Abstract: The effects of the melt superheating treatment on the microstructure and mechanical properties of a cast nickel-base superalloy were investigated. A large amount of coarse or needle-like carbides within the grain interior or at grain boundary in this alloy as conventional cast, is very harmful to the mechanical properties. It is suggested that the melt superheating treatment at high temperature can be conducive to the improvement of the ductility of the alloy. The results show that the microstructure of the alloy can be significantly influenced by the melt superheating treatment, that is, the dendritic structure is refined, and the amount of carbides is reduced. Consequently, after treated at 1650℃ for 5min, tensile ductility of cast alloy is increased remarkably from 3.5% to 9.2% at room temperature, from 2.0% to 8.0% at 700℃ and from 2.4% to 9.6% at 900℃, respectively, without loss of its high strength. Meanwhile, the creep life of superalloy lower than 225MPa at 975℃ is also improved obviously.
Effect of melt superheating treatment on microstructure and mechanical properties of cast nickel-base superalloy
Abstract:
The effects of the melt superheating treatment on the microstructure and mechanical properties of a cast nickel-base superalloy were investigated. A large amount of coarse or needle-like carbides within the grain interior or at grain boundary in this alloy as conventional cast, is very harmful to the mechanical properties. It is suggested that the melt superheating treatment at high temperature can be conducive to the improvement of the ductility of the alloy. The results show that the microstructure of the alloy can be significantly influenced by the melt superheating treatment, that is, the dendritic structure is refined, and the amount of carbides is reduced. Consequently, after treated at 1 650 ℃ for 5 min, tensile ductility of cast alloy is increased remarkably from 3.5% to 9.2% at room temperature, from 2.0% to 8.0% at 700 ℃ and from 2.4% to 9.6% at 900 ℃, respectively, without loss of its high strength. Meanwhile, the creep life of superalloy lower than 225 MPa at 975 ℃ is also improved obviously.
表3 实验合金经不同温度精炼处理后室温及高温的拉伸性能 Table 3 Tensile properties at room temperatureand high temperature of test superalloy treatedat different superheting temperatures
Treatment
Testing temperature/ ℃
σb/ MPa
σ0.2/ MPa
δ/ %
ψ/ %
Conventional
Room temperature
1 128
1 016
3.5
700
969
904
2.0
900
819
690
2.8
Teatment 1
Room temperature
979
806
8.0
12.1
700
1 066
853
8.0
10.4
900
801
680
4.4
6.1
Teatment 2
Room temperature
1 038
851
9.2
11.7
700
1 078
860
8.0
11.5
900
832
681
9.6
19.6
Teatment 3
Room temperature
998
784
6.4
14.0
700
1 041
857
9.6
16.9
900
781
657
7.6
11.3
图2 高温精炼温度对实验合金在975 ℃, 225 MPa应力下蠕变曲线的影响 Fig.2 Effects of melt superheating temperature on creep behavior of test superalloy at 975 ℃ under 225 MPa
表4 实验合金在1 600 ℃经不同时间高温精炼处理后的高温拉伸和持久性能 Table 4 High temperature tensile and stress-rupture properties of test superalloy treated at1600 ℃ for different melt superheating durations