BOOK_CONTENT
From Mechanical Alloying: Fundamentals and Applications

1.1 HISTORY

The use of inert additions to improve elevated temperature mechanical properties of metals was first exploited in 1910 by W.D. Coolidge in thoriated tungsten [1]. The development of dispersion-strengthened alloys by internal oxidation started in 1930 [2] and the invention of dispersion-strengthened aluminium took place in 1949 [3]. However, the relatively low melting point of aluminium was a severe limitation for the use of SAP at elevated temperatures. This led to attempts in applying dispersion strengthening to higher melting point metals such as copper and nickel.

In these metals, the self oxides cannot be used as they are not sufficiently stable against Ostwald ripening at elevated temperatures. ThO 2-dispersed nickel, having a finely distributed dispersoid, was produced successfully by melting to improve the mechanical properties (1960) [4]. The material has vastly developed elevated temperature properties. However, the use of such materials was still limited due to their low strength at intermediate temperatures and lack of corrosion resistance.

Hypothetically, these shortcomings could be solved by combining the corrosion resistance and intermediate temperature strength of ?'-precipitation-hardened, nickel-base superalloys with the high temperature strength and stability of oxide dispersion strengthening. One of the primary hurdles to materialize this idea is the production of uniform dispersion of fine oxide particles, less than 0.1 ?m in size, in alloy powder particles in such a manner which leads to interparticle spacing of less than 0.5 ?m in a consolidated product. The nickel-base superalloys contain chromium, aluminium and titanium for effective...

Copyright P.R. Soni 2001 under license agreement with Books24x7

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Superalloys
Superalloys are nickel, cobalt or iron-based alloys with excellent elevated temperature strength, creep properties and oxidation resistance.
Ferrous Metals and Iron Alloys
Ferrous metals and alloys are iron-based materials that are used in a wide variety of industrial applications.
Nickel and Nickel Alloys
Nickel and nickel alloys are non-ferrous metals with high strength and toughness, excellent corrosion resistance, and superior elevated temperature properties.
Refractory and Reactive Metals
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear and have extremely high melting points. Reactive metals have a strong affinity for oxygen and nitrogen at elevated temperatures and are highly resistant to corrosion at low temperatures.
Precious Metals and Alloys
Precious metals and precious alloys are rare metallic elements and alloys such as silver, gold, platinum, palladium, iridium, osmium, rhodium, and ruthenium. They posses unique characteristics that set them apart from other metals.

Topics of Interest

2.1 ALLOYING MILLS A variety of milling equipment such as attritor mills, vibratory mills, high speed blenders and shakers, planetary mill, and even large diameter conventional ball mills have been...

Overview Superalloys are heat resistant alloys of nickel, iron nickel and cobalt that frequently operate at temperatures exceeding 1000 F. However, some superalloys are capable of being used in load...

12.3 ALUMINIUM-BASE MATERIALS The MA process can be applied to aluminium-base systems provided that organic process control agents are used to control the extreme tendency of aluminium to weld to...

Since its advent, the MA technique has been applied to develop various novel compositions and improve the performance of existing materials. Many of these are produced at industrial level and find...

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...