抽拉速率对定向凝固Mar-M247LC高温合金微观结构及蠕变性能的影响

Effect of Withdrawal Rate on Microstructure and Creep Performance of Directionally Solidified Mar-M247LC Superalloy

摘要:

研究了抽拉速率对Mar-M247LC定向凝固镍基高温合金组织和持久性能的影响。结果表明：随着定向凝固试样抽拉速率的提高，一次枝晶间距逐渐减小，从479 μm降至322 μm；γ'相平均尺寸减小（在枝晶间区域从460 nm降至345 nm，在枝晶干区域从298 nm降至203 nm）。此外，碳化物形态由块状转变为汉字状。热处理后，试样中形成了规则的立方状γ'相，且热处理后试样中的γ'相含量较定向凝固试样有显著增加。在抽拉速率为40 μm/s的条件下凝固合金会形成细长状的γ'筏形组织、狭窄的基体通道及规则的位错网络，这些因素协同作用使蠕变断裂寿命延长至96.6 h。断口分析确认该合金的断裂模式为穿晶韧性断裂，裂纹萌生于分解的MC碳化物处。

Abstract:

The effect of withdrawal rate on microstructure and creep performance of directionally solidified (DS) Mar-M247LC superalloy was investigated. Results show that an increase in withdrawal rate of DS specimens leads to a reduction in primary dendrite arm spacing (from 479 μm to 322 μm), and the average size of γ' precipitate decreases from 460 nm to 345 nm in interdendritic region and from 298 nm to 203 nm in dendritic core. In addition, the carbide morphology changes from blocky to script-like. The heat treatment leads to the formation of distinct cuboidal γ' precipitates. And the volume fraction of γ' precipitates in heat-treated microstructure has a significant increase compared to that in DS microstructure. The DS superalloy under the withdrawal rate of 40 μm/s exhibits elongated raft-like γ' structure with narrowed matrix channels and regular dislocation networks, synergistically prolonging creep rupture life to 96.6 h. Fractographic analysis confirms that the superalloy exhibits a transgranular ductile fracture mode, with cracks initiating at decomposed MC carbides.