变形高温合金长期服役中一次碳化物退化对强化相和晶界的失稳性扰动

With the rapid development of superalloy in energy area, the service life is expected to be as long as thousands of hours. Hence, it is of vital importance to get a comprehensive understanding of microstructure stability and disturbance factors during long term service of superalloy. It is widely accepted that primary carbide in wrought superalloy is a stable phase during long term aging and much attention is paid on dispersion strengthening phases and grain boundaries in previous study of long term aging stability of wrought superalloy. However, the preliminary study of the applicant shows that primary carbide in wrought superalloy is not stable during long term aging and can release large amounts of elements into matrix. The decomposition of primary carbide in wrought superalloy serves as a slow-releasing “spring” of elements during aging and accelerates the deterioration of strengthening phases and grain boundaries through element redistribution. As a result, the present study is aimed at exploring the stability of primary carbide during long term aging in wrought superalloy. And on this basis the influence of primary carbide degeneration on the instability of strengthening phase and grain boundary during long term aging is studied. Furthermore, an element redistribution relationship between phases and a dynamic model for primary carbide decomposition are established. The results hope to supplement the understanding of microstructure instability for wrought superalloy during long term aging.

高温合金超长寿命随着能源领域高歌猛进必将引起极大关注，动辄数万小时安全服役必对组织稳定性提出极高要求，为此对超长服役过程中组织稳定性扰动的全掌控就更为突出。而变形高温合金一次碳化物在服役温度范围通常被认为具有较高稳定性，故以往组织稳定性皆侧重于弥散强化相和晶界的研究。但申请人在对变形高温合金长期服役过程中一次碳化物开展的初步研究中观察到，其并非稳定甚至在失稳过程中会释放大量合金强化元素，类似服役过程中合金元素缓慢释放“源泉”，经再分配势必会对强化相和晶界稳定性导致再影响，对合金组织失稳带来加速扰动作用。为此，提出本次项目申请思路，首先通过典型变形高温合金长期时效试验明确一次碳化物的稳定性，在此基础上得到一次碳化物分解对强化物和晶界失稳的扰动，并构建时效过程中合金元素的再分配规律，最后建立一次碳化物分解的动态模型。从而完善、补充变形高温合金长期服役组织失稳的认知体系。

变形高温合金在航空航天、石油、电站等领域有广泛应用，合金长期服役稳定性至关重要。本研究首先对多种典型镍基变形高温合金在近服役温度范围内开展了长达一万小时的长期时效实验，对时效过程中一次碳化物、相等的演变规律进行了分析，并通过萃取相分析手段进行了析出相含量和元素组成的精确定量表征。多种表征手段相结合明确了变形高温合金的一次碳化物在近服役条件长期时效过程中可以发生分解反应。. 在此基础上，对分解过程中的一次碳化物形貌特征、周围元素分布特点进行了细致分析，细化了变形高温合金一次碳化物分解的过程方程。并且将一次碳化物的演化行为与合金中其他析出相的演化规律进行比对分析，发现在一次碳化物分解过程中释放的合金元素会引起基体中元素的“扰动”，并通过元素再分配的方式影响其他强化相和晶界析出相的演变规律，获得了变形高温合金长期服役过程中的元素再分配规律。从而提出了一种将服役过程中析出相演变规律通过元素的再分配行为进行整体分析的研究思想，探究了一次碳化物分解对强化相和晶界稳定性的影响。采用溶度积的概念结合热力学和动力学计算，明确了一次碳化物在近服役条件长期时效过程中分解的原因。采用经典公式结合理论计算，构建了一次碳化物分解的动态模型，与实验结果有较好的吻合度。. 通过大量实验和理论计算，明确了变形高温合金中一次碳化物可分解这一现象，并对分解的机理和影响进行了系统性探究，为变形高温合金长期服役稳定性的考评提出了新的关注点和理论参考。