Development of novel Ni-based single crystal superalloys for power-generation gas turbines

Abstract

In advanced industrial gas-turbine systems, there has been a great demand for new single crystal (SC) superalloys with an excellent combination of high-temperature creep strength, hot-corrosion resistance and oxidation resistance. In this study, 12 nickel-based SC superalloys were designed with the aid of the d-electrons concept. Their chemical compositions were in the range of 1.2–1.5%Ti, 3.8–6.5%Cr, 11%Co, 0–1.4%Mo, 0–3.0%Ru, 6.5–7.4%Ta, 5.0–6.4%W, 3.6–5.4%Re, 5.1–5.5%Al, 0.12–0.14%Hf and balanced Ni in wt%. A series of experiments such as creep rupture tests, burner rig tests and cyclic oxidation tests were conducted with the heat-treated SC specimens of these alloys. Almost all the designed alloys were found to be superior in creep rupture life to a second generation superalloy currently used in the world. For hot-corrosion resistance, estimated from the burner rig tests, any of the designed alloys were comparable or even superior to a second generation superalloy. The oxidation resistance was very different among the designed alloys, but some of them showed better resistance than the second generation superalloy. Thus the SC alloys containing about 4–5 wt%Re had about 30°C or more higher temperature capability than the second generation superalloy, while exhibiting excellent hot-corrosion resistance and good oxidation resistance.