Abstract
The single crystal superalloys CMSX-4 and TMS75 were tested for very long times at high temperatures in laboratory creep tests and in service. The microstructure was investigated in TEM and SEM. It was found, that the ’-phase is cut at stresses much below the threshold given in literature. Cutting takes place by <110> screw dislocations. These mobile dislocations can be locked locally by a Giamei-lock. Thus a stacking fault dipole forms between the locked segment and the preceding ones. The dipole consists of two supershockley dislocations with 30° character, which are also stabilized by Giamei locks. The dipole formation is analyzed and discussed in detail.
Highlights
Nickelbase superalloys are applied for blades in turbines
The single crystal superalloys CMSX-4 and TMS75 were tested for very long times at high temperatures in laboratory creep tests and in service
The dipole consists of two supershockley dislocations with 30° character, which are stabilized by Giamei locks
Summary
Nickelbase superalloys are applied for blades in turbines. Such blades were first used in military engines, in civil aircrafts and in stationary turbines. Laboratory investigations are mostly performed in the several hundreds hour range, which is about a factor of 10 below realistic conditions. It is well known, that the microstructure of superalloys is not stable during high temperature creep: the cubical γ’precipitates coalesce and grow [1], dislocations relax coherency stresses and generate internal stresses on their part [2]. Cutting of the precipitates becomes necessarily the step and the topic of the paper is dislocation movement in the γ’-phase of technical alloys under service conditions
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