Gas Turbine Materials Requirement and Selection
- Gas turbine power plants are designed to achieve high output and efficiency. To achieve this objective, these plants have to operate at high temperatures.
- Unlike diesel power plants, the components of a gas turbine power plant are exposed continuously to these high temperatures.
- Apart from this the blades of compressor and turbine are subjected to high centrifugal stresses owing to their high speeds, thus materials for blades needs to be designed for high strength to withstand high centrifugal and thermal stresses and creep with proper cooling of blades. Therefore, the blade materials must possess the following properties :
- To withstand high temperatures and high thermal stresses.
- High resistance to crrosion, corrosion and oxidation.
- Should have low creep rate to avoid lengthening of blades.
- Should not behave like plastic materials at high temperatures.
- High resistance to fatigue failure.
- Components must be weldable and castable.
- Turbine rotors are made of Austenitic steels with 12% to 18% chromium, 8 % to 12 % Nickel and small percentages of titanium, molybdenum and tungsten. Blade materials are Nickel-Chromium based materials.
- It uses stainless steel alloys and 8-20 nickel chromium alloys known as Nimonic alloys. These materials meet the required properties outlined above.
- A uniform coating with ceramics like silicon carbide or silicon nitride on blades provides better mechanical strength and capability to withstand temperatures over 1500°C.
- Nickel alloys have high strength and these can withstand higher temperatures when cast rather in forged form.