Cobalt alloying element

Molybdenum, an unusually versatile alloying element, imparts numerous beneficial properties to irons and steels and to some alloy systems based on cobalt, nickel, or titanium. Comprehensive summaries of uses through 1948 (24) and 1980 (25) are available. 

Alloying elements either enlarge the austenite field or reduce it. The former include manganese, nickel, cobalt, copper, carbon, and nitrogen and are referred to as austenite stabilizers. 

The important (3-stabilizing alloying elements are the bcc elements vanadium, molybdenum, tantalum, and niobium of the P-isomorphous type and manganese, iron, chromium, cobalt, nickel, copper, and siUcon of the P-eutectoid type. The P eutectoid elements, arranged in order of increasing tendency to form compounds, are shown in Table 7. The elements copper, siUcon, nickel, and cobalt are termed active eutectoid formers because of a rapid decomposition of P to a and a compound. The other elements in Table 7 are sluggish in their eutectoid reactions and thus it is possible to avoid compound formation by careful control of heat treatment and composition. The relative P-stabilizing effects of these elements can be expressed in the form of a molybdenum equivalency. Mo (29) ... 

Mechanical properties depend on the alloying elements. Addition of carbon to the cobalt base metal is the most effective. The carbon forms various carbide phases with the cobalt and the other alloying elements (see Carbides). The presence of carbide particles is controlled in part by such alloying elements such as chromium, nickel, titanium, manganese, tungsten, and molybdenum that are added during melting. The distribution of the carbide particles is controlled by heat treatment of the solidified alloy. 

The composition of turbine blades is a complex mixture of alloying elements in solid solution in nickel. A typical alloy would contain Al, Cr, Mo, Co or Ta in amounts up to 10 atom per cent of the particular elements which are chosen. Of drese all except cobalt form substantially more stable oxides than... 

Approximately 90% of all RPDs are now cast from base metal alloys containing principally chromium, cobalt and nickel, with chromium being the element present in all such alloys. Commonly, these cast chromium alloys contain various alloying elements, typically <5% Mo, <1% Fe, 25-30% Cr and the balance Co although there are some widely used alloys containing... 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Other potential applications are ceramic powders coated with their sintering aids, zirconia coated withyttria stabilizer, tungsten carbide coated with cobalt, or nickel, alumina abrasive powders coated with a relatively brittle second phase such as MgAl204 and plasma spray powders without the segregation of alloying elements. 

Recent research on more coercive media with a low noise ratio involved addition of Zn to the Co alloy system [76-79]. Addition of Zn to the cobalt alloy very effectively produces a film with a fine particle structure, which results from codeposition of elements which are hardly soluble in the matrix. Such codeposition causes segregation and hence produces a film microstructure consisting of fine particles. The fine particulate structure lowers the noise ratio and increases the coercivity of the medium. 

An alloy is a substance that has metallic properties and is composed of two or more chemical elements, at least one of which is a metal. The elements composing the alloy are not distinguishable by the unaided eye. Examples of alloy coating include gold-copper-cadmium, zinc-cobalt, zinc-iron, zinc-nickle, brass (an alloy of copper and zinc), bronze (copper-tin), tin-zinc, tin-nickle, and tin-cobalt. Alloy coatings are produced by plating two metals from the same solution. 

Sectrodeposition of nickel and cobalt has been investigated intensively in aqueous solutions. Both metals are interesting for nanotechnology as magnetic nanostructures can be formed in aqueous solutions [47]. Hovrever, the bulk electrodeposition is accompanied by a massive hydrogen evolution. Both elements can also be deposited from acidic chloroaluminate liquids [48,49]. Cobalt and zinc-cobalt alloys... 

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. 

Alloy steel pipe composition has various elements, with total concentration between 1.0% and 50% by weight, which enhances the mechanical properties and corrosion resistance. These steels can be grouped under low-alloy steels. Along with economic growth, the demand of alloy steel pipes and tubes for industrial use has increased enormously. The most common alloying elements are nickel, chromium, silicon, vanadium, and molybdeniun. Special pipe steels also contain very small amounts of aluminum, cobalt, tungsten, titanium, and zirconium. Alloy steel has different properties on the basis of its composition. Alloy steel tubes cater to domestic and industrial requirements, such as gas drilling, offshore projects, refineries, and petrochemical plants. 

Small Cr contents increase the rate of reaction, but at 20% Cr, the reaction rate starts to decrease and exhibits a minimum value at 25%-30% Cr (Figure 20.62). The minimum value depends on the pressure. More chromium is needed to stabilize a protective film since the diffusion coefficient of chromium in cobalt is lower than for chromium in nickel. However, since the adhesion strength of the film on Co-Cr alloys is poorer than on Ni-Cr alloys despite the identical oxidation rate of the Cr-containing Co alloys with Cr203 protective film, the practical oxidation resistance is lower. Other alloying elements, as Figure 20.62 shows, have little influence on scale resistance. 

FIGURE 20.62 Influence of alloying elements on cobalt oxidation at 1000°C. 

At temperatures up to 417°C, cobalt has a hexagonal close packed (hep) structure, whereas above 417°C, it is face-centered cubic (fee). Alloying elements that are fee stabilizers (such as nickel, iron, and carbon) lower the transformation... 

Overall, this is the most significant use of cobalt, as shown in Table I (48% total use). Metallic cobalt is an important alloying element in numerous applications, such as super alloys (cobalt, nickel, iron based), magnetic alloys (soft, AlNiCo, SmCo), wear-resistant alloys, high speed steels, prosthetic alloys, and cemented carbide. 

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