Effect of heating processing on the formation of micro-pores during solution treatment of high generation nickel-based single crystal superalloy

With the development of nickel-based single crystal superalloys, the quantity of micro-pores generating in solution treatment has increased, and there is an urgent need to develop a solution treatment design method that takes account of both residual eutectics and micro-pores. Therefore, the effect of heating processing on the formation of micro-pores during solution treatment of a 4th generation nickel-based single crystal superalloy has been investigated using high-resolution transmission X-ray tomography and electron probe microscopic analyzer. In the temperature range below interdendritic γ' phases solvus, decreasing the heating rate can limit the formation of micro-pores significantly. However, heating method (continuous or stepwise), has a little effect on micro-pores formation. The influence of heating processing on micro-pores formation is associated with composition homogenization degree of the alloy before eutectics dissolve. Moreover, it is found that the dissolution of eutectics is most likely the reason for substantial formation of micro-pores. Finally, a designing thinking for heating processing of solution treatment for high generation nickel-based single crystal superalloys is proposed.