Cobalt-chrome

[2] Under the name Stellite, Co-Cr alloy has been used in various fields where high wear-resistance was needed including aerospace industry,[3] cutlery, bearings, blades, etc.

In the 20th century, the alloy was first used in medical tool manufacturing,[4] and in 1960, the first Co-Cr prosthetic heart valve was implanted, which happened to last over 30 years showing its high wear-resistance.

[5] 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.

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.

[4] Co-Cr alloys show high resistance to corrosion due to the spontaneous formation of a protective passive film composed of mostly Cr2O3, and minor amounts of cobalt and other metal oxides on the surface.

[8] Good mechanical properties that are similar to stainless steel are a result of a multiphase structure and precipitation of carbides, which increase the hardness of Co-Cr alloys tremendously.

[3] Depending on the percent composition of cobalt or chromium and the temperature, Co-Cr alloys show different structures.

[4] Co-Cr alloys tend to be corrosion resistant, which reduces complication with the surrounding tissues when implanted, and chemically inert that they minimize the possibility of irritation, allergic reaction, and immune response.

[14] The alloy composition used in orthopedic implants is described in industry standard ASTM-F75: mainly cobalt, with 27 to 30% chromium, 5 to 7% molybdenum, and upper limits on other important elements such as less than 1% each of manganese and silicon, less than 0.75% iron, less than 0.5% nickel, and very small amounts of carbon, nitrogen, tungsten, phosphorus, sulfur, boron, etc.

Metals released from Co-Cr alloy tools and prosthetics may cause allergic reactions and skin eczema.