Effect of Cyclic Strain/Temperature Exposure on Fatigue Life of Coated Turbine Alloys
Final rept. Aug 1983-Mar 1987
PRATT AND WHITNEY WEST PALM BEACH FL MATERIALS ENGINEERING LAB
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This program sought basic information about the behavior of coated superalloys versus strain-temperature history in high-temperature, thermal- mechanical exposure. The test plan was based on the observation that test cycle shape strongly impacts the thermal-mechanical-fatigue TMF behavior. We found that increasing T sub max. of the Type 1 cycle from 1900 to 2100 deg F shortened the initiation period for TMF cracking and reduced cycles to specimen failure by about 30 to 50 percent. A more radical change in cycle shape, namely a four- sided shaped cycle, was less mechanically damaging a factor of two but more severely oxidizing than Type 1 cycles between the same temperature and strain limits. Cyclic speed experiments showed that crack initiation and cycles-to- failure data were not strongly sensitive to testing speed in the range of 1 to 4 cycles per minute. Lower N sub f values for slow speed tests are believed to reflect crack growth in the substrate rather than coating effects. Shut-down steps and hold times at T sub max. and during cooldown from T sub max. generally decreased N sub f values. Coatings Coated Turbine Alloys Coated Superalloys Fatigue Life Cyclic Strain Temperature Exposure.
- Coatings, Colorants and Finishes
- Properties of Metals and Alloys