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Techniques of optical, scanning, carbon extraction replica and thin foil transmission electron microscopy were used to study the structure, shape and size distribution of nine internal oxides, produced from copper alloys containing 1 to 5 weight % of the alloying element. These internal oxides, dispersed in the copper 'carrier metal' matrix, were each used to inoculate molten, pure copper metal to encourage grain refinement of the solidified metal structure. One oxide in particular, Cr203, was found to produce effective grain refinement. Critical experiments were performed, which involved undercooling measurements, dihedral oxide-copper contact angle determination and observations of crystallographic orientation relationships, developed between oxides and a copper matrix. These experiments provided some evidence for the proposal that the mechanism of grain refinement was 'classic' heterogeneous nucleation. The nucleation is discussed in terms of wetting of the nuclei particles by molten copper, with 'good' wetting achieved with low contact angle (< 900) between the nucleant and solidifying metal. Symmetry of structure and low lattice disregistry between the nucleant oxide substrate and the solidifying metal appear to be important prerequisites for heterogeneous nuclei. The grain refining ability of a nucleant addition was found to be critically dependent upon the casting conditions and also upon the possibility of developing constitutional supercooling in the solidifying metal. There is evidence that the distribution of internal oxides in a molten metal is unstable so that particle segregation occurs shortly after transference, and this may be responsible for reduced grain refinement.

Of all the stories and articles written about Captain J.A. Sutter in recent years, not one of them has adequately covered the history of his famous Fort. To the layman the fort itself may seem unimportant, but when we stop to consider that it was an outpost of civilization penetrating the wilderness of Central California, offering shelter to those who pioneered before us; we must confess that its existence was necessary to protect and usher into full City-hood, the infant Sacramento, then known as New Helvetia.

54p.

80p.