High-temperature Alloys in Relation to Gas-turbine Design

In order to achieve a thermal efficiency in the gas turbine comparable with that realized in steam practice, a higher turbine-entry temperature is necessary. Limiting discussion to the combustion and expansion sections of the gas turbine, the paper first indicates that the use of metals in high temperature and stress conditions necessitates a new approach to component design. The phenomena of creep and fatigue assume major importance whilst pure temperature effects, such as expansion and thermal shock, are additional problems. These properties are defined and an indication is given of their significance in the design of combustion chambers, turbine wheels, and blades. Susceptibility to heat treatment, intended to induce the desired high-temperature properties, is another important factor to be considered in material selection, as are fabrication characteristics. Since the latter govern both detail and general design, the merits of forging, casting, and welding are outlined when applied to high-temperature alloys. The paper concludes with a survey of the problems likely to be encountered with future materials, particularly ceramics, whilst suggesting that increased efficiency may be obtained by further research on established alloys or by design innovations such as cooling.