Methods and mechanisms for uniformly refining deformed mixed and coarse grains inside a solution-treated Ni-based superalloy by two-stage heat treatment
Methods and mechanisms for uniformly refining deformed mixed and coarse grains inside a solution-treated Ni-based superalloy by two-stage heat treatment
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DOI：
10.1016/j.jmst.2020.11.030
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发表时间：
2021-06
影响因子：
10.9
通讯作者：
Guan-Qiang Wang;Ming-Song Chen;Hong-bin Li;Y. C. Lin;Weixuan Zeng;Yanyong Ma
中科院分区：
文献类型：
--
作者：
Guan-Qiang Wang;Ming-Song Chen;Hong-bin Li;Y. C. Lin;Weixuan Zeng;Yanyong Ma
研究了固溶镍基高温合金在两段退火过程中变形混合晶粒和粗晶粒均匀细化的机理和方法。两阶段热处理实验包括时效退火处理（AT）和随后的再结晶退火处理（RT）。热处理的目的是在热处理过程中析出一些δ相并消耗一部分储存能量来抑制晶粒长大，而热处理的目的是通过再结晶来细化混合晶粒和粗晶粒。可以发现，AT时间过低或RT温度过高时，再结晶晶粒会迅速长大，而AT时间过长或RT温度过低时，变形的粗晶粒无法消除。另外，当AT时间为3 h， RT温度为980℃时，退火试样中可以观察到由一些异常粗再结晶晶粒（ACRGs）和大量细晶粒组成的混合显微组织。这种现象是由于AT时间过短时变形能不均匀导致δ相分布不均匀所致。在δ相较多的区域，再结晶成核速率加快，晶粒长大受到限制，形成细小晶粒。而在δ相较少的区域，晶界周围的再结晶晶粒容易长大，晶粒内部很难形成新的再结晶核，从而导致ACRGs的发生。因此，为了获得均匀精细的退火组织，选择合适的AT时间，如12h，是析出分布均匀的δ相的前提。此外，还需要较高的RT温度，以促进δ相周围的再结晶成核。混合晶体均匀细化的最佳退火参数范围为：900℃×12 h + 990℃×（40−60 min）和900℃×12 h + 1000℃×（10−15 min）。
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated. The two-stage heat treatment experiments include an aging annealing treatment (AT) and a subsequent recrystallization annealing treatment (RT). The object of AT is to precipitate someδphases and consume part of storage energy to inhibit the grain growth during RT, while the RT is to refine mixed and coarse grains by recrystallization. It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high, while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low. In addition, the mixed microstructure composed of some abnormal coarse recrystallization grains (ACRGs) and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT temperature is 980 ℃. The phenomenon attributes to the uneven distribution ofδphase resulted from the heterogeneous deformation energy when the AT time is too short. In the regions with a large number ofδphases, the recrystallization nucleation rate is promoted and the growth of grains is limited, which results in fine grains. However, in the regions with fewδphases, the recrystallization grains around grain boundaries can easily grow up, and the new recrystallization nucleus is difficult to form inside grain, which leads to ACRGs. Thus, in order to obtain uniform and fine annealed microstructure, it is a prerequisite to precipitate even-distributedδphase by choosing a suitable AT time, such as 12 h. Moreover, a relative high RT temperature is also needed to promote the recrystallization nucleation aroundδphase. The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as: 900 ℃×12 h + 990 ℃×(40−60 min) and 900 ℃×12 h + 1000 ℃×(10−15 min).