Abstrakt

Hafnium carbides in cast chromium-rich refractory alloys. Part 1: Case of nickel-based alloys

Patrice Berthod

Hafnium, generally used for the improvement of the behaviour of the superalloys in high temperature oxidation, is also a strong carbide-former element. It forms MC carbides which can be extremely stable at very high temperature in some refractory alloys. In thiswork itwas attempted to develop an interdendritic carbides network partly or wholly made of eutectic HfC carbides, in chromium-rich nickel-based quaternary alloys. Three Ni-25CrxC- yHf (contents inwt.%)with x belonging to {0.25; 0.50} and y{3.7; 5.6} were elaborated by induction foundry under inert atmosphere, then characterized in the microstructure field and in hardness. The obtained microstructures effectively show dendritic matrixes and interdendritic HfC carbides forming a eutectic with thematrix, this type of carbides being either the single one or being mixed with eutectic chromium carbides. Thanks to the presence of these carbideswith rather great volume fractions the hardness of the HfC-containing alloys is higher than the ones of ternary nickel alloys with the same chromium and carbon contents, also elaborated in this work for allowing such comparisons.