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摘要: 采用气淬炉模拟了粉末高温合金Udimet720Li经空冷、风冷及油冷等不同冷却路径的固溶处理过程，测试了经过两级时效处理的合金在650 ℃的拉伸性能，研究了拉伸变形后的位错组态，分析了冷却速率对γ′强化相析出规律及力学性能的影响。结果表明：粉末高温合金Udimet720Li的析出相强化机制为位错切过机制，二次γ′相尺寸越小，合金强度越高。合金二次γ′相的形核析出温度区间为900～1000 ℃，其尺寸与合金在该温度范围内的冷却速率成反比，冷却速率越大，γ′相尺寸越小，当冷速高于100 ℃/min时，合金强度达到应用要求。推荐粉末Udimet720Li合金盘件固溶处理的冷却方式为：在1000 ℃以上保持低冷却速率来降低淬火应力，然后选择油浴作为盘件淬火的冷却方式，入油温度应在1000 ℃左右。Abstract: P/M superalloy Udimet720Li specimens were solutioned and quenched at the different cooling rates in gas quenching furnace, following by the double aging treatment. The microstructures and elevated temperature tensile properties at 650 ℃ were investigated, and the γ′ precipitation behavior and strengthening mechanism were analysed. The effect of cooling rates on the microstructures and properties of γ′ phase were discussed. Results show that the secondary γ′ phases mainly precipitate between 900 ℃ and 1000 ℃ for the P/M superalloy Udimet720Li, and the size of the secondary γ′ phases are inversely proportional to the cooling rates. The secondary γ′ phase interacts with the dislocations by shearing mechanism, enhancing the strength of P/M superalloy Udimet720Li. The strengthening effect increases with the decrease of the secondary γ′ phase size. To meet the strength requirement in practical application, the cooling rate should be more than 100 ℃/min. Therefore, the recommended solution cooling path for P/M superalloy Udimet720Li is shown as follow: the cooling rate should be slow to reduce the quenching stress above 1000 ℃, then the specimen can be quenched in oil at 1000 ℃ to obtain enough strength.
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Key words:
- P/M superalloy /
- cooling rate /
- strengthening phase /
- mechanical property /
- solution treatment
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图 2 两级时效处理后的粉末高温合金Udimet720Li试样晶粒组织：（a）试样1；（b）试样2；（c）试样3；（d）试样4；（e）试样5
Figure 2. Grain structures of the P/M Udimet720Li specimens experiencing the double aging treatment: (a) specimen 1; (b) specimen 2; (c) specimen 3; (d) specimen 4; (e) specimen 5
图 3 两级时效处理后的粉末高温合金Udimet720Li试样γ′相组织：（a）试样1；（b）试样2；（c）试样3；（d）试样4；（e）试样5
Figure 3. γ′ morphologies of the P/M Udimet720Li specimens experiencing the double aging treatment: (a) specimen 1; (b) specimen 2; (c) specimen 3; (d) specimen 4; (e) specimen 5
图 4 二次γ′相平均尺寸随冷却速率的变化关系
Figure 4. Average size of the secondary γ′ phases with the cooling rate
图 5 屈服强度与γ′相平均尺寸间的关系
Figure 5. Yield strength with the average size of the secondary γ′ phases
图 6 粉末高温合金Udimet720Li试样1（1100 ℃→500 ℃，冷却速率30 ℃/min）拉伸变形后显微组织
Figure 6. TEM images of the P/M Udimet720Li alloy specimens (1100 ℃→500 ℃, cooling rate: 30 ℃/min) after tensile deformation
图 7 粉末高温合金Udimet720Li试样1（1100 ℃→500 ℃，冷却速率30 ℃/min）拉伸变形后的位错组态
Figure 7. Dislocation configuration of the P/M Udimet720Li alloy specimens (1100 ℃→500 ℃, cooling rate: 30 ℃/min) after tensile deformation
表 1 粉末高温合金Udimet720Li名义成分（质量分数）
Table 1. Nominal composition of the P/M Udimet720Li alloys
% Cr Co Al Ti W Mo Zr B C Ni 16.000 14.750 2.500 5.000 1.250 3.000 0.035 0.020 0.015 余量 
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表 2 粉末高温合金Udimet720Li试样冷却路径
Table 2. Cooling paths of the P/M Udimet720Li specimens
试样编号 冷却路径 1 以30 ℃/min的速率从1100 ℃冷却至500 ℃ 2 以100 ℃/min的速率从1100 ℃冷却至500 ℃ 3 以250 ℃/min的速率从1100 ℃冷却至500 ℃ 4 以100 ℃/min的速率从1100 ℃冷却至1000 ℃，再以250 ℃/min的速率从1000 ℃冷却至500 ℃ 5 以100 ℃/min的速率从1100 ℃冷却至900 ℃，再以250 ℃/min的速率从900 ℃冷却至500 ℃
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表 3 两级时效处理后的粉末高温合金Udimet720Li试样γ′相尺寸及含量（体积分数）
Table 3. γ′ size and volume fraction of the P/M Udimet720Li specimens experiencing the double aging treatment
试样编号 二次γ′相平均尺寸 / nm 二次γ′相含量，
体积分数 / %1 149.7 48 2 127.8 45 3 87.7 47 4 90.3 46 5 131.2 44
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表 4 两级时效处理后的粉末高温合金Udimet720Li试样的650 ℃拉伸性能
Table 4. Tensile properties of the P/M Udimet720Li specimens experiencing the double aging treatment at 650 ℃
试样编号 Rm / MPa Rp / MPa A / % Z / % 1 1282 980 35 35 2 1354 1041 30 34 3 1375 1091 28 30 4 1382 1095 24 24 5 1369 1037 27 28 注：Rm为抗拉强度；Rp为屈服强度；A为断后伸长率；Z为断面收缩率。
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