Creep-resistant, cobalt-containing alloys for high temperature, liquid-salt heat exchanger systems
An essentially Fe-free alloy consists essentially of, in terms of weight percent: 4 to 11 Co, 6.5 to 7.5 Cr, 0 to 0.15 Al, 0.5 to 0.85 Mn, 11 to 20 Mo, 1 to 3.5 Ta, 0.05 to 9 W, 0.03 to 0.08 C, 0 to 0.001 B, 0.0005 to 0.005 N, balance Ni, the alloy being characterized by, at 850° C., a yield strength of at least 25 Ksi, a tensile strength of at least 45 Ksi, a creep rupture life at 12 Ksi of at least 10 hours, and a corrosion rate, expressed in weight loss [g/(cm 2 sec)]10 −11 during a 1000 hour immersion in liquid FLiNaK at 850° C., in the range of 5 to 20.
1. An alloy consisting essentially of, in terms of weight percent, a mixture of:
Co 4 to 11
Cr 6.5 to 7.5
Al 0 to 0.15
Mn 0.5 to 0.85
Mo 11 to 20
Ta 1 to 3.5
W 0.05 to 9
C 0.03 to 0.08
B 0 to 0.001
N 0.0005 to 0.005
Ni balance
said alloy being devoid of γ′ precipitates and devoid of γ′ precipitate hardening, and being essentially iron free and characterized by, at 850° C., a yield strength of at least 25 Ksi, a tensile strength of at least 45 Ksi, a creep rupture life at 12 Ksi of at least 10 hours, and a corrosion rate, expressed in weight loss [g/(cm 2 sec)]10 −11 during a 1000 hour immersion in liquid FLiNaK at 850° C., in the range of 5 to 20, wherein said alloy is further characterized by a corrosion susceptibility index of no less than about 0.06 and no more than about 0.115.
2. An alloy in accordance with claim 1 wherein the range of Co is 4.5 to 10.5 weight percent.
3. An alloy in accordance with claim 1 wherein the range of Cr is 6.7 to 7.1 weight percent.
4. An alloy in accordance with claim 1 wherein the range of Al is 0.05 to 0.12 weight percent.
5. An alloy in accordance with claim 1 wherein the range of Mn is 0.7 to 0.83 weight percent.
6. An alloy in accordance with claim 1 wherein the range of Mo is 11.5 to 19 weight percent.
7. An alloy in accordance with claim 1 wherein the range of Ta is 1.4 to 3.1 weight percent.
8. An alloy in accordance with claim 1 wherein the range of C is 0.04 to 0.07 weight percent.
9. An alloy in accordance with claim 1 wherein said yield strength is at least 29 Ksi.
10. An alloy in accordance with claim 1 wherein said tensile strength is at least 49 Ksi.
11. An alloy in accordance with claim 1 wherein said creep rupture life is at least 15 hours.
12. An alloy in accordance with claim 1 wherein said corrosion rate is no more than 18.5.
13. An alloy in accordance with claim 1 , wherein the alloy is solid solution strengthened.