Comparison of Single Crystal Superalloys for Turbine Blades Through TMF Tests

Abstract

The greatest advance in metal temperature and stress capability for turbine blades in the last thirty years has been the result of the development of directionnally solidified single crystal superalloys. Two groups of alloys, called first and second generation, have been developed. The second generation alloys were essentially developed to improve the creep resistance and the long time phase stability in order to allow increased operating temperatures. Creep resistance is not the only property to be considered for life prediction. In complex shaped highly cooled turbine blades, stresses of thermomechanical origin may become at least as important as the centrifugal stress causing the creep of the material during the stabilized regime of the engine cycle. Those thermomechanical stresses are generated in particular during aircraft take off and landing operations. A limited amount of work has been done to compare the performance of the two generations of single crystal alloys regarding thermomechanical fatigue resistance.