Coatings for High-Temperature Structural Materials Trends and Opportunities (1996) / Chapter Skim
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SUMMARY
SUMMARY
Pages 1-7
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have sufficient inherent resistance to the degradation mechanisms to prevent catastrophic reduction in service lifetime in the event of coating failure. Since the materials considered for future substrates may possess less inherent environmental resistance at higher temperatures, the importance of coatings in achieving performance will continue to grow.
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The main difficulty with TBCs is that the abrupt change in composition and properties at the interface tends to promote ceramic layer spallation. Electron-beam physical vapor deposition is often favored over plasma deposition for TBCs on turbine airfoils since it applies a smooth surface of better aerodynamic quality with less interference to cooling holes.
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The future trends for aircraft engine repairs will tend to parallel those of the industrial turbines with the further complication of thinner walls and more sophisticated cooling passages. Thinner walls in advanced components may preclude any shipping of the prior coating, potentially leading to a nonrepairable part, as is the case with many of the current turboprop and turboshaft high-pressure turbine blades.
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Thermal Barrier Coating Development TBCs reduce the severity of thermal transients and lower the substrate temperature, enhancing the thermal fatigue and creep capabilities of coated components. In addition, although TBCs do not provide significant reduction in oxygen transport to the substrate, the lower component temperature can lead to a reduction in oxidation and hot corrosion.
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methods can aid significantly in developing and qualifying coating systems, improving process control during coating operations, and characterizing the integrity of coated structure during turbine engine manufacture, in-service condition monitoring, and repair and overhaul operations. Since each of these applications has specialized requirements, no single NDE method will likely serve all purposes.
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Most advanced materials and design modifications will result in component structures with inherently less resistance to aggress~ve environmental attack than current superalloys, pushing the need for parallel development of improved coatings systems. Incremental improvements to current coating technologies are unlikely to meet the goals offuture-generation, higher-performance turbine engines.
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to achieve nanoscale structural control and characterization. Such techniques might be adapted for turbine coatings in order to improve coating quality and increase the cost effectiveness of coating processes for the manufacture of functionally graded coatings.
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