Effect of Microstructure on the Physical Properties of Cobalt-Base Alloys

¹ University of Michigan, School of Dentistry, Ann Arbor, Michigan

1. Microstructure as well as microporosities have a pronounced effect on the physical properties of Stellite 21.

2. Stellite 21 can be etched satisfactorily with a 2 per cent solution of chromic acid as an electrolyte and a low current produced by a 6-volt battery.

3. According to Badger and Sweeney's identification, three different types of carbide can be detected in this alloy by using a very light electrolytic etch in 2 per cent chromic acid followed by an alkaline permanganate etch of about 7 seconds.

4. Carbides that are spherical and discontinuous, like islands, demonstrate the highest elongation. The carbides in the form of grain boundaries which are continuous or dark eutectoid areas reduce the elongation of this alloy.

5. The temperature of the mold has little effect on the microstructure. High metal casting temperatures, however, results in spherical and discontinuous carbides, which, in turn, yield higher elongation values.