Advanced Alloy Design Program and Improvement of Sixth-Generation Ni-Base Single Crystal Superalloy TMS-238
This paper describes the advanced alloy design program (AADP) and improvement of a sixth-generation single crystal superalloy, TMS-238, using this AADP. Creep rupture life prediction equations for five different creep conditions, 800 °C/735 MPa, 900 °C/39
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Abstract
Introduction
This paper describes the advanced alloy design program (AADP) and improvement of a sixth-generation single crystal superalloy, TMS-238, using this AADP. Creep rupture life prediction equations for five different creep conditions, 800 °C/735 MPa, 900 °C/392 MPa, 1000 °C/245 MPa, 1100 °C/137 MPa, and 1150 °C/137 MPa, were obtained with excellent determination coefficients from 0.95 to 0.98. Using the AADP, we successfully developed three alloys, TMS-238mod-A, TMS-238mod-B, and TMS-23mod-C, which have 10– 22 °C higher-temperature capabilities than those of the TMS-238 alloy. The AADP successfully predicted that the creep life was maximized when the volume fraction of c′ phase was approximately 65% at low-temperature and high-stress conditions, such as 900 °C/392 MPa, compared to that of approximately 60% under hightemperature and low-stress conditions, such as 1100 ° C/137 MPa. This prediction enables us to precisely optimize the creep property. Moreover, the prediction equation of the weight change after 1100 °C/1 h oxidation was also updated. The determination coefficient of this equation was R2 = 0.90. Keywords
Alloy design Ni-base single crystal superalloys Creep Oxidation TMS-238
T. Yokokawa (&) H. Harada K. Kawagishi T. Kobayashi M. Yuyama Y. Takata National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan e-mail: [email protected]
Ni-base single crystal (SC) superalloys with superior mechanical properties are being developed to improve the thermal efficiency of jet engines and land-based gas turbines. We reported that a larger negative lattice misfit (ac > ac′) promotes the formation of the so-called raft structure of c/c′ phases [1, 2] with a finer interfacial dislocation network, which prevents dislocation gliding. Thus, it increases the creep resistances at higher-temperature and lower-stress conditions [3, 4]. We have developed SC superalloys with the world’s highest temperature capabilities using our in-house alloy design program (ADP), for example, the sixth-generation SC superalloy TMS-238 [5] with a temperature capability of 1120 °C, as shown in Fig. 1. This paper describes an advanced alloy design program (AADP) and an improvement of the TMS-238 alloy using this AADP.
Alloy Design Program The concept of an alloy design utilizing a computer program was first established in Japan in the 1970s [6, 7]. The alloy design enabled the search for the best candidate alloys before the experimental evaluation among numerous combinations of Ni-base superalloy compositions. Since then, ADP has been improved and utilized for alloy development of Ni-base superalloys [8, 9] and for the construction of a virtual gas turbine [10] stimulating the development of the 1700 °C-class gas turbine. Figure 2 shows a schematic flow chart of the ADP. The ADP is composed of two sub-programs; an analysis program and a search program. The analysis program is used to calculate the structural parameters and high-temperature properties from the alloy compo
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