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Life Prediction of Turbine Blade Nickel Base Superalloy Single Crystals.
Final rept. 1 Oct 83-31 Mar 84,
UNIVERSAL ENERGY SYSTEMS INC DAYTON OH
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The result of Phase I research is reported along with a brief discussion on the technical feasibility of the approach. The objective of this research is to develop life prediction method for single crystal Rene N4 through mechanistic and microstructural approaches. LCF tests were performed at 1093C. The effect of three strain ranges, hold-time and coating were considered. Surface replicas were taken in the early part of the tests. Fracture surfaces, longitudinal sections and thin foils were examined using SEM, TEM, and EDAX techniques. The precipitates gamma coarsened during the test. There was an increase in the tensile mean stress. In all specimens almost cracks were surface-nucleated. While the micropores appear to be the nucleation sites in the uncoated sample, the nature of nucleation sites on the coating surfaces is not clear. Transverse cracks along the gage, and several secondary cracks below the fracture surfaces were observed. Oxides covered the fracture surfaces. Coatings did not affect the LCF lives. The LCF lives followed a linear relation between strain range and cycles to failure. The Phase I results and the results of Phase II if funded will have immediate application in the component retirement programs of the U.S. Air Force and Navair, and in the alloy development programs of General Electric Co., Cincinnati, OH.
APPROVED FOR PUBLIC RELEASE