Papers by Keyword: Ni-Based Single Crystal Superalloy

Abstract: Steam oxidation behavior of a new Ni-based single crystalline superalloy (TMS-75) developed as the high strength material for the advanced gas turbine which would be cooled by steam was studied in comparison with Inconel 625 alloy which is a representative Ni based superalloy and 12Cr ferritic steel which is conventionally used in boiler tubes and main steam pipes and steam turbines. TMS-75 alloy showed worse oxidation resistance in steam than Inconel 625 alloy, but it had much better oxidation resistance in steam than 12Cr steel. Also, the oxide scale of Inconel 625 alloy is very thin and is mainly composed of Cr2O3. However, the outer scale of TMS- 75 alloy was mainly composed of NiO with Co and a little Al and other elements. The Ni/Co ratio in the oxide scale was a little higher in the outer layer than in the inner layer.

Abstract: Ni-base single crystal (SC) superalloys containing high concentrations of refractory elements are prone to generate a diffusion layer called Secondary Reaction Zone (SRZ) beneath their bond coating during exposure at high temperatures. SRZ causes a reduction of the load bearing cross section and is detrimental to the creep properties of thin-wall turbine airfoils. In this study, a new coating system – “EQ coating”, which is in thermodynamic equilibrium with the substrate, has been proposed and the formation behavior of SRZ beneath bond coat materials was investigated on the 5th generation Ni-base SC superalloy developed by NIMS. Diffusion couples of several alloys were made and were heat treated at 1100°C for 300 h, 1000 h. The concentration profiles were analyzed by EPMA. Also, cyclic oxidation tests were carried out at 1100°C in air.