Directional Structures for Advanced Aircraft Turbine Blades

In order to achieve the performance and durability requirements of advanced gas turbine engines, highpressure turbine blade materials with directional structures will be required. Directional structures can be obtained by liquid-solid (solidification) or solid-solid (recrystallization) reactions, or by composite fabrication techniques. Currently, directional solidification is used to produce columnar-grained superalloy turbine airfoils. This production process can be modified to provide single-crystal superalloys or directionally solidified eutectic turbine blades. Directional superalloy structures also can be obtained by a solid-state recrystallization process, referred to as directional recrystallization. In addition, directional composite structures are fabricated by reinforcing a superalloy matrix with high-strength refractory metal wires. These five directional turbine blade materials are compared for use in advanced gas turbine aircraft engines. The present status of each advanced material is reviewed, and the advantages and limitations of each is assessed.