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The jet engine is the most complex element of an aircraft and one of the most complex human-made products ever developed, housing thousands of individual components — and ultimately determining fuel efficiency for aircraft
All turbines operate on similar principles: A gas or other fluid turns a rotor, which can do useful work. In a jet engine, air is taken in and compressed, then fuel is added and combusted to heat the air, which then turns the rotor blades of a turbine. The hot exhaust is then expelled through a nozzle to create thrust. Since it was invented, the aviation version of the gas turbine (a common workhorse for the generation of electricity) has been continuously upgraded by legions of engineers. One of the most fruitful paths toward better performance has been finding ways to increase thermal efficiency—the amount of fuel that actually turns into the desired output and not waste heat—by raising the temperature at which the jet engine operates.
Gas turbine thermal efficiency increases with greater temperatures of gas flow exiting the combustor and entering the turbine. In modern, high-performance jet engines, the temperature of this gas can exceed 1,650 degrees Celsius (nonaviation gas turbines operate at 1,500 degrees or lower, whereas military jet engines can reach 2,000 degrees, which exceeds the boiling point of molten silver).
Jet engines also need to work in temperatures up to 1,500°C and under high-stress conditions. Creating turbine parts that can survive extreme heat has been a major engineering challenge. Meeting it has required fundamentally rethinking the material structure of the turbine blades, making metals do things that they do not normally do in nature.
Traditionally, certain materials have been used specifically for different parts of the jet engine as seen in the image below.
Since the 1950s, in high-temperature regions of the turbine, special blades and vanes are made from a combination of metals based on high-melting-point nickel. This material is called a “superalloy” because it retains strength and resists oxidation at extreme temperatures. They use materials such as ceramic matrix composites, high-temperature metals, and carbon-fibre composites.
However, considering that the melting point of current superalloys is around 1,850°C, the challenge becomes finding materials that will withstand hotter temperatures; and as such, the search for new materials has come to the fore. The advent of lean-burn engines, with temperature potentials as high as 2,100°C, has helped drive demand for these new materials. To achieve higher thrust, higher operating temperatures must be realized and for higher efficiency, engines must be made significantly lighter without loss of thrust. In either case, new families of materials need to be developed that have higher melting points and greater intrinsic strength.
Since fuel efficiency and performance increase with engine temperatures, new materials that can tolerate these temperatures must be tested before they are used in the engines, MTS stated. MTS Systems is working on the development and demonstration of new, advanced materials testing technologies, as part of a cooperative research and development agreement (CRADA) signed with the US Air Force (USAF). The testing of these materials will ensure safety, reliability and improved performance, according to the statement.
Ultrahigh Temperature Impervious Materials Advancing Turbine Efficiency (ULTIMATE) program
The U.S. Department of Energy today announced $16 million in funding for 17 projects as part of Phase 1 of the Advanced Research Projects Agency-Energy’s (ARPA-E) Ultrahigh Temperature Impervious Materials Advancing Turbine Efficiency (ULTIMATE) program. ULTIMATE teams will develop ultrahigh temperature materials for gas turbine use in the aviation and power generation industries.
ULTIMATE projects address two target temperature levels and seek to develop ultrahigh temperature materials for continuous operation at 1300 ºC (2372 ºF) in a stand-alone material test environment or at 1800 ºC (3272 ºF) with coatings and cooling. Teams will also develop new manufacturing processes that ensure turbine blades can not only operate at these ultra-high temperatures but can also withstand the extreme operating environments commonly found in natural gas turbines in both the aviation and power generation industries. The successful materials must be able to withstand not only the highest temperature in a turbine but also the extreme stresses of a turbine blade.
