Why Power Generation Needs Nickel Superalloys for High-Temperature Performance

Increasing the efficiency of power generation is really about increasing temperatures. Whether the task is to supply electricity to the national grid or provide process steam to industries, the basic thermodynamic rule applies – the higher the temperature of the working fluid, the more energy will be obtained from the unit of fuel. Over many years of research and practical application, the search for high-temperature materials has been the main trend in materials science. It explains the widespread use of nickel superalloys in the power generation industry.

The Temperature Challenge

In modern gas turbine engines used in power generation, inlet temperature can reach 1,400°C. At the same time, there are significant stresses in the form of rotation, oxidation of the material, cyclic temperature changes during startup and shutdown of the engine. An alloy, having excellent characteristics at room temperature, may behave completely differently when rotating at thousands of RPMs under the influence of combustion gases.

Steel starts losing its strength properties at temperatures above 550°C. Alloys based on aluminium are also limited in terms of the upper temperature limit. Nickels superalloys, on the other hand, were specifically designed to function where other alloys are failing.

The Advantages of Using Nickel

Nickel's face-centered cubic crystal lattice gives it good thermal stability. Phase transformations do not take place in the structure of ferritic steel at elevated temperatures, making nickel superalloys resistant to high temperatures. Thermal stability is the basis of everything.

But the main thing that makes nickel superalloys unique lies in their alloying composition. Adding chromium, cobalt, aluminium, titanium, and molybdenum to a certain degree gives rise to a special strengthening phase called gamma prime (γ'), which includes the ordered precipitation of nickel, aluminum, and titanium. And what is special is that this strengthening phase is resistant to temperature increases, which means that these materials retain their characteristics at high temperatures, unlike other alloys.

Resisting Creep, Oxidation, and Hot Corrosion

The resistance to high temperatures is only one half of the question. Materials for gas turbine engines should also be capable of resisting creep – gradual deformation under constant temperature and stress. For components like blades and vanes, which work continuously for thousands of hours, it is a critical property. Single crystalline or directionally solidified nickel superalloys belong to the category of highly creep-resistant alloys.

Then there are chemical conditions. Hot combustion gases include sulphur-containing compounds and water vapor, which actively corrode the surface of materials. The presence of chromium in the composition of nickel superalloys results in the formation of chromia layer, which serves as a barrier against further oxidation and hot corrosion. If necessary, additional thermal barrier and aluminide coating can be applied to the substrate of the nickel alloy.

Growing Demand

With the energy transition in progress, new challenges arise for materials selection. Hydrogen combustion trials in gas turbine engines are becoming more common to reduce carbon footprint. Hydrogen is giving off more heat and is more oxidizing than natural gas. This means that there is an additional challenge to the components' materials, and much of the ongoing development efforts by the turbine manufacturers are focused precisely on nickel superalloys capable of surviving in such conditions.

On top of that, operators want to extend maintenance intervals and increase output, putting additional strain on the materials.

Choosing Specifications

For engineering and procurement specialists, understanding the difference between different specifications of nickel superalloys – be it Inconel 718, Waspaloy, or any Rene alloy – is very important. They differ in properties, cost, and fabricability and can affect the service life of turbine components.

Dynamic Metals offers a variety of grades of nickel superalloys suitable for power generation applications. If you have a specific material specification or need help with choosing one, our technical specialists will be happy to assist.