Our Ni-base single crystal (SC) superalloys that have been designated as 4th and 5th generation SC alloys contain Ru for the enhancement of microstructure stability. The authors have previously reported that Ir addition was as effective as Ru for enhancing the microstructure stability.
In this paper, Ir was added to TMS-173, a new 5th generation SC alloy, by substituting out Ru. The creep strength of this new SC alloy, designated as TMS-173(Ir), was then compared to that of the original Ru-containing alloys, TMS-173. Creep tests were conducted for these SC superalloys under several conditions: 800°C/735 MPa, 900°C/392 MPa, 1000°C/245 MPa and 1100°C/137 MPa. The Ir-containing alloys showed shorter creep rupture life than The Ru-containing one in higher temperature and lower stress conditions such as 1100°C/137 MPa. However, at lower temperature and higher stress conditions, The Ir-containing alloy showed longer creep rupture life than Ru-containing one; the former showed 3.2 times longer creep rupture life than the latter in the creep tests at 900°C/392 MPa. Microstructure observations of creep-ruptured specimens confirmed that Ir was as effective as Ru for microstructure stability.