Microstructure evolution of creep damaged DZ411 superalloy during rejuvenation heat treatment
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摘要: 采用固溶 + 二级时效工艺对蠕变损伤DZ411合金进行常规恢复热处理，研究蠕变损伤合金组织恢复演化过程，并评价其力学性能。结果表明：蠕变损伤的DZ411合金中的一次γ′相发生明显球化和筏化，二次γ′相消失，未发现晶界蠕变孔洞；固溶处理对于回溶粗大形变γ′相，并重新析出细小均匀分布的γ′相至关重要，同时选择合适的固溶温度可避免初熔和再结晶；两级时效处理是优化γ′相尺寸、形态和配比的关键步骤；恢复后可获得大体积分数、双尺寸形态γ′相组织，二次和三次γ′相平均有效直径分别约为0.38 μm和0.07 μm，其体积分数分别约为47.5%和6.5%；恢复态合金室温强度与原始态合金相近，但在980 ℃/220 MPa下的持久寿命和伸长率分别达到121 h和13%，略低于原始态合金性能水平。Abstract: The simple solution and aging treatment processes were adopted to rejuvenate the microstructure of creep damaged DZ411 superalloy. The microstructure evolution of superalloy during rejuvenation process was investigated by OM and SEM, and then the mechanical properties were evaluated by tensile and creep rupture tests. The results show that creep damaged superalloy obtained from interrupted test at the end of secondary stage of creep suffers from the spheroidization and rafting of the prime γ′ phase and vanishing of the secondary γ′ phase, but no creep cavities. It is also found that the solution treatment plays a prime role in dissolution of deformed γ′ phase, and then re-precipitation of fine γ′ phase. The proper solution temperature can effectively avoid incipient melting and recrystallization. The two stages of aging are the dominant procedures of optimizing the size, shape and volume ratio of bimodal size γ′ phase. By the appropriate rejuvenation schedule, the bimodal size γ′ particles with coarse secondary γ′ particles and fine tertiary γ′ particles can be obtained. The average diameters of bimodal size γ′ particles are about 0.38 μm and 0.07 μm, and the volume fraction are 47.5% and 6.5% respectively. Rejuvenation heat treatment can successfully recover the room temperature strength close to that of the original alloy. The creep rupture life and elongation of rejuvenated DZ411 superalloy under condition of 980 ℃/220 MPa are 121 h and 13%, these values are slightly lower than that of the original alloy.
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图 1 原始态DZ411合金微观组织 （a）枝晶和共晶；（b）一次和二次γ′相；（c）晶内条状和块状MC碳化物；（d）晶界颗粒状MC碳化物
Figure 1. Microstructures of virgin DZ411 alloy （a）dendritic and eutectic；（b）prime and secondary γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）particulate prime MC carbides on grain boundary
图 2 损伤态DZ411合金微观组织 （a）枝晶和共晶；（b）球化和筏化一次γ′相；（c）晶内条状和块状MC碳化物；（d）膜状晶界M23C6碳化物
Figure 2. Microstructures of creep damaged DZ411 alloy （a）dendritic and eutectic；（b）spheroidized and rafted prime γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）lightly film-like secondary M23C6 carbides at grain boundary
图 3 固溶态（固溶条件：1150 ℃/2 h/AC）DZ411合金微观组织 （a）枝晶和共晶；（b）一次和二次γ′相；（c）晶内条状和块状MC碳化物；（b）晶界轻微膜状M23C6碳化物
Figure 3. Microstructures of DZ411 alloy after solution treatment under condition of 1150 ℃/2 h/AC （a）dendritic and eutectic；（b）prime and secondary γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）lightly film-like secondary M23C6 carbides at grain boundary
图 5 固溶态（1240 ℃/2 h/AC）DZ411合金微观组织 （a）初熔和再结晶；（b）二次γ′相；（c）晶内条状和块状晶内MC；（d）晶界连续膜状M23C6
Figure 5. Microstructures of DZ411 alloy after solution treatment under condition of 1240 ℃/2 h/AC （a）incipient melting and recrystallization；（b）re-precipitated secondary γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）continuous film-like secondary M23C6 carbides at grain boundary
图 4 固溶态（固溶条件: 1220 ℃/2 h/AC）DZ411合金微观组织 （a）金相；（b）二次γ′相；（c）晶内条状和块状MC碳化物；（b）晶界轻微膜状M23C6碳化物
Figure 4. Microstructures of DZ411 alloy after full solution treatment under condition of 1220 ℃/2 h/AC （a）dendritic and eutectic；（b）re-precipitated secondary γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）lightly film-like secondary M23C6 carbides at grain boundary
图 6 固溶 + 一级时效态（1220 ℃/2 h/AC + 1121 ℃/2 h/AC）DZ411合金微观组织 （a）枝晶和共晶；（b）二次和三次γ′相；（c）晶内块状MC碳化物和细小γ′相区；（d）晶界轻微膜状晶界M23C6碳化物
Figure 6. Microstructures of DZ411 alloy after full solution treatment + one stage aging treatment under condition of 1220 ℃/2 h/AC + 1121 ℃/2 h/AC （a）dendritic and eutectic；（b）secondary and tertiary γ′ phase；（c）block-like prime MC carbides and fine γ′ phase zone around them in grain interiors；（d）lightly film-like secondary M23C6 carbides at grain boundary
图 7 固溶 + 二级时效态（1220 ℃/2 h/AC + 1121 ℃/2 h/AC + 843 ℃/24 h/AC）DZ411合金微观组织 （a）枝晶和共晶；（b）二次和三次γ′相；（c）晶内条状和块状MC碳化物；（d）晶界连续膜状M23C6碳化物
Figure 7. Microstructures of DZ411 alloy after full solution treatment + two stages aging treatment under condition of 1220 ℃/2 h/AC + 1121 ℃/2 h/AC + 843 ℃/24 h/AC （a）dendritic and eutectic；（b）secondary and tertiary γ′ phase；（c）strip-like and block-like prime MC carbides in grain interiors；（d）continuous film-like secondary M23C6 carbides at grain boundary
图 8 原始态、损伤态和恢复态合金的拉伸性能
Figure 8. Tensile properties of DZ411 alloy for virgin, damaged and rejuvenated states
图 9 980 ℃/220 MPa条件下原始态、损伤态和恢复态合金的高温持久性能
Figure 9. Creep rupture properties of DZ411 alloy under condition of 980 ℃/220 MPa for virgin, damaged and rejuvenated states
表 1 原始态、损伤态和恢复态DZ411合金中γ′相的平均直径和体积分数统计值
Table 1. Statistical average diameter and volume fraction of γ′ phase in DZ411 alloy for virgin, damaged and rejuvenated states
Condition Particle type Average diameter/μm Volume fraction/% Virgin alloy Primary γ′
Secondary γ′0.64 ± 0.06
0.11 ± 0.0250.3 ± 2.43
2.49 ± 0.08Damaged alloy Primary γ′
Secondary γ′0.80 ± 0.03
–37.5 ± 1.46
–Rejuvenated alloy Secondary γ′
Tertiary γ′0.38 ± 0.03
0.07 ± 0.0147.5 ± 0.2
6.5 ± 0.14
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