This program will concurrently fund the development of manufacturing processes for turbine components using these materials, enabling complex geometries that can be seamlessly integrated in the system design. Coatings including both environmental barrier coatings (EBC) and thermal barrier coatings (TBC) are also within the scope of this program. It is expected that the development of novel ultrahigh temperature materials in combination with compatible coatings and manufacturing technologies will enable the efficiency of gas turbines to be improved by up to 7%, which will result in significant reductions in wasted energy and carbon emissions. The motivation of this program is to improve the efficiency of gas turbines by increasing the temperature capability of the materials used in the most demanding environments such as the turbine blade.
“Natural gas turbines generate more than a third of the country’s electricity, supplying power to consumers across America,” said ARPA-E Director Lane Genatowski. “ULTIMATE teams will improve the efficiency of the generation sector by developing materials that increase producers’ efficiency and create positive economic benefits for industrial and public consumers nationwide.”
Phase 1 ULTIMATE teams will demonstrate proof of concept for alloy compositions, coatings, and manufacturing processes through modeling and laboratory scale tensile coupon testing of basic properties. At the conclusion of Phase 1, teams will be down-selected based on technical review to receive additional funding for development of selected alloy compositions and coatings, as well as the production of generic small-scale turbine blades to demonstrate manufacturability of designs. In ULTIMATE Phase 2, up to $14 million in additional funds will be available to teams.
ARPA-E’s ULTIMATE program supports the White House Office of Science and Technology Policy’s Industries of the Future initiative, supporting the development of key emerging technologies that will shape the nation’s economy and security for years to come.
Pennsylvania State University. Design and Manufacturing of Ultrahigh Temperature Refractory Alloys- $1,200,000.
Refractory metals are generally not considered good prospects for aerospace applications due to the fact that none of them satisfactorily meets the criterion of being oxidation resistant, and almost all of them, with the exception of chromium, are significantly denser than the existing Ni-based alloys. Combustion chambers are generally made up of superalloys with refractory metals such as tungsten, molybdenum, niobium, and tantalum.
Pennsylvania State University (PSU) will develop an integrated computational and experimental framework for the design and manufacturing of ULtrahigh TEmperature Refractory Alloys (ULTERA). Penn State will generate alloy property data through high-throughput computational and machine learning models; design ultrahigh temperature refractory alloys through a neural network inverse design approach (where one first articulates the needed functionality/property, and then looks for the materials that haves the property); manufacture the designed alloys utilizing field assisted sintering technology and/or additive manufacturing; and demonstrate the performance through systematic characterization in collaboration with industry.
The proposed platform with a sustainable data ecosystem could create fundamentally new approaches to understand and design a new generation of materials and provide pathways to improve existing materials to meet performance requirements.
GE Research. ULTIMATE Refractory Alloy Innovations for Superior Efficiency (RAISE) – $1,600,000.
GE Research has proposed transformational material solutions to potentially enable a gas turbine blade alloy-coating system capable of operating at a turbine inlet temperature of 1800 °C (3272 °F) for more than 30,000 hours. GE aims to develop a niobium (Nb)-based alloy that can operate at 1300 °C (2372 °F). The total proposed program effort includes development of a coating system consisting of a novel oxidation resistant bond coat compatible with the new Nb-based alloy and a thermal barrier coating for improved durability that can operate at 1700 °C (3092 °F) and a scalable manufacturing process for producing internally cooled gas turbine blades.
Application of the new technologies to existing combined cycle gas turbines in the U.S. could increase the thermal efficiency by approximately 7%.
Oak Ridge National Laboratory. Facility for Evaluating High Temperature Oxidation and Mechanical Properties – $1,500,000.
Oak Ridge National Laboratory (ORNL) will provide independent, accurate data on alloys and coatings developed by ULTIMATE teams. ORNL will supply technical performance target data, including room temperature and 1300°C (2372 °F) mechanical properties, post-exposure mechanical properties for coatings, and physical properties including thermal expansion and thermal conductivity. Additionally, ORNL will provide state-of-the-art characterization of as-received and post-test microstructure of alloys and coatings to assist in interpreting results.
