Effect of Mold Preheating on the Microstructure of the Investment Cast Astm F-75 Implant Alloy

The ASTM F-75 (Co-28%Cr-6%Mo) is widely used as a biocompatible alloy in medicinefor manufacturing implants. In this study, effect of mold preheating on the as-cast microstructure of thealloy was investigated using the solid investment casting process. Several mold preheating temperaturesof 550, 700, 850 and 1000 °C were selected at the same melt superheat. The samples were characterizedby optical microscopy, electron microscopy and macro-hardness test. The results showed that the size ofgrains and secondary carbides of the matrix was increased by increasing the mold preheatingtemperature. In addition, morphology of the M23C6 carbides was changed from the eutectic carbidesprecipitated in grain boundaries to the blocky shape precipitated in both carbide interface and dendriticmatrix. The appropriate microstructure with nearly fine grains with homogeneous distribution ofsecondary phases was obtained at mold preheating temperature of about 850 °C.