Improvement technologies of gas turbine super alloys

Identification of the material’s creep strength is essential for gas turbine engines, evaluation of age hardening, creep and gamma prime volume fraction and constantly increasing service temperature needs for aircraft engines resulted in the production of wrought alloys with increasing magnitudes f aluminum and titanium. Component forgeability issues resulted to this direction of development not crossing the specific level. The chemistry of wrought alloys is limited by hot working factors. This condition resulted into the development of cast nickel-base alloys. Casting compositions can be adjusted for sufficient high temperature strength because of no need of forgeability. Additionally the cast components are intrinsically stronger than forging at the elevated temperatures because of coarse grain size of castings.

Rotating airfoils should withstand vigorous combination of temperature, stress and environment. The bucket is generally loaded and is the limiting factor of gas turbine. Performance of nozzles is to direct the hot gases towards the bucket. So, they should be able to withstand high temperatures. Although they are subjected to lower mechanical stresses as compare to buckets. An essential design need for the nozzle materials is that they should have supreme high temperature oxidation and corrosion resistance.

Nickel based alloys Inconel bar are the materials chosen for the demanding gas turbine applications.  These alloys offer excellent combination of high temperature strength and hot corrosion resistance which makes them perfect for heavy duty gas turbine applications. Enhancements in processing technology have enabled development of the alloy in large ingot sizes. The alloys are used in the whole heavy duty gas turbine industry.

Air craft engines

A wide failure mechanism for gas turbine airfoils included nucleation and growth of cavities around transverse grain boundaries. Prevention of transverse grain boundaries through direction solidification of turbine blades and vanes made an essential step in temperature potential of the castings. Using directional solidified nickel based super alloys can enhance the turbine blade metal temperature potential by around 14oC relative to the conventionally cast super alloys.

Using directionally solidified super alloys can enhance the turbine blade temperature potential by 14oC relative to the conventionally cast super alloys. They offer long term creep rupture strength and hot corrosion resistance. The alloys can be directionally solidified in the form of large hollow blades.

Single crystals

In single  crystal castings, whole grain boundaries are discarded from the microstructure and a SC with a controlled orientation is developed in an airfoil shape. The castings needed no grain boundary strengtheners like Carbon, Boron, Zirconium and Hafnium. Discarding thee elements while designing the single crystal compositions improve the melting point and overall the high temperature strength. The single crystal alloys offer around 20oC metal temperature benefit over the standard directional solidified alloys. Chances to further enhance the metal temperature of these materials by increasing the magnitude of refractory elements resulted into the development of SC super alloys that offered improvement by 30oC metal temperature as compare to traditional SC alloys.