Cobalt-chrome

Cobalt-chrome or cobalt-chromium (CoCr) is a metal alloy of cobalt and chromium. Cobalt-chrome has a very high specific strength and is commonly used in gas turbines, dental implants, and orthopedic implants.

Co-Cr alloy was first discovered by Elwood Haynes in the early 1900s by fusing cobalt and chromium. The alloy was first discovered with many other elements such as tungsten and molybdenum in it. Haynes reported his alloy was capable of resisting oxidation and corrosive fumes and exhibited no visible sign of tarnish even when subjecting the alloy to boiling nitric acid. Under the name Stellite™, Co-Cr alloy has been used in various fields where high wear-resistance was needed including aerospace industry, cutlery, bearings, blades, etc. Co-Cr alloy started receiving more attention as its biomedical application was found. In the 20th century, the alloy was first used in medical tool manufacturing, and in 1960, the first Co-Cr prosthetic heart valve was implanted, which happened to last over 30 years showing its high wear-resistance. Recently, due to excellent resistant properties, biocompatibility, high melting points, and incredible strength at high temperatures, Co-Cr alloy is used for the manufacture of many artificial joints including hips and knees, dental partial bridge work, gas turbines, and many others.

The common Co-Cr alloy production requires the extraction of cobalt and chromium from cobalt oxide and chromium oxide ores. Both of the ores need to go through reduction process to obtain pure metals. Chromium usually goes through aluminothermic reduction technique, and pure cobalt can be achieved through many different ways depending on the characteristics of the specific ore. Pure metals are then fused together under vacuum either by electric arc or by induction melting. Due to the chemical reactivity of metals at high temperature, the process requires vacuum conditions or inert atmosphere to prevent oxygen uptake by the metal. ASTM F75, a Co-Cr-Mo alloy, is produced in an inert argon atmosphere by ejecting molten metals through a small nozzle that is immediately cooled produce fine powder of the alloy.

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