The Role of Materials in Enabling Gas Turbine Technologies

Abstract

Abstract Materials used in high-temperature structures have design constraints in additional to those materials used at or near room temperature. Three important constraints are time-dependent inelastic strain (creep), thermal stability of microstructure, and high-temperature oxidation and/or corrosion. The U.S. Navy employs gas turbine engines for aero-propulsion and for propulsion and auxiliary power for select surface ships. For modern aircraft gas turbines, combustion gas temperatures up to 2100°C and alloy temperatures as high as 1150°C is possible. This is well above the melting point of most alloys, so film cooling of the combustion chamber is necessary. Materials (nickel-base superalloys, ceramic matrix composites (CMCs), refractory alloys, overlay, diffusion, and thermal barrier- and environmental barrier coatings) in commercial, marine and aero gas turbine engines must be able to withstand a variety of aggressive, harsh operating conditions. Current gas turbine engines employ the Brayton cycle where overall turbine efficiencies increase as the engine temperatures increase. Predicting corrosion of metals, alloys, or coated alloys is often difficult because of the variable operational demands placed on Predicting corrosion of metals, alloys, or coated alloys is often difficult because of the variable operational demands placed on a given power system, and the variable composition of the corrosive environment. Prediction is further complicated because materials often degrade in a high-temperature environment by more than a single corrosion mechanism. Research is underway to use other cycles such as the Atkinson or Humphrey Cycles that hold the promise of improved efficiency when applied to gas turbine type machinery. A rotating detonation engine (RDE) is an engine is an engine using a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. In detonative combustion, the flame front expands at supersonic speed. It is theoretically more efficient than conventional deflagrative combustion by as much as 25%. That would translate to major fuel savings. During the combustion very high temperatures (3000–4000K) and pressure (1–100 bar) levels are attained through the combustor. Although RDE research is continuing to establish combustion stability and reduce noise, materials will need to be developed or applied to promote long term performance. These materials will need to endure temperature spacial inhomogenieties and fluctuations, pressure cycling, and harsh environmental operational conditions.