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Evaluation and Improvement of Coatings for Columbium Alloy Gas Turbine Engine Components. Part 2


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Data generated using laboratory tests such as oxidation-erosion, thermal fatigue ballistic impact, and wear-galling to simulate turbine engine environments are reported for 14 coated columbium alloy composites, 12 in preliminary screening evaluations, 3 of which were pursued through advanced evaluation, and 2 others involved only in the advanced evaluation. Applications considered were turbine vane and turbine blade airfoils operating in the 1800 - 2500 deg F temperature range and turbine blade roots at 1300-1600 deg F. Oxidation-erosion, thermal fatigue, and ballistic impact test results for five vane and blade airfoil coating-substrate systems are reported and reviewed through preliminary screening and, where applicable, coating improvement phases. The Sylvania SiCrTi slurry/B-66 alloy and Solar MoTi-Si(TNV-12SE4)/Cb-132M alloy systems demonstrated the best overall performance of the five systems evaluated. As a result of the advanced evaluation program, it was recommended that the Sylvania SiCrTi slurry coating be engine tested on columbium alloy turbine vanes in the final phase of the contract program. Both the TRW TiCr-Si/Cb-132M and the Sylvania SiCrTi/XB-88 systems demonstrated potential for turbine blade application based on adequate oxidation-erosion, thermal fatigue, and 2200 deg F mechanical fatigue, creep, and stress-rupture performance in advanced evaluation. However, low ductility was observed in tensile tests at intermediate temperatures (1300 - 1800 deg F). Since this characteristic would cause a high risk of premature failure during thermal cycling of a turbine blade, it was recommended that testing of coated columbium alloy turbine blades not be conducted under this contract. Of eight candidate turbine blade root systems evaluated, the Sylvania SiCrFe slurry coated alloy composites proved superior in 1300-1600 deg F oxidation, wear-galling resistance, and fatigue performance.



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