Microsegregation in directionally solidified Ni-based superalloy

摘要

Development of directional solidification was motivated by an effort to control morphology of grain boundaries in order to improve fracture resistance. This technology was successfully applied to the production of columnar or single-crystal gas turbine blades made of superalloys or in-situ composites [1]. Directional solidification significantly improves the high temperature mechanical properties of superalloys. The solidification parameters (growth rate and temperature gradient) affect microstructural characteristics, i.e. morphology of dendrites or cells, morphology and distribution of precipitates, crystallographic texture, and micro-porosity. Previously published works [2, 3] on directionally solidified (DS) Ni-based superalloys showed that the temperature gradient in the melt at solid-liquid interface, GL, and growth rate, R, directly influence primary, λ{sub}1 and secondary, λ{sub}2, dendrite arm spacings and dendrite tip radius.