Grain Selection during Directional Solidification of Aero-Engine Turbine Blades

The operating temperature of turbine blades in aero-engine engines has been demanded to increase for saving energy and increasing thrust. Turbine blades are made of nickel-base superalloys. Superalloys are a class of materials specifically developed for high temperature applications, particularly in the case of gas turbines for aero engines as well as land based power generation. Grain structure governs prolonged high temperature strength; this has formed the impetus both for alloy development as well as grain morphology, i.e. equiaxed directional - single crystal solidification. In this paper, the evolution of grain structure and the control of crystal orientation in gas turbine blades are presented. The conditions leading to the solidification of columnar grain and single crystal blades are analysed, and techniques for producing columnar grain and single crystal blades in industry are reported.