Abstract: The features of microstructure and their influence on mechanical properties on stress-rupture as well as thermal fatigue of directionally solidified DZ38G nickel-base su- peralloy have been investigated.It has been found that the contents of carbides on grain boundaries are increased and morphology of γ'- precipitates has been changed after testing. Particularly γ'-precipitates coalesced into raft-like in morphology perpendicular to the applied stress-axis have been observed that has no detrimental effect on the stress-rupture behaviour.The tendency of σ-formation has also been discussed.The σ-phase can be avoided when the process parameters are chosen appropriately during solidification.

Key words: superalloy, microstructure, directional solidification, crack propagation, segregation