Effect of Ir on the microstructural stability of the 6th generation Ni-base single crystal superalloy, TMS-238

Abstract

Alloy development for turbine blade materials with higher temperature capabilities is crucial in order to improve the thermal efficiency in jet engines and gas turbine systems. The 6 th generation Ni-base single crystal (SC) superalloy, TMS-238, developed by NIMS has a good microstructure stability and 1120°C temperature capability (1000 hours creep rupture life under stress of 137 MPa). In the previous studies, we investigated the influence of alloying elements on microstructure and creep strength of TMS-238 to improve the temperature capability of this alloy. The rupture life of TMS-238 + ReRu alloy which had increased Re and Ru concentrations based on TMS-238 was three times longer than TMS-238 under the condition of 1150°C-137 MPa. In the case of 1000°C and 900°C and at higher stresses conditions, however, rupture lives of TMS-238 + ReRu alloy were shorter than TMS-238 due to fine TCP phase precipitation during creep test. In this study, we examined effect of substituting Ru with Ir in TMS-238 + ReRu to improve the stability of γ-γ' two-phases microstructure and the creep strengths. As a result, the rupture life of TMS-238 + Relr was longer than TMS-238 + ReRu under the condition of 900°C-392 MPa. This is due to suppression of fine TCP phase precipitation and the solution strengthening of Ir. In the case of 1150°C-137 MPa, the rupture life of TMS-238+Relr was shorter than TMS-238 + ReRu but longer than TMS-238.