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利用团簇成分式方法设计系列低密度Co基高温合金[Al-(Co 8Ni 4)]((Al 0.5(Ti/Nb/Ta) 0.5Mo 0.5) (Mo 0.5Cr 0.5Co 0.5))(=Co 8.5Ni 4Al 1.5Mo 1.0Cr 0.5(Ti/Nb/Ta) 0.5), 采用真空非自耗电弧炉制备合金铸锭, 并对其在1300 ℃固溶15 h , 在900 ℃下进行长期时效处理, 进而对时效态样品进行微观组织表征和力学性能测试. 结果表明, 当Ti/Nb/Ta, Ti/Nb和Ti/Ta以等物质的量比匹配时, 3种合金的微观组织均表现为立方形γ′相均匀地分布在γ基体中, 这取决于合金适中的γ/γ′点阵错配度(0.27%—0.34%). 在900 ℃长期时效过程中, 3种合金中的γ′相均具有较小的粗化速率, 且合金的显微硬度随时效时间基本不发生变化(275—296 HV); 尤其(Ti/Ta) 0.5合金具有最高的 γ/ γ′共格组织稳定性, 时效500 h后 γ′相粗化最慢, 并在晶界处无其他第二相粒子析出, 而在其他合金的晶界附近均析出针状和颗粒状的第二相粒子.Co-base superalloys generally have high strengths, good oxidation- and corrosion-resistances, as well as excellent creep-resistant properties at high temperatures (HTs), which are ascribed to the coherent precipitation of cuboidal γ′phase into face-centered-cubic (FCC) γmatrix induced by co-alloying of multiple elements. However, the cuboidal γ/ γ′coherent microstructure is liable to be destabilized after a long-time aging at HTs in Co-base superalloys. In the present work, the cluster formula is used to design a series of low-density Co-base superalloys with the composition of [Al-(Co 8Ni 4)]((Al 0.5(Ti/Nb/Ta) 0.5Mo 0.5)(Mo 0.5Cr 0.5Co 0.5)) (=Co 8.5Ni 4Al 1.5Mo 1.0Cr 0.5(Ti/Nb/Ta) 0.5). Alloy ingots are prepared by arc melting under an argon atmosphere, and are solid-solutionized at 1300 ℃ for 15 h and then aged at 900 ℃ for up to 500 h. Microstructural characterizations and mechanical properties of these alloys in different aged states are obtained by using XRD, SEM, EPMA, TEM, and HV. It is found that all these alloys with Ti/Nb/Ta, Ti/Nb, and Ti/Ta in an equi-molar mixing have a special coherent microstructure with cuboidal γ′phase uniformly-precipitated into the γ matrix, which is contributed to the moderate lattice misfit of γ/ γ′(0.27%–0.34%). Moreover, these cuboidal γ′phase are coarsened slowly during aging, in which the microhardness does not vary obviously with aging time (275 HV–296 HV). Especially, the alloy with (Ti/Ta) 0.5exhibits the highest γ/ γ′microstructural stability with a slow coarsening rate after aging 500 h, and no other second phases appear near the grain boundaries. While needle and bulk particles would precipitate on grain boundaries in other alloys after 500 h-aging.
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Keywords:
- Co-base superalloys/
- coherent microstructure/
- γ′phase coarsening/
- the second precipitated phases
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Alloy Cluster formulas Alloy composition/% a/nm ε/% S1-TNT [Al-(Co8Ni4)]((Al0.5(Ti, Nb, Ta)0.5Mo0.5)(Mo0.5Cr0.5Co0.5)) Co53.13Ni25.00Al9.38Ti1.04Nb1.04Ta1.04Cr3.12Mo6.25 aγ= 0.3570 ± 0.0003
aγ′= 0.3583 ± 0.00020.34 ± 0.05 S2-TN [Al-(Co8Ni4)]((Al0.5(Ti, Nb)0.5Mo0.5)(Mo0.5Cr0.5Co0.5)) Co53.13Ni25.00Al9.38Ti1.56Nb1.56Cr3.12Mo6.25 aγ= 0.3575 ± 0.0004
aγ′= 0.3584 ± 0.00020.27 ± 0.05 S3-TT [Al-(Co8Ni4)]((Al0.5(Ti, Ta)0.5Mo0.5)(Mo0.5Cr0.5Co0.5)) Co53.13Ni25.00Al9.38Ti1.56Ta1.56Cr3.12Mo6.25 aγ= 0.3575 ± 0.0004
aγ′= 0.3586 ± 0.00030.29 ± 0.07 
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41]
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