Nickel-iron-cobalt-base superalloys

Addition of rare earths improves the high temperature oxidation resistance of heat-resistant alloys. The improved resistance is observed in terms of reduction in weight gain and 

The presence of Y in the coatings improves the oxidation resistance of AI2O3 scale. Thus, MCrAlY coatings outperform diffusion aluminides significantly in oxidation tasks as shown in Table 12.8. 

Microalloying of Ni-base alloys with rare earths improves ductility, stress rupture life and creep resistance as shown in Table 12.9. The improved properties are due to desulphurisation caused by rare earths. Addition of cerium to inconel 600 and Hstalloy improves their hot workability. 

These are potentially useful high-temperature materials. Chromium is moderately resistant to oxidation but absorbs nitrogen from air and loses structural stability. Addition of 

MODERN ASPECTS OF RARE EARTHS AND THEIR COMPLEXES 

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The arrangement of the melting and vacuum spray chambers is critical for guiding the liquid metal to eject into the vacuum chamber. Difficulties exist in precisely controlling the expulsion of the liquid metal into the vacuum chamber. Therefore, flaky droplets may be formed in vacuum atomization. Although vacuum atomization was developed mainly for the production of high-purity nickel and cobalt based superalloy powders, it is also applied to atomize the alloys of aluminum, copper and iron. 

High-purity metals and superalloys are required for the aeronautics, electronics, instruments, space, and defense industries the raw materials are at present imported. Primarily, these special metals include nickel-and cobalt-based superalloys, high-strength iron-based alloys, titanium-based alloys, controlled-expansion alloys, and magnetic materials. Keeping in view the importance of these metals and alloys and the expertise available in India for making them, the NCST has identified two projects for their development the setting up of a special metal and superalloys plant and the development of controlled-expansion alloys. 

Superalloys ate complex alloys containing up to 16 and more elements. There exist three basic types iron, nickel, and cobalt base alloys. Their important properties are ... 

Nickel based superalloys are one of three groups of materials used for demanding, high-temperature applications such as jet engines and gas turbines (e.g., Inconel X-750). The other two groups are iron-based and cobalt-based superalloys. 

The term superalloy is used for a group of nickel-, iron-nickel-, and cobalt-based high-temperature materials for applications at temperatures > 540 °C. It is useful to compare the main subgroups in terms of the strengthening mechanisms applied and stress-rupture characteristics achieved, as shown in Fig. 3.1-127. In this section iron-nickel- and nickel-based superalloys are covered whereas cobalt-based superalloys are dealt with in Sect. 3.1.6.3. Nickel-based superalloys are among the most complex metallic materials with numerous alloying elements serving particular functions, as briefly outlined here. 

Iron-, nickel-, and cobalt-based alloys used primarily for high-temperature applications are known as superalloys. The iron-based grades, which are less expensive than cobalt- or nickel-based grades, are of three types ... 

Superalloys are alloys that display a particularly excellent ability to resist deformation under stress at high temperatures along with good resistance to corrosion and great surface stability. Most often, a superalloy involves nickel, cobalt, or nickel-iron as the base alloying element. Superalloys have been used primarily in turbines and in the aerospace industry. 

Hastelloy X (HastX) is a nickel-based superalloy used in a variety of applications [Brown, 1992]. Its composition is 49% nickel, 22% chromium, 18% iron, 9% molybdenum, 1.5% cobalt and 0.5% tungsten. The melting point of HastX is about 1530 K, and it has a density of 8.22 g/cc. This material has been suggested as a possible reactor material for a variety of reasons. HastX is a material with decent high temperature characteristics. Hastelloy is also noted for excellent corrosion, oxidation and carburization resistance at the desired temperatures. Finally, Hastelloy-X is a commonly used metal whose properties are well understood. The expected peak temperature of Hastelloy-X is roughly 875 K when used for the pressure vessel of the reactor. 

The nickel-based alloys are sometimes referred as superalloys. They have been defined as those possessing good high-temperature strength and oxidation resistance and are alloys of nickel, cobalt, and iron that contain... 

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