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Microstructure and oxidation behavior at 1100°C of nickel-base alloys containing hafnium carbides

Patrice Berthod, Elodie Conrath

Three nickel-base alloys containing 25wt.%Cr, 0.25 to 0.50wt.%C andHf contents high enough to obtain significant hafnium carbides for achieving high strength at high temperature were elaborated by foundry then exposed at 1100°C for 46 hours. Afterwards they were observed in cross section and submitted to indentation tests. Interdendritic HfC carbides were successfully obtained, alone for given Hf/C atomic percent ratio or with additional Cr carbides. The HfC volume fractions slightly decreased during the 1100°C stage while, inversely, chromium carbides grew a little.The room temperature hardness was lowered of 25- 40Hv consecutively to the HfC fragmentation occurred during the 1100°C stage. The cross-sectional surface characterization showed that the three alloys well behaved in oxidation at 1100°C, with an external chromia scale and Cr content remained high in subsurface.