Abstract
The effects of cooling rate during solidification and of subsequent heat treatment on the microstructure and hardness of two cobalt base Co–Mo–Cr–Si alloys have been investigated. It had been thought that the solid solution constituent of these alloys in the cast condition had the fcc crystal structure, but both the fcc and hcp forms were found with the hcp phase being dominant. The amount of hcp fell at the fastest cooling rate studied, but the microstructure was generally relatively insensitive to cooling rate. The as-cast alloys could be softened or hardened by subsequent heat treatment and these hardness changes are discussed in terms of the fcc ⇌ hcp allotropic transformation and a precipitation reaction.
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