ABSTRACT
The primary factors influencing material selection are service temperature, service stress, material cost, and component weight. In the low compressor stages, the operating temperature is lower and titanium (Ti) based alloys are used for disks, blades, and stators. Advanced aluminum (AI) alloys may also find applications at locations with lower operating temperatures. At the higher compressor stages, the operating temperature is increased to a point where the Ti-based alloys will no longer provide sufficient strength. Nickel (Ni) and nickel-iron (Ni-Fe) based superalloys are used at these higher temperatures. The temperature is the hottest in the combustor and turbine sections, which require Ni-based superalloys or cobalt (Co) based superalloys. The alloys must be resistant to environmental degradation (oxidation or hot corrosion) or they must be used in combination with an oxidation-and/or corrosion-resistant coating. Thermal barrier coatings are used to reduce the operating temperatures of the components. It is in these hotter environments that improvements in engine performance are achieved. Gas temperature at the entry to the turbine section is a parameter critical to the overall thermal efficiency of the engine. The higher the turbine inlet temperature, the better the efficiency, and this temperature is limited by the materials used in the turbine.
