Alloying cobalt-based alloys

Element Nickel base alloys Cobalt base alloys ... 

Use of CRA is competitive with inhibition in deep, high-pressure wells, particularly in those locations where inhibitor supply may be a space and logistic problem. CRA includes stainless steels (austenitic, ferritic, martensitic, and duplex), nickel-based alloys, cobalt-based alloys, and titanium alloys. Economics is a major factor in alloy selection. The 13 Cr tubing has often been used in gas wells for low H2S wells. Tubing materials selection for a deep well could involve price increments between alloys of 1 to 3 million. High-strength CRA is used to minimize costs. SMYS values of 150 ksi (1000 MPa) are common. The CRA is often cold-worked to achieve the required yield strength. 

Weld hardfacing coatings, for example, high-carbon iron-chromium alloys, tool steels, nickel-chromium-boron alloys, cobalt-base alloys, and austenitic manganese steels... 

Aluminum Alloys Beryllium Copper Alloy Cobalt-Base Alloys Copper and Cop r Alloys Lead and Lead Alloys Nickel and High-Nickel Alloys Zinc Alloy... 

Titanium and its alloys are known as being the most suitable metalUc biomaterials. They are used in orthopaedic applications due to their excellent mechanical properties. More importantly, they form a very stable oxide layer in body fluid and hence possess exceptional biocompatibility as compared with other metal implant materials. However, these materials undergo failure due to siuface reactions and mechanical loading. Passive corrosion or accelerating processes snch as wear have led to the release of titanium and the other alloying elements into the surrounding tissues. This section discusses the corrosion issues in titanium and its alloys, cobalt-based alloys, stainless steels and nickel-titanium alloys. 

Density is a particularly important characteristic of alloys used in rotating machinery, because centrifugal stresses increase with density. Densities of the various metals in Table 1 range from 6.1 to 19.3 g/cm. Those of iron, nickel, and cobalt-base superaHoys fall in the range 7-8.5 g/cm. Those alloys which contain the heavier elements, ie, molybdenum, tantalum, or tungsten, have correspondingly high densities. 

Tables 10 and 11 list typical compositions of cast and wrought cobalt-base alloys, respectively. Stress—mpture properties of two wrought cobalt alloys, Haynes 188 and L-605, are compared to those of iron—nickel alloys ia Figure 10 (49). The cobalt alloys generally are inferior ia strength to the strongest cast nickel-base superaHoys. Tensile strengths at low and iatermediate temperatures are particularly deficient for the cobalt alloys.

Table 10. Compositions of Wrought Cobalt-Base Alloys, wt %...

The cobalt deposition rate on new, replacement, or decontaminated recirculation piping surface has been reduced by pretreating the piping using an atmosphere of oxygenated wet steam to form an oxide film (25). Studies have been conducted for both PWRs and BWRs to reduce the cobalt content of materials used in the nuclear parts of the plants, particularly in hardened and wear surfaces where cobalt-base alloys ( 50% Co) are used (26). Some low cobalt materials have been developed however, the use of the materials is limited to replacement parts or new plants. 

Titanium alloy systems have been extensively studied. A single company evaluated over 3000 compositions in eight years (Rem-Cm sponsored work at BatteUe Memorial Institute). AHoy development has been aimed at elevated-temperature aerospace appHcations, strength for stmctural appHcations, biocompatibiHty, and corrosion resistance. The original effort has been in aerospace appHcations to replace nickel- and cobalt-base alloys in the 250—600°C range. The useful strength and corrosion-resistance temperature limit is ca 550°C. 

Cr C Cr C chromium iton(l l) [12052-89-0] CrFe (c phase), and chromium iron molybdenum(12 36 10) [12053-58-6] Cr 2F 36 o Q phase), are found as constituents in many alloy steels Ct2Al23 and CoCr ate found in aluminum and cobalt-based alloys, respectively. The chromium-rich interstitial compounds, Ci2H, chromium nitrogen(2 l) [12053-27-9] Ct2N, and important role in the effect of trace impurities on the... 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

I. G. Wright, Oxidation of Iron-, Nickel-, and Cobalt-Base Alloys, MCIC Report 72-07, BatteUe-Columbus Laboratories, BatteUe Memorial Institute, 1972. 

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. 

Table 5. Compositions of Cobalt-Base Wear-Resistant Alloys, wt...

The abrasion resistance of cobalt-base alloys generally depends on the hardness of the carbide phases and/or the metal matrix. For the complex mechanisms of soHd-particle and slurry erosion, however, generalizations cannot be made, although for the soHd-particle erosion, ductihty may be a factor. For hquid-droplet or cavitation erosion the performance of a material is largely dependent on abiUty to absorb the shock (stress) waves without microscopic fracture occurring. In cobalt-base wear alloys, it has been found that carbide volume fraction, hence, bulk hardness, has Httie effect on resistance to Hquid-droplet and cavitation erosion (32). Much more important are the properties of the matrix. 

Alloy Compositions and Product Forms. The nominal compositions of various cobalt-base wear-resistant alloys are Hsted in Table 5. The six most popular cobalt-base wear alloys are Hsted first. SteUite alloys 1, 6, and 12, derivatives of the original cobalt—chromium—tungsten alloys, are characterized by their carbon and tungsten contents. SteUite aUoy 1 is the hardest, most abrasion resistant, and least ductile. 

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