MEASUREMENT OF THE LATTICE MISFIT IN THE SINGLE-CRYSTAL NICKEL-BASED SUPERALLOYS CMSX-4, SRR99 AND SC16 BY CONVERGENT-BEAM ELECTRON-DIFFRACTION

Misfit measurements in the nickel based superalloys CMSX-4, SRR99 and SC16 have been per formed applying the CBED method. Due to the high la teral resolution of the method, lattice parameters of matrix and gamma ' phase could be measured directly. Use of an incident beam direction (1 1 19) ensured that even in thin matrix channels the electron beam d id not cross the interface and that dynamic effects were minimized. Th e results showed great differences of misfit values between the dendri tic and interdendritic region of the alloys, especially in CMSX-4. At -170 degrees C, CMSX-4 and SRR99 have negative misfit values while the value is positive in SC16. Stress relaxation, respectively, strain re laxation in the thin specimens could be compensated with the help of f inite element calculations. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.