Toshihiro Yamagata, Shizuo Nakazawa, Yutaka Koizumi,
Toshiharu Kobayashi, Masahiro Sato, Takehisa Hino, Norio Shibasaki
Ni-base Superalloy Team, High Temperature Materials 21 Project
National Research Institute for Metals
1-2-1 Sengen, Tsukuba Science City, 305-0047
Japan
The Ni-base Superalloy Team is in charge of developing new single crystal (SC) and directionally solidified (DS) superalloys. The developed alloys are to be brought into actual practical use as turbine blades to realise high efficiency industrial gas turbines and advanced aeroengines. The development target is set at 1100(C as temperature capability under 137MPa and 1000h creep rupture life. Some collaborations have started with Japanese private companies expecting turbine tests with using developed superalloys.
A third generation SC superalloy TMS-75 [1,2], Ni-12Co-3Cr-2Mo-6W-6Al-6Ta-0.1Hf-5Re, wt%, was previously developed by us using NRIM Alloy Design Program[3] with help of Cluster Variation Method [4]. This alloy is more stable in microstructure than CMSX-10 [5] and also easier to do heat treatment due to the wide heat treatment window. The creep strength is equivalent with CMSX-10.
Considering these properties, in this project, we try to apply this alloy to blade material in industrial gas turbines. Under collaboration with Toshiba PIC, a 15 MW class gas turbine blades were successfully cast and heat treated as Fig.1. The blades are to be machined and tested in an actual 15 MW gas turbine to prove its excellent high temperature properties. The test is scheduled to start in October 2000. This would be the first industrial gas turbine test ever done with a third generation SC superalloy.
For even larger gas turbines, the materials cost may be considered more seriously. Thus designed under collaboration with Toshiba PIC is an SC superalloy TMS-82 [6,7], which contains 2.4 wt% Re, a half of that in TMS-75 and other third generation superalloys. At higher temperature and lower stress conditions, the creep strength of TMS-82 is superior to CMSX-10 and even Ru containing alloy appeared in US patent [8].
In this project, again we try to test this high cost performance SC alloy, as a first stage blade of the 15 MW gas turbine.
For small gas turbines of about 1 to 8 MW class, DS superalloys are mainly used. Under a previous collaboration with Kawasaki Heavy Industries, we developed a third generation DS superalloy, TMD-103 [9], the first third generation DS alloy ever published in the world. The creep strength is exactly the same as the second generation SC superalloy, CMSX-4.
In this project, having the results above, we are testing TMD-103 in terms of long term creep properties, hot corrosion resistance, etc. to evaluate its potential for the small gas turbine blades [10]. The results will be presented.
Small gas turbines may have more chance to be driven by rather low quality oil. For this reason, blade materials must have good hot corrosion resistance. In this project we also have designed a series of DS superalloys to have high hot corrosion resistance as well as creep strength. A burner rig hot corrosion test with these alloys is scheduled in this fiscal year.
At least two approaches have been tried based on SC TMS-75 towards the fourth generation superalloys development.
Effects of Pt group metals single additions on microstructure and creep properties were examined. Ir, Ru, Pt, Rh, and Pd were simply added by 1 at% to TMS-75. The creep results of the five alloys at 900(C and at 392MPa, the Pt group metals additions reduced the creep strength except for Ir. Fig. 2 shows the creep curve obtained at 1100(C and at 7.8MPa. At such high temperature and long term testing, Ir addition is effective. This is presumably due to the microstructure stability improved by Ir addition [1] as well as the possible reduction of diffusibity by the Ir addition. Hot corrosion resistance of the alloys are also investigated to clarify the effects of platinum group metals addition.
Another approach is to examine the effects of fundamental structural parameters by small ordinary alloying additions. For example, an increase in volume fraction of γ'phase by adding Al resulted in increase in creep strength at 900(C but not at 1100(C. At a high temperature (and a low stress), e.g., at 1100(C, and at 137MPa, alloying additions to bring lattice misfit more negative (aγ'< aγ) were found effective. This is understood that enhanced rafting with finer interfacial dislocation network is preventing the dislocation climbing effectively.
First cooling blades made of conventionally cast Rene'80 and used up to 15000h in a civil aeroengine were provided by an airline company and being examined. From the microstructural change in the blade, actual temperature distribution is going to be estimated. The results will be utilised for design of new superalloys and also for establishing the virtual gas turbine in this Project.
According to the total plan, we continue to develop the fourth generation SC alloy. Also we will evaluate the third generation superalloy TMS-75 expecting its practical applications as turbine blades and vanes. Linkages with some gas turbine projects under MITI are to be strengthened. Also, we are becoming ready to distribute TMS-75 SC bars for those interested in testing.
Some more collaborations with Japanese and overseas private companies are scheduled in the field of aeroengines and land based gas turbines. Also with some Japanese and overseas universities smaller scale fundamental collaborative researches are planed.
We thank Dr Yomei Yoshioka of Tosiba PIC and his colleagues for the invaluable collaboration work for the turbine test, etc. Also we thank Dr. Junzo Fujioka and Dr Akira Tamura and their colleagues of Kawasaki Heavy Industries for their invaluable collaboration for DS alloy development.
[1] T.Kobayashi, Y.Koizumi, S.Nakazawa, T.Yamagata, H.Harada, Proc. of the 4th International Charles Parsons Turbine Conference, 4-6 November 1997, Newcastle upon Tyne, UK, 766-773.
[2] Y.Koizumi, T.Kobayashi, T.Yokokawa, T.Kimura, M.Osawa, H.Harada, "Third Generation Single Crystal Superalloys with Excellent Processability and Phase Stability", Cost Conf. Liege, Part 2, 1998, 1089-1098.
[3] H.Harada, K.Ohno, T.Yamagata, T.Yokokawa, M.Yamazaki, Superalloys 1988, TMS AIME, 733.
[4] M.Enomoto, H.Harada, M.Yamazaki, CALPHAD, 1991,Vol.15,145.
[5] G.L.Erickson, Superalloys 1996, TMS, 35.
[6] T.Hino, Y.Ishiwata, Y.Yoshioka, K.Nagata, T.Kobayashi, Y.Koizumi, H.Harada, T.Yamagata, Proc. of the International Gas Turbine Congress 1999 Kobe, Nov. 14-19, 1999, 169-174.
[7] T.Hino, T.Kobayashi, Y.Koizumi, H.Harada, T.Yamagata, Superalloys 2000, TMS, submitted.
[8] K.S.O'hara, US-patent 5,482,789.
[9] T.Kobayashi, Y.Koizumi, H.Harada, T.Yamagata, A.Tamura, S.Nitta, Proc. of the 6th Liege Conference, Part 2, 1998, 1079-1087.
[10] T.Kobayashi, M.Sato, Y.Koizumi, H.Harada, T.Yamagata, A.Tamura, S.Nitta Superalloys 2000, TMS, submitted.