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:\[\begin{array}{l}{{\rm{[011]}}_{{\rm{vc}}}}{\rm{||[011}}{{\rm{]}}_{\rm{M}}}{\rm{||[011}}{{\rm{]}}_{{{\rm{M}}_{{\rm{23}}}}{{\rm{C}}_{\rm{6}}}}}\\{{\rm{[111]}}_{{\rm{vc}}}}{\rm{||[111}}{{\rm{]}}_{\rm{M}}}{\rm{||[111}}{{\rm{]}}_{{{\rm{M}}_{{\rm{23}}}}{{\rm{C}}_{\rm{6}}}}}\\{{\rm{[200]}}_{{\rm{vc}}}}{\rm{||[200}}{{\rm{]}}_{\rm{M}}}{\rm{||[200}}{{\rm{]}}_{{{\rm{M}}_{{\rm{23}}}}{{\rm{C}}_{\rm{6}}}}}\end{array}\]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.