Mo和W对DZ409镍基高温合金在900 ℃/1000 h下组织稳定性的影响

Effects of Mo and W on Microstructure Stability of DZ409 Nickel-Based Superalloy at 900 °C/1000 h

摘要:

重型燃气轮机用镍基高温合金通常具有较高的Cr含量，但高Cr含量给合金的成分设计优化带来了困难。特别是，为了避免有害拓扑密排（TCP）相的析出，限制了固溶强化元素W、Mo的含量。本工作采用复杂多组元扩散多元节技术，研究了W、Mo含量变化对燃机用镍基定向高温合金DZ409在900 ℃、1000 h时效条件下γ/γ′两相状态和TCP相析出的影响作用。实验结果表明：当Mo含量不变时，W含量由3.8wt%继续增加至4.3wt%时，γ′相体积分数略有减少，γ′相尺寸减小且形貌保持球形。当W含量超过4.3wt%时，合金中开始析出σ相和P相。当Mo含量由1.4wt%增加至1.6wt%，同时W含量从4.0wt%降至3.3wt%时，γ′相体积分数略有增加，γ′相尺寸减小且形貌保持方形。Mo 含量超过1.6wt%后，合金中析出σ相和P相。根据APT尖端重构图和各主要元素的离子分布图可知，W含量增大会促进TCP相析出，添加 Mo同时减少W也会促进合金析出TCP相，主要因为W、Cr等元素在γ基体中的富集，使γ相中难熔元素总量超过γ基体固溶极限。

Abstract:

Nickel-based superalloys for heavy-duty gas turbines usually have a high Cr content, but the high Cr content makes it difficult to optimize the composition design of the alloy. In particular, in order to avoid the precipitation of harmful topologically close-packed (TCP) phases, the content of solution-strengthening elements W and Mo is limited. In this work, the effects of W and Mo content changes on the γ/γ′ two-phase state and TCP phase precipitation of nickel-based directional superalloy DZ409 for gas turbines aged at 900 °C for 1000 h were studied by multi-component diffusion multi-junction technique. The results show that when the Mo content remains unchanged, the volume fraction of the γ′ phase decreases slightly as the W content increases from 3.8wt% to 4.3wt%, the size of the γ′ phase decreases, and its morphology remains spherical. When the W content exceeds 4.3wt%, σ and P phases begin to precipitate in the alloy. When the Mo content increases from 1.4wt% to 1.6wt%, and the W content decreases from 4.0wt% to 3.3wt%, the volume fraction of the γ′ phase increases slightly, the size of the γ′ phase decreases, and the morphology remains square. After the Mo content exceeds 1.6wt%, the σ phase and P phase are precipitated in the alloy. According to the APT tip reconstruction diagram and the ion distribution map of each major element, it can be seen that the increase in W content will promote the precipitation of TCP phase, and the addition of Mo while reducing W content will also promote the precipitation of TCP phase of the alloy, mainly because the enrichment of W, Cr, and other elements in the γ matrix makes the total amount of refractory elements in the γ phase exceed the solid solution limit of γ matrix.