Microstructural evolution and grain refinement mechanisms of a Ni-based superalloy during a two-stage annealing treatment
Microstructural evolution and grain refinement mechanisms of a Ni-based superalloy during a two-stage annealing treatment
复制标题
镍基高温合金两阶段退火过程中的显微组织演变和晶粒细化机制
DOI：
10.1016/j.matchar.2019.03.037
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发表时间：
2019-05-01
影响因子：
4.7
通讯作者：
Ma, Yan-Yong
中科院分区：
文献类型：
--
作者：
Chen, Ming-Song;Zou, Zong-Huai;Ma, Yan-Yong
在作者以前的工作中[Mater.Charact，141(2018)212-222]发现，通过一次退火处理，可以用相对均匀的再结晶晶粒取代非均匀变形的显微组织。但仍有一些较大的再结晶颗粒。在本研究中，为了更好地细化晶粒和改善均匀性，设计了对变形样品进行两段式退火处理的试验。结果表明，与单级退火相比，两级退火能更好地细化组织，改善组织的均匀性。因此，获得了更均匀的颗粒分布。根据新的实验结果，讨论了变形粗晶的细化和均匀化机理。研究发现，当温度为900℃时，在第一阶段的再结晶晶界附近容易析出三角洲相，析出的三角洲相能有效地抑制再结晶晶粒的长大。但随着退火时间的延长，由于Nb元素含量的减少，β相的析出速率逐渐降低。因此，钉扎力越来越小，后续形成的再结晶晶粒长大到相对较大的尺寸。因此，第一阶段退火热处理的保温时间对最终的晶粒度和三角洲相含量有很大的影响。在第二阶段退火热处理过程中，由于温度升高导致形核率的提高，以及三角洲相的钉扎作用，使得组织均匀细小。可行的工艺参数为：第一步退火温度900℃，保温时间9~12h，第二步退火温度980℃，时间60min。
In authors' previous work [Mater. Charact., 141(2018)212-222], it was found that the heterogeneous deformed microstructures can be replaced by the relatively homogeneous recrystallized grains through a single annealing treatment. However, there are still some relatively large recrystallized grains. In this study, two-stage annealing treatment tests for the deformed samples are designed to better refine the grains and improve the homogeneity. Results showed that the two-stage annealing treatment can better refine grains and improve the microstructural homogeneity compared with single annealing treatment. Thus, the more uniform distribution of grains is obtained. Based on the new experimental findings, the mechanisms for refining and homogenizing the deformed coarse grains are discussed. It is found that the delta phase can easily precipitate around the boundaries of re crystallization grains in the first annealing stage when the temperature is 900 degrees C. The precipitated delta phase can effectively inhibit the grain growth. However, with increasing annealing time, the precipitation rate of delta phase gradually decreases due to the decreased Nb element content. So, the pinning force becomes smaller and smaller, and the follow-up formed recrystallization grains grow to a relatively large size. Therefore, the holding time of first stage annealing treatment has a great influence on the final grain size and the content of delta phase. During the second stage annealing treatment, the increasing nucleation rate induced by the higher temperature and the pinning effects of delta phase make the uniform and fine grains. The feasible parameters are as follows: the first stage annealing treatment is 900 degrees C for 9-12 h and the second stage annealing treatment is 980 degrees C for 60 min.