development for several decades.
But, each approach is less than optimal.
Despite extensive development efforts over many years, no superior
processes for applying TBCs have been identified, until our
new product - the Solution Plasma Spray (“SPS”)
Coating. The SPS Coating (Fig 2 inner dimension) combines the
low thermal conductivity and low cost of APS TBCs with the high
durability of EB-PVD TBCs. In addition to servicing traditional
high end engine products, this unique combination of high performance
and low cost is expected to enable the manufacture of high performance
TBCs for low margin applications that were, until now, not economically
viable, e.g., small engines.
Traditional
Plasma Spray is based upon the use of powder feedstocks. In
distinction, the SPS Process, a precursor solution, containing
zirconium and yttrium in the right proportion, is atomized to
form liquid droplets and injected in the hot plasma flame (see
Fig. 3).
The droplets undergo
a series of physical and chemical reactions and are deposited
on a metallic substrate at high velocity to form a TBC. Our
solution feedstock delivery system has been retrofitted for
existing commercial plasma spray guns at a very modest cost
(a few thousand dollars). Our technology has been developed
so that the hardware is fully integrable with existing commercial
plasma spray equipment.
SPS coatings
show superior thermal cycling durability compared to all commercial
TBCs (see Fig. 4). A thermal cycle life of approx. 1,000 cycles
is shown for SPS in comparison to 400 for APS and 650 cycles
for EB-PVD. The SPS TBC has a unique microstructure (Fig. 5
triptych) consisting of nanometer- and micron-size pores, through-thickness
cracks, and the absence of coarse, brittle “splat”
boundaries found in commercial APS TBCs. Only the SPS TBC is
comprised of equiaxial nanograins (observable in TEM), which
are approximately 20 – 50 nm in dimension. This unique
microstructure provides superior toughness and strain tolerance
to withstand the high thermal strains in gas turbine engines.
Not just an incremental improvement, this product truly delivers
on the much-publicized promise of nanotechnology.
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First reduced
to practice at Inframat’s Thermal Spray Lab in 1998, Inframat
and the U.S. Navy jointly filed a U.S. Patent for a Solution
Plasma Spray process to radically alter traditional thermal
spray coating technology by abandoning conventional powder feedstocks
and exploring direct injection of solution feedstocks into the
plasma gun. This concept has been under development in collaboration
with the University of Connecticut through funding originating
from both the DOE and the U.S. Navy since November, 2001. This
technology falls under a world wide exclusive license granted
from UConn to Inframat effective June, 1997.
To
view a video demo on our SPSTM coating, click below:
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