Microstructure, Processing, Performance Relationships for High Temperature Coatings

Conference · Fri May 01 04:00:00 EDT 2009

OSTI ID:961926

Lillo, Thomas; Wright, Richard

HVOF coatings have shown high resistance to corrosion in fossil energy applications and it is generally accepted that mechanical failure, e.g. cracking or spalling, ultimately will determine coating lifetime. The high velocity oxygen-fuel method (HVOF) for applying coatings is one of the most commercially viable and allows the control of various parameters including powder particle velocity and temperature which influence coating properties, such as residual stress, bond coat strength and microstructure. The mechanical durability of coatings is being assessed using a dual eddy current coil method to monitor crack formation in real time during thermal cycling. Absolute impedence signals from two coils, which interrogate two different areas on the sample, are collected. Crack detection can be determined from the differential signal generated from these absolute signals. The coils are operated at two different frequencies, resulting in two differential signals used for crack detection. Currently this crack detection method is being used to elucidate the influence of thermal cycling temperature and coating thickness on cracking. Recent results (cycles to failure) will be presented for FeAl coatings thermally sprayed (HVOF) onto carbon steel to two coating thicknesses (160 microns and 250 microns thick) and subsequently cycled at temperatures up to 700oC. Thinner coatings exhibit greater resistance to cracking. Ultimately the resistance to cracking will be used to explore the relationship between HVOF spraying parameters, the mechanical properties of the coating and coating bond strength to develop optimized thermal spray parameters. To this end thermal spray coatings (FeAl and Fe3Al) have been applied to additional alloy substrates (Grade 91 steel, 316 SS, etc.) relevant to the fossil industry. Future plans also include a direct comparison to conventional weld overlay coatings currently used in the industry as well as exploration of new coatings. The room temperature mechanical strength and coating adhesion to the substrate is also of considerable importance. Eddy current methods are being developed to detect coating failure during room temperature tensile tests to optimize surface preparation as well as aid in the optimization of the HVOF thermal spray parameters.

• Research Organization: Idaho National Laboratory (INL)
• Sponsoring Organization: DOE - FE
• DOE Contract Number: AC07-99ID13727
• OSTI ID: 961926
• Report Number(s): INL/CON-09-15875
• Country of Publication: United States
• Language: English

Related Subjects

20 FOSSIL-FUELED POWER PLANTS
36 MATERIALS SCIENCE
ADHESION
ALLOYS
CARBON STEELS
COATINGS
CORROSION
DETECTION
EDDY CURRENTS
EXPLORATION
Iron Aluminides
LIFETIME
MECHANICAL PROPERTIES
MICROSTRUCTURE
MONITORS
Metallic Coatings
OPTIMIZATION
SPRAY COATING
SUBSTRATES
THERMAL CYCLING
THICKNESS
Thermal Spray coatings
VELOCITY