Effect of Cooling Rate on Microstructure, Microporosity, and Segregation Behavior of Co-Al-W Alloys Prepared by Vacuum Induction Melting

The work focuses on the investigation of technological properties of new γ′-type strengthened Co-based superalloys, including cooling rate effects on the as-cast microstructure and microsegregation of polycrystalline Co-Al-W-based superalloys. To vary the cooling rate, alloys prepared via vacuum induction melting (VIM) were cast to different types of casting molds. The crystallization time of the alloys was determined via direct temperature measurement of the solidifying metal. Microstructural parameters such as porosity and secondary dendrite arm spacing (SDAS) were evaluated using image analysis. The influence of cooling rate on the microsegregation of the alloying elements was also determined. The average volume fraction of pore shrinkage was the lowest for the fast-solidified alloy. The cooling rate did not affect gas porosity, whereas decreasing the cooling rate increased SDAS, similarly to that of commercial Ni-based superalloys. A reduced solidification speed did not cause the formation of unexpected phases but resulted in increased macro- and microsegregation.