Dependence of titanium carbide stability at elevated temperatures on Co content in Co(Ni)-25Cr-1.6Ti-0.4C superalloys

Titanium carbides feature among the MC carbides which tend to crystallize with a script-like shape recognized to be favorable to mechanical strength at high temperature for equi-axed cast refractory alloys. Recent results demonstrated that script-like TiC can be successfully obtained in Co-based alloys while they are less stable than chromium carbides in nickel-based alloys. The present work aims to study whether the addition of cobalt to nickel-based alloys may stabilize TiC. This double investigation, by thermodynamic calculations and by the elaboration of a series of nickel-based alloys with an increasing part of cobalt, demonstrates that the progressive enrichment in cobalt tends favoring the presence of TiC instead chromium carbides. To obtain a majority of TiC, script-like shaped and in significant quantity, cobalt must be more present than nickel in the alloys. But this enrichment in cobalt deteriorates the good resistance against hot oxidation.