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Thermal Spray Conference - New Developments in Thermal Spray Coatings, Processes and Applications
Home > Educational Programs > Thermal Spray Session 4
Monday, November 16, 2009 • 9:00 AM – 4:30 PM
Chairs: Dan Hayden, Hayden Corporation; Bob Unger, Polymet Corporation
Member of AWS, FMA, SME, NAM, or PMA: $345
Nonmembers: $480 • Registration Code: W22
Room N230a
The American Welding Society and The International Thermal Spray Association are organizing the first Thermal Spray and Coatings Conference, to be held in conjunction with the 2009 FABTECH INTERNATIONAL & AWS WELDING SHOW Including METALFORM. The program is intended to introduce the process and its uses to new potential users with morning and afternoon sessions focusing on actual applications and new developments in thermal spray technology.
Session 4: New Developments in Thermal Spray Coatings and Equipment
Dense Ceramic Coatings Produced by Slurry Axial Plasma Spraying
2:35 PM – 2:55 PM
Michael Molnar, Mettech
Dense ceramic coatings are required for emerging applications such as solid oxide fuel cells (SOFCs), plasma erosion resistant coatings, and new thermal barrier coatings (TBCs), among others. These applications present significant challenges for traditional plasma spraying. Currently, plasma spraying uses powders in the range of 10-150 µm, and the coatings for common applications such as TBCs typically exhibit porosities in the range of 5-15%. Finer powders yield denser coatings with thinner lamellae splats when compared to traditionally sized thermal spray powders. However, feeding issues have prevented standard techniques from producing coatings using powders finer than 10 µm. By suspending these fine powders in liquid and injecting the solid/liquid slurry into the plasma plume, a reliable fine particle spray delivery mechanism that produces highly dense coating structures can be obtained. This paper presents the approach of Mettech to enable dense coatings by using axial feed and a new liquid feed system. A robust slurry coating process was demonstrated by the production of dense coatings primarily for SOFC and plasma erosion resistance applications.
Cermet and Ceramic Coatings with Novel Thermal Spraying Methods
2:55 PM – 3:15 PM
Junya Kitamura, Kazuto Sato, Nobuaki Kato and Hiroaki Mizuno, Fujimi Incorporated
Thick coatings of WC cermet materials are widely applied by high velocity oxygen fuel spraying (HVOF) due to their excellent mechanical properties. However, the coatings are still inferior to the sintered bulk WC for toughness due to degradation of the feedstock powders, such as decarburization of WC, oxidation and formation of a brittle metal binder by mixing of WC and Co. Novel spraying methods with lower flame temperature, such as cold spraying and warm spraying, are one of the candidates to overcome the problem. Recent studies on cold spraying and warm spraying (modified HVOF) are introduced for the WC-Co coatings in this presentation. Plasma spraying producing high temperature flame jet has been used for ceramic materials. Plasma sprayed ceramic coatings have problems mainly due to their low density (high porosity) that causes lower mechanical properties in general. Suspension plasma spraying (SPS), developed recently, is one of the techniques to attain dense coatings where a suspension with fine ceramic powders of less than 10 micron is fed into the plasma plume. Mechanical and functional properties of yttrium oxide coatings by the SPS are also introduced in this presentation.
Advanced Vacuum Plasma Spray (VPS) for Rapid and Safe Closeout of Cooling Channels for Liquid Rocket Engine Combustion Chambers
3:15 PM – 3:35 PM
Chris Power, Genie Products
Taking advantage of vacuum plasma spray (VPS) technology for building safe and durable cartridges for high temperature experiments in space furnaces, NASA's Marshall Space Flight Center (MSFC) and Genie Products, Inc. have been translating this VPS technology to building robust, long life liquid rocket engines. A subscale 5K (5,000 lb thrust) VPS formed chamber with a functional gradient material (FGM) hot wall, has now experienced 220 hot firing tests in pristine condition with no blanching (surface pulverization) or cooling channel cracks experienced in standard liquid rocket engines in less than 30 of the same hot firing tests. Normally, the 5K thruster combustion chamber is first VPS formed with a functional gradient material (FGM) hot wall in one continuous VPS operation. Cooling channels, then cut on the outside of the combustion chamber, are filled with a ceramic filler, VPS over-sprayed as a closeout, and the filler material removed by etching with a dilute acid. In building and testing larger engines, required by NASA for consideration in the space program, the next step chosen was a 40K (40,000 lb thrust) engine. A 40K thruster designed as a calorimeter was chosen because it could be used for measuring temperatures simultaneously with other NASA propulsion testing. Cooling channels in normal combustion chambers run parallel to the combustion flow. However, cooling channels in calorimeters run circumferentially and must be closed out by first filling the channels with wax and electrodepositing the closeout material around the outside surface. The electrode position process can take up to 12 months to close out the cooling channels on the Space Shuttle main engine. Taking advantage of the VPS process, the cooling channels on the 40K chamber were filled with wax and electrodeposited for five days. The calorimeter combustion chamber was then heated to remove the wax, VPS coated for several hours, and subsequently machined, ready for placing in a support jacket and hot fire testing.
Methods and Effects of Cooling Work Parts During WC-CoCr HVOF Coating
3:35 PM – 3:55 PM
Lisa A. Mercando and Zbig Zurecki, Air Products & Chemicals, Inc.
High-velocity oxygen fuel (HVOF) hardfacing of metallic work parts with WC-Co-type coating offers a performance and cost alternative to toxic chromium (Cr6+) plating. The cost competitiveness of HVOF hardfacing is, nevertheless, a strong function of production rate and deposition efficiency (DE) of feed powder. These are limited by significant heat input into substrate parts taking place during continuous HVOF coating which necessitates the use of forced air or gas cooling, frequently combined with additional cooling breaks in spraying. Thus, determination of the effect of cooling method on production rate and DE is industrially critical. Prior experiments with nitrogen cryo-aerosol cooling of landing gear during HVOF hardfacing using DJ2600 gun and SM5847 powder have demonstrated doubling of production rates and halving of powder consumption, as compared to those of the conventional air cooling, while depositing improved, less residually-stressed WC-10Co-4Cr coatings at increased DE. Present work compares effects of three different cooling methods on DE and substrate temperature during nonstop HVOF coating using JetKote-II Nova gun and JK120H powder: (1) forced air, (2) liquid CO2, and (3) N2 cryo-aerosol. It is found that the air cooling DE of 45%, measured per ISO 17836/2004, is increased to 48% with liquid CO2 and to 54% with N2 cryo-aerosol. Experimental results will be detailed and explained by the combination of oxidizing potential of cooling gases used and the average substrate temperature during coating.
Gun Mounts for the Articulated Robot; Fibonacci Comes Through Again
3:55 PM – 4:15 PM
Dale Moody, Plasma Powders and Systems
Many articulated robot gun mounts in use today were originally designed for gantry or X-Y traversing manipulators. The use of these basic mounts results in a constrained operating window for robot motion during thermal spray operations. In addition, articulated robots are often positioned in the thermal spray cell before the gun mount configuration is established. This can also result is a less-than-ideal thermal spray arrangement.
The paper discusses the disadvantage of using “Angle Iron” gun mounts and discusses optimum designs. Interestingly enough, the near optimum design is based on the “Golden Triangle”, a derivative of the Fibonacci Numbers series.
The importance of establishing the gun mount before determining the positioning of the robot in the work area will also be discussed.
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