EXTRAPOLATION METHODS FOR PREDICTING THERMAL FATIGUE LIFE OF SINGLE CRYSTAL SUPERALLOYS

An extrapolation method for predicting thermal fatigue durability of single-crystal superalloys at temperatures lower than experimental ones is proposed based on the four-term deformation criterion of thermal fatigue failure. Verification of the proposed approach by results of separate tests of ZHS32, ZHS36 and VZHM4 alloys is carried out on plane corset specimens of different crystallographic orientations. It is shown that the error in determining the number of cycles for macrocrack initiation does not exceed one order of magnitude, while calculation by Manson’s formula of universal slopes that is widely used in practice can yield errors over two or three orders of magnitude.