Amorphous Alloys Containing Cobalt for Orthopaedic Applications

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Abstract
Amorphous metal alloys have properties and structures unlike those of their crystalline counterparts. For example, a multiphase crystalline structure may exhibit poor corrosion resistance while the amorphous structure is corrosion resistant. The high hardnesses of some amorphous alloys may make them useful for wear resistant applications. Cobalt-based, electrodeposited alloys may be particularly compatible for producing desirable surfaces on orthopaedic Co-Cr-Mo alloys. Amorphous Co-20P alloy (A-Co-20P) has an as-deposited Knoop hardness number (HK) of ca 620. The surface of anodized A-Co-20P has been described elsewhere as predominately phosphorus oxide that may react with water to form an adsorbed hypophosphite layer. Others reported corrosion resistance without pitting. Hence, the potential of A-Co-20P for use as an implant coating to induce bony apposition was evaluated. This evaluation consisted of tests of corrosion resistance and solution chemistry. Another alloy, amorphous Co-Cr-C, was found to have an as-deposited HK of ca 690. Heat treatment produced Knoop hardness numbers (HKs) of ca 1350, between the HKs of zirconia and alumina. Wear and corrosion resistance are expected to be good, but adherence needs to be assessed.

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