Effect of Hf on carbides of FGH4096 superalloy produced by hot isostatic pressing

FGH4096 alloys with Hf contents of 0, 0.3 and 0.6 wt% were studied to clarify the effect of Hf on the carbides in these alloys. The carbides in FGH4096 alloys produced on HIPing and during high temperature tensile deformation were analyzed by SEM, TEM and EDS. The results indicated that carbides in HIPed alloys were mainly blocky MC and the previous particle boundaries (PPB) in the alloys were decorated by the carbides. ZrO2 cores with a cubic lattice were observed in part of the MC distributed at the PPB (PPB MC), while part of PPB MC in Hf modified alloys had an orthorhombic HfO2 core. Volume fraction of MC increases with increasing Hf content of the alloys. The formation of PPB MC was suppressed in the alloy with 0.3 wt% Hf, but more MC precipitated at the PPB when Hf content of the alloy was raised to 0.6 wt%. The amount of M23C6 delineations that precipitated at grain boundaries during aging treatment decreased with increasing Hf content. Besides, the formation of a film-like M23C6 at grain boundaries during tensile deformations at 650 °C and 750 °C were suppressed in the Hf modified alloys, which contributed a lot to the improvement of the tensile properties of FGH4096 alloys at elevated temperatures.