Inconel 718合金δ相的溶解动力学

Dissolution kinetics of δ phase in Inconel 718 alloy

采用X射线衍射技术测定了Inconel 718合金中δ相在980、1 000和1 020℃时的溶解动力学,并采用扫描电镜进行了组织观察。结果表明:Inconel 718合金在980、1 000和1 020℃保温过程中,δ相含量逐渐降低,经1 020℃保温2 h后,δ相可完全溶入基体;当温度为980和1 000℃时,δ相的平衡含量分别约为3%及0.6%。δ相的溶解过程可分为两个阶段,溶解初期主要表现为长针状δ相长度方向的断裂,且很快溶解断裂为短棒状及颗粒状,同时在厚度方向上尺寸逐渐减小;随着溶解过程的进行,后续的溶解过程主要为短棒状及颗粒状δ相尺寸的减小。δ相溶解动力学过程的控制环节并非Nb或Ni原子的长程扩散过程,而为δ相分解的界面反应过程。

The dissolution kinetics and microstructures evolution of δ phase in Inconel 718 alloy during holding at 980, 1 000 and 1 020 ℃ were analyzed using X-ray diffraction and scanning electron microscopy. The results indicate that the dynamic equilibrium state reaches after holding at 980 ℃ for more than 30 min and at 1 000 ℃ for more than 2 h, the equilibrium contents are 3.0% and 0.6%, respectively. Nearly, the δ phase dissolves into the austenitic matrix holding at 1 020 ℃ for more than 1 h. The dissolution process of needle-like δ phase can be divided into two stages, the initial stage is mainly characterized as the fracture from long needle shape to short bars or particles. Then, the size of δ phase with short bars or particles decrease at the following stage. The dissolution models of δ phase were established and the controlling step was revealed. The whole dissolution process is governed by the interface reaction mechanism, but not by the long-distance diffusion of Nb or Ni atoms in the austenite matrix.