热处理对铸造镍基高温合金弯曲晶界演化和拉伸性能的影响

Effect of Heat Treatment on the Evolution of Serrated Grain Boundaries and Tensile Properties of a Casting Ni-based Superalloy

摘要:

针对燃机涡轮叶片用铸造镍基高温合金在服役温度区间的中温脆性问题,通过调控合金固溶后冷却速率及水淬终止温度,探究了 γ′ 相析出与晶界几何形态的协同演化规律对650 ℃拉伸性能的影响机理。研究发现,降低冷却速率与水淬终止温度促进了晶内 γ′ 相粗化,并驱动晶界由平直向弯曲形态演变。固溶后5 ℃/min的冷却诱导 γ′ 相强钉扎形成SGB-1型弯曲晶界,1 ℃/min的冷却诱导粗大的 γ′ 相与晶界协同迁移形成SGB-2型弯曲晶界。随冷却速率和水淬终止温度降低,合金650 ℃的屈服强度下降,但延伸率显著提升,其中具有SGB-2特征样品塑性达到8.5%。空冷样品的脆性源于强晶内-弱晶界的强度失配,而缓冷样品降低部分晶内强度换取弯曲晶界强化,构建强晶界-弱晶内匹配,从而有效缓解650 ℃拉伸脆性。

Abstract:

This work investigated the mitigation of intermediate temperature embrittlement in casting Ni-based superalloys for gas turbine blades. By tailoring the post-solution cooling rate and water quenching termination temperature, we analyzed the impact of the synergistic evolution between γ′ phase precipitation and grain boundary (GB) geometry on 650 °C tensile performance. It was found that lower cooling rates and quenching termination temperatures promote intragranular γ′ phase coarsening and a transition from planar to serrated GB morphologies. A cooling rate of 5 °C/min led to SGB-1 type serrated GBs via strong γ′ phase pinning, while 1 °C/min resulted in SGB-2 type serrated GBs through the synergistic migration of coarse γ′ phases and GBs. Although yield strength at 650 °C decreased with reduced cooling rates, ductility was significantly enhanced, with the SGB-2 sample achieving an elongation of 8.5%. The brittleness observed in air-cooled samples was attributed to a mismatch between strong grain interiors and weak grain boundaries. In contrast, slow-cooled samples effectively alleviated this brittleness by sacrificing some intragranular strength in favor of GB strengthening through serration, creating a beneficial "strong GB–weak grain interior" balance.