HIGH-TEMPERATURE PERFORMANCE EVALUATION OF A DIRECTIONALLY SOLIDIFIEDNICKEL-BASE SUPERALLOY

The application of a new approach, design for performance, for high-te mperature alloy development, design analysis, and remaining life asses sment, based on short-time high-precision testing, is described in thi s paper. The material tested was a directionally solidified nickel-bas e alloy, GTD111. It was found that the creep strength at 850 degrees C was indeed superior to that of a competitive alloy, IN738, but was no t necessarily enhanced by the preferred alignment of grain boundaries and crystal orientation. In contrast, the fracture resistance at 800 d egrees C was improved in the longitudinal direction compared with tran sverse and diagonal orientations in terms of susceptibility to gas pha se embrittlement (GPE) by oxygen. Specimens cut transversely and diago nally to the growth direction were more sensitive to GPE than specimen s taken from conventionally cast IN738. The new conceptual framework a llows account to be taken of GPE and other embrittling phenomena, whic h may develop in service, leading to rational life management decision s for gas turbine users. Additionally, straightforward design analysis procedures can be developed from the test data, which for the first t ime allow separate measurements of creep strength and fracture resista nce to be used for performance evaluation.