COOLING BEHAVIOR AND MICROSTRUCTURE OF RAPIDLY SOLIDIFIED AG-CU ALLOYS

A systematic experimental approach has been used to study rapid solidi fication of Ag-Cu alloys with 23, 28.1 (eutectic), and 33 wt-%Cu using a levitation casting technique. The cooling curves were recorded duri ng each experimental run and the microstructure was examined. Differen t cooling rates were obtained ranging from 3.2 x 10(4) to 10 x 10(4) K s(-1), with nucleation undercoolings of 35-132 K, while growth underc ooling was in the range 12-52 K. Under these conditions, the microstru cture did not exhibit any lamellar structure. Instead, several other s tructures were obtained mainly, microsegregation free, banding, column ar; and equiaxed dendritic structures. A correlation was made between each type of structure, the cooling rate, and the nucleation undercool ing. The results are discussed and compared with previous work.