Patent Application
20080008618
Although Co expands the solution heat treatment temperature range, when the content thereof is less than 9 wt % (for the third alloy, 10 wt %), the effect cannot be obtained, and when it is more than 11 wt % (for the second alloy, 10 wt %), the deposition of the γ″ phase is reduced and the high-temperature strength is lowered.
Although Cr particularly improves the resistance to corrosion in a multiple environment of sulfidation and oxidation, when the content thereof is less than 9 wt % (for the third alloy, 10 wt %), the effect cannot be obtained and when it is more than 12 wt % (for the second alloy, 10 wt %), a TCP (Topologically Close Packed) phase is generated and the high-temperature strength is lowered.
Although Mo improves the high-temperature strength by solid solution reinforcement and deposition hardening, when the content thereof is more than 1 wt %, the resistance to corrosion is lowered.
Further, the second alloy, when the content of Mo is less than 0.5 wt %, cannot obtain the aforementioned effect.
Although W improves the high-temperature strength by solid solution reinforcement and deposition hardening, when the content thereof is less than 6 wt % (for the third alloy, 8 wt %), the effect cannot be obtained, and when it is more than 9 wt % (for the second alloy, 8 wt %), the TCP phase is generated and the high-temperature strength is lowered.
Further, although W is generally considered to lower the resistance to corrosion, knowledge that in the composition area of the present invention, there is few effect by W on the resistance to corrosion is obtained.
Although Al generates the γ′ phase and improves the high-temperature strength and resistance to oxidation, when the content thereof is less than 4 wt %, the effect cannot be obtained, and when it is more than 5 wt %, the eutectic γ′ phase is increased in amount, and the solution heat treatment becomes difficult to be performed, and the resistance to corrosion is lowered.
Although Ti improves the resistance to corrosion, when the content thereof is less than 4 wt %, the effect cannot be obtained, and when it is more than 5 wt %, the resistance to oxidation is lowered, and the heat treatment property is lowered.
Although Nb is fused in the γ′ phase and improves the high-temperature strength, when the content thereof is more than 1 wt %, it is deposited in the grain boundaries, and lowers the high-temperature strength.
Although Ta improves the high-temperature strength by solid solution reinforcement and deposition hardening, when the content thereof is more than 3 wt %, the eutectic γ′ phase is increased in amount, and the solution heat treatment becomes difficult to be performed.
Further, the second alloy, when the content of Ta is less than 2 wt %, cannot obtain the aforementioned effect.
Although Hf reinforces the grain boundaries and improves the high-temperature strength and ductility and is effective to prevent intergranular cracking during DS casting, when the content thereof is less than 0.5 wt %, the effect cannot be obtained, and when it is more than 2.5 wt %, it segregates in the grain boundaries, and lowers the high-temperature strength.
Although Re improves the high-temperature strength by solid solution reinforcement and particularly improves the resistance to corrosion at 900° C. or higher, when the content thereof is more than 3 wt %, the ductility is deteriorated by deposition of the TCP phase, and the specific gravity is increased, and the cost is increased.
Further, the second alloy cannot obtain the aforementioned effect when the content of Re is less than 1 wt %.
Although C forms carbides and reinforces the grain boundaries, when the content thereof is less than 0.05 wt %, the effect cannot be obtained, and when it is more than 0.15 wt % (for the second alloy, 0.1 wt %), an excessive carbide is generated, and the high-temperature strength is lowered.
Although B forms boronides and reinforces the grain boundaries, when the content thereof is less than 0.005 wt %, the effect cannot be obtained, and when it is more than 0.015 wt % (for the second alloy, 0.01 wt %), the ductility and toughness are lowered, and the high-temperature strength is lowered.
Although Zr reinforces the grain boundaries, when the content thereof is more than 0.05 wt % (for the second alloy, 0.02 wt %), the ductility and toughness are lowered, and the high-temperature strength is lowered.
Further, the third alloy cannot obtain the aforementioned effect when the content of Zr is less than 0.01 wt %.
