Supply Risk Considerations for the Elements in Nickel-Based Superalloys

Abstract

Nickel-based superalloys contain various elements which are added in order to make the alloys more resistant to thermal and mechanical stress and to the adverse operating environments in jet engines. In particular, higher combustion temperatures in the gas turbine are important, since they result in higher fuel efficiency and thus in lower CO2 emissions. In this paper, a semi-quantitative assessment scheme is used to evaluate the relative supply risks associated with elements contained in various Ni-based superalloys: aluminium, titanium, chromium, iron, cobalt, niobium, molybdenum, ruthenium, tantalum, tungsten, and rhenium. Twelve indicators on the elemental level and four aggregation methods are applied in order to obtain the supply risk at the alloy level. The supply risks for the elements rhenium, molybdenum and cobalt are found to be the highest. For three of the aggregation schemes, the spread in supply risk values for the different alloy types (as characterized by chemical composition and the endurance temperature) is generally narrow. The fourth, namely the cost-share’ aggregation scheme, gives rise to a broader distribution of supply risk values. This is mainly due to the introduction of rhenium as a component starting with second-generation single crystal alloys. The resulting higher supply risk appears, however, to be acceptable for jet engine applications due to the higher temperatures these alloys can endure.

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“…Recently, Helbig et al evaluated the supply risks associated with elements contained in average Ni-based superalloys (Figure 8). On the basis of twelve indicators in four supply risk categories, rhenium, molybdenum, and cobalt were found to have the highest supply risk scores, while titanium and aluminum the lowest [26]. With the increasing temperature reached in modern advanced aeroengines, materials with still higher temperature resistance are requested.…”

“…In 2019, Airbus forecasted an annual growth of 4.3%, requiring about 39,200 new passengers and dedicated freighter aircrafts over the next 20 years. Despite passenger travel activity decreasing sharply in 2020 due to the COVID-19 pandemic, a long-term recovery and a return to rapid growth in the aviation industry are expected [ 26 ]. Therefore, there is a growing need for new commercial airplanes with improved fuel efficiency and reduced pollution emissions [ 27 ].…”

“…For instance, General Electric (GE) developed a low-Re superalloy René N515 with considerably reduced rhenium content (1.2 wt.% Re) and with comparable mechanical properties to the second generation René N5 (3 wt.% Re). In fact, GE recently assessed the critical materials used in its manufacturing and commercial operations, and responded to shortages of rhenium by minimizing the amount of critical metals in superalloys, giving an example of successful strategies for combating raw material criticality [ 5 , 26 , 55 ].…”

“…This alloy has both high-temperature creep strength and improved oxidation resistance and is able to achieve 1000 h of creep life at 137 MPa and 1120 °C [ 56 ]. TMS-238 alloy has 60% of its raw material costs determined by rhenium and 30% by ruthenium, for a total cost of about 2400 USD per liter [ 26 ]. Up to now, sixth generation superalloys of the TMS series have been developed by finely tuning the alloying elements in order to enhance the oxidation-resistance at high temperature and improve the creep strength.…”

“… Supply risk score of elements in Ni-based alloys and the raw material price in a semi-logarithmic plot. Reprinted from [ 26 ] under an open access CC BY 4.0 license. …”