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Search for new polycrystalline MC reinforced cobalt base superalloy candidate materials for application at 1200 ° C

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Document pages: 9 pages

Abstract: For applications above 1150 ° C, the best superalloy single crystal at present cannot be used under stress because its enhanced precipitation disappears at a temperature higher than its solution temperature. Strengthening cobalt based alloys with refractory and highly stable carbides may be an alternative solution. In this work, interest has focused on several types of MC carbides. The alloy was refined with atomic equivalent m elements (Ti, Ta, Nb, HF or Zr) and C elements. Script eutectic tic, TAC, NBC, HFC and ZrC carbides were successfully obtained between dendrites. Unfortunately, only one type of HFC showed high morphological stability at 1200 ℃ for about 50 hoursC. The concerned alloy, of the Co-25Cr-0.5C-7.4Hf type (in wt. ), was further characterized in flexural creep resistance and air-oxidation resistance at the same temperature. The creep behaviour was very good, notably by comparison with a more classical Co-25Cr-0.5C-7.5Ta alloy, proving that the interest of HfC is higher than the TaC one. In contrast the oxidation by air was faster and its behaviour not really chromia-forming. Significant improvements of this chemical resistance are expected before taking benefit from the mechanical superiority of this alloy.

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