Challenges and underlying causes associated with the hot deformation of as-cast GH4975 superalloy

In this study, the challenges and underlying causes associated with the hot deformation of the as-cast GH4975 superalloy are analyzed in detail. The findings reveal that the primary difficulties involve excessive deformation resistance, severe deformation cracking, and insufficient dynamic recrystallization (DRX). The excessive deformation resistance is primarily attributed to the finely dispersed γ ′ strengthening phase, which hinders the movement of dislocations and grain boundaries. Although the solid solution strengthening effect of solute elements contributes to this resistance, it is not the principal factor. Deformation cracking in the γ/γ ′ coexistence region is mainly due to the local stress concentration arising from the non-uniform γ ′ phase, as well as the large-sized (γ+γ ′ ) eutectic phase and MC carbide. Nonmetallic inclusions such as Al 2 O 3 , MgO·Al 2 O 3 , and TiN can serve as heterogeneous nucleation sites, leading to an increase in the size of MC carbide and exacerbating cracking. Deformation cracking in the γ single-phase region is primarily due to the liquefaction of the low melting point (γ+γ ′ ) eutectic phase. The insufficient DRX can be attributed, on one hand, to the excessively large initial grain size (an average width of approximately 0.38 mm and an average length exceeding 3 mm), which limits the nucleation and development of DRX grains near the boundaries. On the other hand, it can be attributed to the finely dispersed γ ′ phase, whose ratio of the volume fraction to the average equivalent radius ( f v / r ) far exceeds the critical threshold of 0.2 μm −1 , effectively suppressing DRX development.