Chemical Development
Creep resistance is dependent on slowing the speed of dislocations within the crystal structure. In Ni-base superalloys the gamma prime phase present acts as a coherent barrier to dislocation motion and is a precipitate strengthener. Chemical additions such as aluminum and titanium promote the creation of the gamma prime phase. The gamma prime phase size can be precisely controlled by careful precipitation hardening heat treatments. Many superalloys are produced using a two-phase heat treatment that creates a dispersion of square gamma prime particles known as the primary phase, with a fine dispersion between these known as secondary gamma prime. Many other elements, both common and exotic, (including not only metals, but also metalloids and nonmetals) can be present; chromium, cobalt, molybdenum, tungsten, tantalum, aluminium, titanium, zirconium, niobium, rhenium, carbon, boron or hafnium are just a few examples. Cobalt base superalloys do not have a strengthening secondary phase like gamma prime.
Read more about this topic: Superalloy
Famous quotes containing the words chemical and/or development:
“We do not want actions, but men; not a chemical drop of water, but rain; the spirit that sheds and showers actions, countless, endless actions.”
—Ralph Waldo Emerson (1803–1882)
“This was the Eastham famous of late years for its camp- meetings, held in a grove near by, to which thousands flock from all parts of the Bay. We conjectured that the reason for the perhaps unusual, if not unhealthful development of the religious sentiment here, was the fact that a large portion of the population are women whose husbands and sons are either abroad on the sea, or else drowned, and there is nobody but they and the ministers left behind.”
—Henry David Thoreau (1817–1862)