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High temperature oxidation of nickel-based alloys reinforced by hafnium carbides. Part 2: Metallography results

Patrice Berthod, Elodie Conrath

After a first part devoted to the oxidation kinetic at high temperature for HfC-containing nickel-based alloys this second part deals with the phenomena which can be post-mortem observed by metallography on the oxidizedNi-25Cr-0.25 to 0.50C-3.72-5.58Hf alloys. The samples generated in the first part were effectivelymetallographically prepared and analyzed by X-RayDiffraction and ElectronicMicroscopy observations. The three HfCcontaining alloys displayed very good behaviour in oxidation at 1200°C, similarly to the ternary alloys towhich theywere compared (chromia-forming behaviour, still high chromiumcontent in extreme surface after 46 hours of oxidation). TheirHfCinterdendritic carbide networkwas not greatly changed, neither in terms of nature and volume fraction, nor in term of morphology, this promising good sustainability of high mechanical properties at high temperature. These alloys are thus serious candidates for applications at very high temperature for which chromiummust replace aluminiumfor the chemical resistance at high temperature.