Chapter 3 – SUBSTRATE ALLOYS

Publisher Summary This chapter describes the temperature capability of metals and alloys. Metallic alloys are selected because of high melting point, strength, ductility and toughness, and low density wherever possible. The environmental resistance of the alloys is seldom adequate. High-temperature coatings are used extensively to protect the alloys from oxidation, corrosion, heat, and other processes of degradation. Solid-solution strengthening and precipitation hardening are effective at high temperatures and, therefore, are used in strengthening high-temperature alloys. Strengthening by solid solution and precipitation involves impeding motions of dislocations in the metallic structure. In a solid solution, appropriate alloying elements are dissolved in a metal. The solute atoms randomly substitute for the solvent atoms without altering the phase. Titanium alloys are very strong, and on a density-corrected basis, form some of the strongest alloys available. It is found that because of their high strength and low density, titanium alloys are extensively used in gas turbine engine as fan blades, compressor blades and vanes, disks, and cases. It is found that to achieve the optimum combination of microstructure, strength, and ductility of steels, heat treatment regimens have been developed using time temperature transformation diagrams.