Chemical cobalt-based alloys

The nickel base alloys are produced from a group of alloys which have chemical compositions generally over 50 % nickel and less than 10 % iron. They are mainly strengthened by intermetallic precipitation in an austenitic matrix. The cobalt base alloys have a high Co content (40 to 70 %X high Cr (over 20 %), high W (7 to 15 %) and they are strengthened by a combination of carbides and solid solution hardeners. 

A wide variety of metals is produced for industries such as automotive, aerospace, marine, energy, chemical processing, etc. Materials include aluminum, titanium, stainless steel, nickel- and cobalt-base alloys, tool steels, and materials for electronic, magnetic, and expansion applications. Regardless of the metal, the stime selection process can be used. 

The materials currently used in the production of medical devices include stainless steels, cobalt-base alloys, titanium-base alloys, platinum-base alloys, and nickel-titanium alloys. Steels were the first modern metallic alloys to be used in orthopedics and initial problems with corrosion were overcome by modifying the composition of the steel with the addition of carbon, chromium, and molybdenum. Carbon was added at low concentrations (ca. 0.03-0.08%) to initiate carbide formation, while the addition of chromium (17-19%) facilitated the formation of a stable surface oxide layer and the presence of molybdenum (2.0-3.0%) was found to control corrosion. The compositions of stainless steels used can vary widely. Table V shows the limits for the chemical compositions of three different alloys containing eleven different elements together with the mechanical properties for the samples after annealing and cold working. 

Table 2-13. Approximate chemical composition of wrought cobalt-based alloys.

TABLE E.13 Chemical Compositions of Nickel-, Nickel-Iron-, and Cobalt-Base Alloys... 

Besides nickel, cobalt, and copper-based alloys, there are other industrial non-ferrous corrosion-resistant metals such as the reactive metals zirconium, titanium, niobium, and tantalum. Table 2-18 shows the chemical composition and UNS designations of the reactive metals alloys. 

Cobalt is present in almost all nickel ores. Previously there was no use for cobalt and as its value was less than that of nickel, it was not separated. Therefore, old nickel alloys contain much more cobalt than those of the present day. Two chemical methods are based on the oxidation of cobalt to three-valent ions. Cobalt is precipitated as cobalt(III) hydroxide by treating the solution with chlorine to oxidize the cobalt(II) to cobalt(III) and adding nickel carbonate to control the pH to 4 (27)... 

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