Carbide behaviour during high temperature low cycle fatigue in a cobalt-base superalloy

摘要

The carbide behaviour of a directionally solidifiedcobalt-base superalloy has been investigated after low cyclefatigue at 900℃. During fatigue, primary carbides, M7C3 andMC, decomposed sluggishly and a great amount of secondarycarbide, chromium-rich M23C6 precipitated. The inhomogeneousdistribution of M23C6 brought about a different dislocationsubstructure. In the vicinity of the primary carbides, densely-distributed fine M23C6 pinned up dislocations effectively,resulting in a uniform distribution of dislocations, while in theinterior of grains, since precipitates were coarse and scarce,dislocations were arranged in a planar array and piled up in thefront of the precipitates. M23C6 also acted as an obstacledeflecting fatigue crack.