形变及热处理对GH3625合金晶界特征分布的影响

Effect of Thermo-Mechanical Processing on Grain Boundary Character Distribution of GH3625 Superalloy

摘要:

在不改变GH3625合金化学成分的前提下,通过晶界工程(GBE)优化和调控合金组织,从而改善合金的高温组织稳定性以及使用可靠性。采用电子背散射(EBSD)和取向成像显微技术(OIM)研究了形变热处理对GH3625合金晶界特征分布(GBCD)的影响。结果表明,GH3625合金晶界特征分布的优化主要是通过再结晶过程中形成的Σ3_n晶界来实现的,同时主要受冷变形量和退火条件的影响；GH3625合金中低ΣCSL晶界比例随着冷变形量的增加而减小,随着退火温度的升高而增加,当合金在ε=35 %,退火温度为1120 ℃保温15 min时,低ΣCSL晶界比例可提高到63.16 %以上(Palumbo-Aust标准)；同时形成大尺寸的“互有Σ3_n的取向关系晶粒的团簇”此外,GH3625合金中出现了大尺寸的晶粒团簇,在晶粒团簇内的晶粒之间具有Σ3_n的取向关系；晶粒团簇尺寸和内含Σ3_n晶界的数量随着冷变形量的增加而减小,随着退火温度的升高而增加。

Abstract:

In this work, Grain boundary engineering (GBE) is used to optimize and control the microstructure of this alloy approach to advancing without changing chemical composition of GH3625 alloy, thereby, improving the high temperature microstructure stability and service performance reliability of the alloy. The effect of thermal-mechanical processing on the grain boundary character distribution (GBCD) of GH3625 superalloy was investigated by means of the electron backscattered diffraction (EBSD) technique and orientation image microcopy (OIM). The results show that the optimization of the grain boundary character distribution (GBCD) of GH3625 superalloy is mainly achieved byΣ3_n grain boundaries formed during the recrystallization process, and is mainly affected by the cold deformation and annealing process. The length fraction of low ΣCSL grain boundaries in GH3625 superalloy decreases with the increase of cold deformation and increases with the annealing temperature. Meanwhile, the length fraction of low ΣCSL (coincident site lattice, Σ ≤29 by Palunbo-Aust criterion) grain boundaries increase to more than 63.16 % by thermal-mechanical processing after 35 % cold deformed and subsequent annealing at 1120 ℃ for 15 min. In addition, large sized grain-clusters appear in GH3625 superalloy, and boundaries have Σ3_nmisorientations inside the grains-cluster. The size of the grain-clusters and the amount of Σ3_n grain bounaries inside the grains-cluster decreases with the increase of cold deformation and increases with the annealing temperature.