The physical properties of some alternative alloys

Over the past 30 years the 'traditional' gold alloy systems have been modified by reducing the percentage of gold and other noble metals to the point where the 'non-precious metal' alloys have no noble metal content. These include the nickel-based alloys, cobalt-based alloys and certain experimental alloys, all suitable for porcelain application. This application demands castability, compatibility with investments, suitable finishing properties, appropriate thermal expansion, chemical bonding with porcelain, solderability and biocompatibility. Recent research into these functional requirements has (1) confirmed the role of Cr in corrosion resistance; (2) related high fusion temperatures to surface roughness and inaccurate fit; (3) demonstrated the importance of casting size and thickness; (4) related castability to the choice of investment for a particular alloy; (5) provided a method for controlling the deposition of oxide film upon the casting; and (6) shown that the re-use of base metal alloy has an adverse effect upon the mechanical properties of the casting. The expense of manipulating the base metal alloys to some extent offsets their cost-benefit advantage over traditional gold alloys. It is possible that Cr will not remain freely available, in which case its price too will soar.