Abstract. Alloy718 has been used for many years in the aerospace industry due to its unique mechanical properties and good processing characteristics, especially its workability. However, the temperature limit of Alloy718 is about 650• C because of the thermal instability of the main strengthening phase γ -Ni 3 (Nb,Ti,Al). Numerous attempts have been made to develop a new wrought 718-type alloy for high temperature applications. The approach was to increase the stability, i.e. the solvus temperature of the γ -phase (T γ ,s ). However, this affected workability as the solvus temperature of the δ-phase (T δ,s ) did not increase accordingly so that the window for fine grain forging T δ,s -T γ ,s became smaller. In this paper the development of a new γ /γ -alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800• C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650• C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the δ-phase, allowing for solvus temperatures in excess of 1100• C. Consequently, the stability of the γ -phase can be increased by further addition of aluminium. At the same time the Ti-content is reduced to prevent formation of the η-(Ni,Co) 3 (Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.
Alloy718 has been used for many years in the aerospace industry due to its unique mechanical properties and good processing characteristics, especially its workability. However, the temperature limit of Alloy718 is about 650 • C because of the thermal instability of the main strengthening phase γ -Ni 3 (Nb,Ti,Al). Numerous attempts have been made to develop a new wrought 718-type alloy for high temperature applications. The approach was to increase the stability, i.e. the solvus temperature of the γ -phase (T γ ,s ). However, this affected workability as the solvus temperature of the δ-phase (T δ,s ) did not increase accordingly so that the window for fine grain forging T δ,s -T γ ,s became smaller. In this paper the development of a new γ /γ -alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800 • C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650 • C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the δ-phase, allowing for solvus temperatures in excess of 1100 • C. Consequently, the stability of the γ -phase can be increased by further addition of aluminium. At the same time the Ti-content is reduced to prevent formation of the η-(Ni,Co) 3 (Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.
To increase the lifetime of rocket combustion chambers, thermal barrier coatings (TBC) may be applied on the copper chamber wall. Since standard TBC systems used in gas turbines are not suitable for rocket-engine application and fail at the interface between the substrate and bond coat, a new bond-coat material has to be designed. This bond-coat material has to be chemically compatible to the copper substrate to improve the adhesion and needs a coefficient of thermal expansion close to that of copper to reduce thermal stresses. One approach to achieve this is to modify the standard NiCrAlY alloy used in gas turbines by adding copper. In this work, the influence of copper on the microstructure of NiCrAlY-alloys is investigated with thermodynamical calculations, optical microscopy, SEM, EDX and calorimetry. Adding copper leads to the formation of a significant amount of β-NiAl and α-Cr. Reducing the aluminum and chromium content leads furthermore to a two-phase fcc microstructure.
In this paper the development of a new y'/ Y'-alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800°C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650°C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the 5-phase, allowing for solvus temperatures in excess of 1100°C. Consequently, the stability of the y'-phase can be increased by further addition of aluminum. At the same time the Ti-content is reduced to prevent formation of the r-(Ni,Co)3(Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.
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