Effect of Withdrawal Rate on Microstructure and Mechanical Properties of a Third Generation Nickel Based Single Crystal Superalloy

The influence of withdrawal rate (3, 4.5,6,9 and 12 mm/ min) on microstructure and high temperature rupture properties of A3 alloy was investigated by testing the microstructure and properties of the third generation nickel-based single crystal superalloy. The results show that with the increase of withdrawal rate, the dendrite spacing decreased exponentially, the segregation degree of main elements and the content of (γ + γ) eutectic structure decreased, and the size of γ phase decreased. After heat treatment, the eutectic structure was dissolved basically, and the segregation of the forming elements of γ phase is eliminated at different withdrawal rates. The size of γ phase in dendrite is smallest of 372.3μm at 4.5 mm/ min, the pore content is significantly larger than that of as-cast alloy, and decreased firstly and then increased with the increasing of withdrawal rate, which is 0.112% at 4.5 mm/ min and 0.182% at 3 mm/ min. The rupture life of the alloy at 1100 °C/140MPa is the longest at 4.5 mm/ min, which is mainly determined by the precipitation of TCP phase, pore content and γ size.