Fatigue and Oxidation of High-Temperature Alloys -USSR-
JOINT INTELLIGENCE OBJECTIVES AGENCY WASHINGTON DC
Pagination or Media Count:
Nozzle vanes of gas turbines operate under conditions of an unsteady temperature field. Thermal stresses forming during engine starts and stops lead to premature fracture of vanes due to the onset and development of thermal fatigue cracks. In a number of works the decisive role of surface layers of heat-resisting alloys in opposing fracture at high temperatures and under conditions of unsteady heating is presented. it has also been established that cracks which form in the surface layers of intake vanes and sometimes in the discharge vanes are developed in grain boundaries. However, due to difficulties of an experimental nature insignificant thickness of surface layers, until recently there was no systematic data on the effect of thermal cycling on phase composition and structure of surface layers of vanes under operating conditions. The present investigation is devoted to a study of the structure changes in surface layers and internal regions of samples and vanes of cast nimonic.
- Metallurgy and Metallography