ABSTRACT In this work, nickel is added in substitution to cobalt in the composition of a cast cobalt-based chromium-rich superalloy designed to obtain a double-phased {fcc matrix + TaC} microstructure. Two nickel amounts were tested, 13 and 26 wt-%Ni, for 25 wt-%Cr, 0.4 wt-%C and 6 wt-%Ta, the rest being cobalt. The obtained as-cast microstructures are not different from the starting alloy's one, contrarily to the hardness which became lower. The oxidation tests at 1200°C for 170 h demonstrated a significant improvement of the alloy's behaviour, especially for an addition of 26 wt-%Ni. This seems to be attributed to an easier Cr diffusion towards the oxidation front as suggested by the observed Cr contents in extreme surface as well as by the lower Cr concentration gradients. In addition, the TaC seemed to be morphologically more stable in the presence of nickel in the alloys than in the absence of Ni.

中文翻译：

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添加镍改善 TaC 强化 Co(Cr) 基铸造高温合金的高温氧化

摘要在这项工作中，镍被添加到钴基铸造富铬高温合金的成分中以替代钴，旨在获得双相 {fcc 基体 + TaC} 微观结构。测试了两种镍量，13 和 26 重量％Ni，用于 25 重量％Cr、0.4 重量％C 和 6 重量％Ta，其余为钴。所获得的铸态显微组织与起始合金的显微组织没有区别，相反，硬度变得更低。在 1200°C 下进行 170 小时的氧化测试表明合金的行为得到了显着改善，尤其是添加了 26 wt-% Ni。这似乎归因于更容易的 Cr 向氧化前沿扩散，正如在极端表面观察到的 Cr 含量以及较低的 Cr 浓度梯度所表明的那样。此外，