Influence of solution temperature on microstructure and creep property of a directional solidified nickel-based superalloy at intermediate temperatures

Abstract

By means of solution treatment at different temperatures, creep properties measurements and microstructure observations, an investigation has been made into the influence of solution temperature on the elements segregation and creep behaviors of a directionally solidified nickel-based superalloy at intermediate temperatures. Results show that after solution treated at 1230°C, the bigger composition segregation and un-homogeneous microstructure exist still in the dendrite/inter-dendrite regions of the alloy. The fine γ′ precipitates are distributed in the dendrite arm regions, while the coarse ones are distributed in the inter-dendrite regions. After solution treated at 1260°C, the segregation extent of the elements reduces obvious and the fine γ′ precipitates distribute homogeneously in the dendrite/inter-dendrite regions. Moreover, the particle-like carbides are precipitated along boundaries, which may restrain boundary slipping. The deformation mechanism of alloy during creep at intermediate temperature is dislocations slipping in matrix and shearing γ′ phase; the super-dislocations shearing into γ′ phase may cross-slip from {111} plane to (100) plane to form the configuration of K–W locking, which can hinder dislocation slipping on {111} plane. In the latter stage of creep, the cracks may be initiated and propagated along the boundaries with different angles relative to the stress axis. The fact that the boundaries at about 45° angles relative to the stress axis bear the maximum shearing stress increases the probability of the cracks initiating and propagating along the boundaries.