Cobalt alloy (Trade Name Hiperco or Vanadium Permundur) laminations are necessary in certain applications, but due to their very high cost must be considered a last resort after examining the other alternatives. Their primary use is in applications requiring the highest possible flux density without saturation. Typical Saturation is as high as 22-23 kG. Most frequently, they find use in airborne and other weight sensitive applications where less metal can be used to carry the required flux. The grade commonly used has 48-50% Cobalt, with the balance iron, and 2% vanadium. It occasionally finds use where its high tensile strength is advantageous, but stress is seldom a primary design criteria for laminations.
Like the nickel alloys, Cobalt alloy requires a very precise annealing
after stamping, and must be insulated with an oxide coating. It does not
require the high temperatures of nickel, but a dry hydrogen atmosphere is
necessary. The parts must be brought to within a narrow temperature and, and if a critical temperature is exceeded, the magnetic properties will be destroyed and the parts must be scrapped. This critical temperature varies with material supplier, but is around 1625 F. The material supplier must be consulted before specifying an annealing cycle. The cooling rate must be closely controlled to get the best results. An oxide coating is usually added as a separate process.