Materials for Gas Turbines – An Overview

Abstract

Advancements made in the field of materials have contributed in a major way in building gas turbine engines with higher power ratings and efficiency levels. Improvements in design of the gas turbine engines over the years have importantly been due to development of materials with enhanced performance levels. Gas turbines have been widely utilized in aircraft engines as well as for land based applications importantly for power generation. Advancements in gas turbine materials have always played a prime role – higher the capability of the materials to withstand elevated temperature service, more the engine efficiency; materials with high elevated temperature strength to weight ratio help in weight reduction. A wide spectrum of high performance materials special steels, titanium alloys and superalloys is used for construction of gas turbines. Manufacture of these materials often involves advanced processing techniques. Other material groups like ceramics, composites and inter-metallics have been the focus of intense research and development; aim is to exploit the superior features of these materials for improving the performance of gas turbine engines. The materials developed at the first instance for gas turbine engine applications had high temperature tensile strength as the prime requirement. This requirement quickly changed as operating temperatures rose. Stress rupture life and then creep properties became important. In the subsequent years of development, low cycle fatigue (LCF) life became another important parameter. Many of the components in the aero engines are subjected to fatigueand /or creep-loading, and the choice of material is then based on the capability of the material to withstand such loads. Coating technology has become an integral part of manufacture of gas turbine engine components operating at high temperatures, as this is the only way a combination of high level of mechanical properties and excellent resistance to oxidation / hot corrosion resistance could be achieved. The review brings out a detailed analysis of the advanced materials and processes that have come to stay in the production of various components in gas turbine engines. While there are thousands of components that go into a gas turbine engine, the emphasis here has been on the main components, which are critical to the performance of the engine. The review also takes stock of the R&D activity currently in progress to develop higher performance materials for gas turbine engine application. On design aspects of gas turbine engines, the reader is referred to the latest edition of the Gas Turbine Engineering Handbook (Boyce, 2006).