MC Carbides in the Hf Containing Ni Based Superalloy MarM002

Abstract

Unexposed MarM002 alloy turbine blades and blades exposed at 700-1000oC for up to 250 days were studied by TEM, SEM, EDX and XRD. The shapes, distribution and compositions of the MC carbides do not vary significantly during exposure at 700 and 800oC. All MC carbides contain significant amounts of Hf, Ta, Ti and W, and they are present with a very broad range of compositions. The latter is caused by a miscibility gap in the MC carbide phase which causes the formation of MC carbides to shift from Hf lean in the initial stages of solidification to Hf rich in the later stages. In the unexposed samples the Hf lean (Ti,Ta)C carbide is the most numerous one. The shape of the complex MC carbide diffraction peaks are explained semi-quantitatively on the basis of the compositional range of the MC carbides.