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This is Muntz metal, a brass with 40% zinc, shown at 200X at
left. It has been air cooled from the all-beta
region at 825C. Note the pronounced Widmanstaetten alpha. How
would a quenched specimen differ from this ? What about a slowly cooled specimen ? The alpha precipitates inside the beta grains and on the beta grain boundaries. The alpha appears as long, fat needles in a beta matrix. There would be much less alpha (if any) if this specimen had been quenched, and more and "rounder" precipitates if slowly cooled (i.e., closer to the equilibrium structure). Pause and think a while before looking at the next page. |