Effect of withdrawal rate on precipitation characteristics of MC-type carbides in a nickel-based directionally solidified superalloy with high Re content

The precipitation characteristics of MC-type carbides during directional solidification of a rhenium-containing nickel-based superalloy were investigated at different withdrawal rates ranging from 50 to 200 μm/s. The results indicate that the carbides are located in the interdendrite, which includes the intergranular and intragranular regions. With increasing in withdrawal rates, the area of intergranular region decreases and the area of intragranular region increases. At lower withdrawal rate of 50 μm/s, the carbides are mainly located on the grain boundaries. However, an increase in the withdrawal rate promotes carbide from the intergranular region to the intragranular region, this is attributed to a rise in the withdrawal rate, which decreases the area of intergranular region and increases the area of intragranular region. When the withdrawal rates increase from 50 to 200 μm/s, the total number of carbides in the intergranular and intragranular regions increases. The morphologies of the carbides in the intergranular region are mostly blocky, sheet-like, rod-like and coarse Chinese script-shaped after a deeply-etched treatment, whereas the carbides in the intragranular region are primarily sheet-like, rod-like, and fine Chinese script-shaped. Further, it is suggested that rhenium is not the forming element of MC-type carbide in the superalloy with rhenium.