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

Abstract

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.

Influence of Ti on the oxidation behaviour at 1250°C of chromia-forming alloys based on nickel and/or cobalt

“…Ti is often present in many superalloys, based on nickel [8,9] as well as on cobalt [10,11] and its role in the oxidation behaviour at high temperature of the concerned alloys can be important [12]. In presence of c arbon, titanium may lead to the formation of TiC carbides in nickel-based superalloys [13][14][15] as well as in cobalt-based superalloys [16]. In the field of high temperature metals and materials, TiC can be also met in composites [17] and coatings [18].…”

Diseño de aleación de alta entropía de alto desempeño mecánico en condiciones de bajas y altas temperaturas para aplicaciones energéticas y aeroespaciales.

“…Además, son fuertes refinadores de grano. Los precipitados primarios de Ti presentan tamaños superiores a 1 µm [78,79], los cuales se forman a altas temperaturas, presentando un gran crecimiento [80,81]. Los precipitados secundarios de Ti son nanométricos [80,81], favoreciendo un refuerzo efectivo desde la mecánica de precipitados al aumentar la capacidad de enmarañamiento y el esfuerzo cortante requerido para el flujo de dislocaciones en el plano de deslizamiento.…”