CHAPTER LIST

11.1 INTRODUCTION

Among the many different technologies that have made possible the development and operation of gas turbines at very high temperatures, superalloys stand at the forefront. The alloys used in the manufacture of jet engines and industrial and marine gas turbines represent the leading edge in materials, and in turn these engines have been the primary driving force for the development of superalloys. Rocket engines, nuclear reactors, submarines, steam power plants, and space vehicles also extensively use superalloys.

Turbine inlet temperatures have gone up by nearly 450 C in the last 30 years. Approximately 70 percent of this increase has been gained from improved design of cooling of blades and vanes by taking advantage of serpentine passages, turbulators, pin fins, film cooling, and thermal barrier coatings (TBC). The remaining 30 percent gain in inlet temperature is derived from improved superalloys and casting processes. Significant advances in metal temperature, stress, and environmental capabilities for turbine airfoils have been obtained from the development of directionally solidified, columnar grain and single-crystal casting processes. Casting and solution heat treatment of directionally solidified materials is less expensive, and the production of single and multiairfoil vane segments with a large platform is not complex.

Ever since man constructed mechanical devices, it has been observed that the efficiency in performing useful work is related to making use of high temperatures. With the development of the thermodynamic Brayton cycle (in conjunction with decreased rejection temperature), the basic...