Precipitates of VC M₂₃C₆ and Stress Rupture Notch Sensitivity of Superalloy GH36

The structure analyses of two GH36 superalloy turbine disks with different heat treatments were conducted by thin foil TEM. The preci-tates in GH36 super alloy were identified as VG, M₂₃C₆ and NbC by SAD. Electron diffraction patterns show the orintation relationship between precipitates and matrix as following:\\beginarrayl\rm011_\rmvc\rm||011\rm_\rmM\rm||011\rm_\rmM_\rm23\rmC_\rm6\\\rm111_\rmvc\rm||111\rm_\rmM\rm||111\rm_\rmM_\rm23\rmC_\rm6\\\rm200_\rmvc\rm||200\rm_\rmM\rm||200\rm_\rmM_\rm23\rmC_\rm6\endarray\Moire patterns and dark field show that the size of VC precipitates after normal heat treatment varies from 3 to 12nm. The size of VC after superimposed higher temperature aging grows in a few nm larger and more M₂₃C₆ carbide precipitates in alloy than norma heat treatment. Thus, the yield stress and stress rupture strength decrease, but the stress rupture notch sensitivity has been improved.