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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.

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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