The figure on the left plots an index representing oxidation resistance on the vertical axis against creep rupture life at 1100°C/137 MPa on the horizontal axis. While the high-temperature strength of Ni-base single-crystal superalloys has improved with each successive generation, their oxidation resistance has tended to decline. Superalloys from the fifth generation onwards address this by incorporating a greater number of elements that enhance oxidation resistance—while maintaining high-temperature strength—and optimizing the balance between them. TMS-238 is a sixth-generation Ni-base single-crystal superalloy offering excellent high-temperature oxidation and creep strength characteristics; it is expected to see practical application as a high-pressure turbine blade in aircraft engines.
The figure on the right plots thermal fatigue characteristics on the vertical axis against creep rupture life at 1100°C/137 MPa on the horizontal axis. For power generation turbines, the addition of elements such as Re or Ru is considered undesirable due to manufacturing cost considerations. Consequently, TMS-1700—a low-cost Ni-based single-crystal superalloy offering excellent creep strength and thermal fatigue characteristics—was developed with a reduced content of the strengthening element Re. Verification testing is currently underway with a view toward practical application.