Abstract:

The temperature gradient and the growth rate are the two main parameters of a directional solidification process, which may be expressed synthetically as the cooling rate. In this paper, various directional solidification techniques have been used in the research of dendritic segregation of a cobalt-base superalloy during directional solidification with the cooling rate between 10-2-102K/s. Results show that the increase of cooling rate can restrain dendritic segregation effectively, especially for easily segregated alloy elements. Two mechanisms are favourable in the restraint of dendritic segregation: one is the microstructure refinement by increasing cooling rate, another is non-equilibrium partitioning of solutes at the solid/liquid interface which makes the partitioning coefficient tend to unity.

Key words: directional solidification, cooling rate, superalloy, dendritic segregation