Ni-base superalloys (alloys 1 to 3 of the present invention and comparison alloys 1 to 3) having the component composition shown in Table 1 (the component compositions of the existing alloy 1 (Rene80H) and existing alloy 2 (Mar-M247) are also shown) are prepared, and these Ni-base superalloys are solidified under the condition of withdrawing speed 200 mm/h using a directional solidification casting furnace, and columnar crystalline castings are manufactured.
Next, the heat treatment indicated below is performed, thus the respective Ni-base superalloys are obtained.
Heat treatment conditions
Solution treatment: At 1200 to 1260° C., holding for 2 hours, then air cooling
Aging: First stage, at 1080° C., holding for 4 hours, then air cooling
For the test specimens of the alloys 1 to 3 of the present invention obtained and the existing alloys 1 and 2, the hot corrosion test is executed under the following conditions and the maximum corrosion depth of each test specimen obtained is shown in
Test specimen shape: Diameter of 10 mm, length of 100 mm
Test conditions: In combustion gas with corrosive ingredients (sulfuric oil, artificial seawater) added into kerosene fuel, at a combustion gas temperature of 1050° C., air cooling after exposure for 100 hours, repeated 5 times (500 hours in total)
Further, for the test specimens of the alloys 1 to 3 of the present invention obtained and the existing alloys 1 and 2, the oxidation test is executed under the following conditions and the mass change of each test specimen obtained is shown in
Test specimen shape: Diameter of 10 mm, length of 25 mm
Test conditions: In the atmosphere, at 950° C., air cooling after exposure for 500 hours
Furthermore, for the test specimens of the alloys 1 to 3 of the present invention obtained and the existing alloys 1 and 2, the creep test is executed under the following conditions and the rupture life of each test specimen obtained is shown in
Test specimen shape: Diameter of 4 mm, gauge length of 24 mm
Test conditions: In the atmosphere, at 900° C., at 392 MPa
On the basis of the existing alloy 1, the maximum corrosion depth ratio in the hot corrosion test, the mass change ratio in the oxidation test, and the rupture life ratio in the creep test for the alloys 1 to 3 of the present invention, the comparison alloys 1 to 3, and the existing alloy 2 are checked and the results are shown in Table 2.
As shown in
The alloy 2 of the present invention is suited to use under the condition that the resistance to oxidation and strength are needed, and the resistance to corrosion is within the tolerance to use the heavy oil fuel.
Further, the alloy 3 of the present invention is suited to use under the condition that the resistance to corrosion is needed.
Although the existing alloy 1 is widely used as a turbine blade material of a gas turbine and is excellent in the resistance corrosion, as compared with the composition range of the alloys 1 to 3 of the present invention, it contains much Cr and little Al, so that the resistance to oxidation is low, thus the existing alloy 1 cannot deal with high-temperature demands of combustion gas aiming at improvement of thermal efficiency.
Further, although the existing alloy 2 is excellent in the resistance to oxidation and strength, as compared with the composition range of the alloys 1 to 3 of the present invention, it contains little Cr and Ti and much Al, so that the resistance to corrosion is low, thus the existing alloy 2 cannot deal with heavy oil fuel.
The comparison alloy 1 (almost corresponding to the composition range described in Japanese Patent Laid-Open Publication No. 5-59473 and Japanese Patent Laid-Open Publication No. 9-170402), as compared with the composition range of the alloys 1 to 3 of the present invention, contains little Ti, so that the resistance to corrosion is insufficient.
The comparison alloy 2 (almost corresponding to the composition range described in Japanese Patent Laid-Open Publication No. 9-170402), as compared with the composition range of the alloys 1 to 3 of the present invention, contains much Cr and little Al and W, so that the strength is insufficient.
Further, the comparison alloy 3 (almost corresponding to the composition range described in Japanese Patent Laid-Open Publication No. 5-59473), as compared with the composition range of the alloys 1 to 3 of the present invention, contains much Mo, so that the resistance to corrosion is insufficient.
Although the invention has been described in its preferred embodiment with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-435037 | Dec 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/19094 | 12/21/2004 | WO | 00 | 8/17/2006 |
