High temperature alloys were mostly used in the gas turbine industry for a long while. Along with the ability to be retain its strength in high temperature conditions, gas turbines on aircrafts required materials that could also resist oxidation and thermal fatigue. For aircraft that used a lower grade of fuel, the main concern was sulfidation-resistance as they operated at lower temperatures. Cobalt-based alloys were best used for these turbines as they provided the necessary sulfidation-resistance.
The use of high-temperature alloys today vastly differentiates from how they were used decades ago. We have learned to burn waste and fossil fuels more efficiently and developed new techniques for processing chemicals. High-temperature alloys may not be used as they were in the past, but they are still highly sought after for their unique applications. Cobalt-base high temperature alloys have the ability to retain strength in extremely high temperatures where gamma-double-prime- and gamma-prime- variations in both nickel and nickel-iron alloys dissipate.
Some of the more diversely used high-temperature alloys are nickel and nickel-iron. Their wide range of uses does little to compete with cobalts demagnetization-resistance, wear-resistance, and corrosion resistance.
This high temperature alloy is chemically composed of 20-23% percent chromium, 7-15% tungsten, 10-22% nickel, 3% iron, and 0.1-0.6% carbon. Cobalt is usually used to make up the rest of the mixture.
Cobalt is also commonly used in nickel base alloys to improve heat resistance as the melting point rises from 1,728 K to 1,768 K when cobalt is used as the base element. Nickel’s melting point is still relatively high, but it loses strength as the temperature in increased. Cobalt can also be used in various materials including:
Artificial y-ray sources
Cemented tool steels and carbides
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