Facilities include high temperature furnaces for 1700°C (3092 °F) oxidation exposures and frames for mechanical properties testing of creep (deformation) and tensile properties using small- or full- scale specimens. ORNL aims to coordinate with ULTIMATE teams to deliver data within 4 weeks of receipt of specimens for most of the target experiments.
Raytheon Technologies Research Center. Computationally Guided ODS Refractory HEAs via Additive Manufacturing – $800,000.
To achieve higher efficiency turbine operation, Raytheon Technologies Research Center will use additive manufacturing (AM) to produce test coupons (specimens) and potentially a representative turbine blade using a high entropy alloy (HEA) enhanced with oxide dispersion strengthening (ODS) particles.
HEAs, with multiple principal elements, offer a vast alloy design space and enhanced solid solution strengthening; a novel machine learning framework will be used to guide the HEA discovery process.
ODS alloys, which consist of a metal matrix with nano-scale oxide particles dispersed within it, are some of the best performing materials for high-temperature applications. Combining HEAs with ODS imparts high-temperature strength and creep (deformation) resistance to enable 1300 °C (2372 °F) operation that significantly exceeds the capability of current single crystal nickel superalloys. Deploying this class of alloys for 1300 °C turbine operation will allow airlines to save millions of gallons of fuel per year.
Raytheon Technologies Research Center. Environmental Protection Coating System for Refractory Metal Alloys (EPCS for RMAs) – $700,000.
The drive for higher fuel efficiency and higher core power of gas turbines used in electric power generation and aircraft propulsion requires higher peak operation temperatures in the hottest sections. Current state-of-the-art refractory metal alloys (RMAs), although highly resistant to heat and wear, tend to oxidize in the gas turbine environment. Raytheon Technologies Research Center aims to develop an environmental protection coating system (EPCS) for RMAs to radically improve long-term protection in the harsh gas turbine environment.
If successful, the integrated EPCS could profoundly improve coating service life and meet long-term environmental protection requirements for RMAs over a wide temperature range required in future fuel efficient gas turbine applications.
University of Maryland. New Environmental-Thermal Barrier Coatings for Ultrahigh Temperature Alloys – $600,000.
The University of Maryland will leverage a newly invented, ultrafast high-temperature sintering (UHS) method to perform fast exploration of new environmental-thermal barrier coatings (ETBCs) for 1300 °C (2372 °F)-capable refractory alloys for harsh turbine environments.
UHS enables ultrafast synthesis of high-melting oxide coatings, including multilayers, in less than a minute, enabling rapid evaluation of novel coating compositions. By using UHS with fast-fail tests and modeling and analytics tools, the team will be able to explore hundreds of compositions and coating architectures to design and optimize 1700 °C (3092 °F)-capable ETBCs with different layer sequences, thicknesses, porosity levels, and novel compositions.
University of Virginia. High Entropy Rare-earth Oxide (HERO) Coatings for Refractory Alloys- $600,000.
A turbine engine’s combustion environment can rapidly degrade high temperature alloys, which means they must be coated. This coating must be able to expand with the alloy so it adheres during temperature cycling, prevent combustion gases from permeating to the underlying alloy, and possess ultra-low thermal conductivity to protect the alloy from high surface temperatures.
The University of Virginia will develop a novel coating for high-temperature alloys that achieves these goals via a mixture of oxides of rare earth metals with different mass, ionic size, and charge. The coating will enable a significant increase in upper use temperature for turbine engine blades and increased engine efficiency. It will be manufactured using conventional air plasma spray or novel slurry-based processing to reduce cost and enable reparability.
University of Utah. Designing Novel Multicomponent Niobium Alloys for High Temperature:
Integrated Design, Rapid Processing & Validation Approach- $800,000. The University of Utah will use physical metallurgy principles and artificial intelligence to identify the chemistry of new niobium (Nb)-based refractory alloys to ensure they have excellent high-temperature properties without being brittle at low temperatures.
The computational materials models will be used to predict the proper processing conditions for the material chemistries. This two-step process can down-select the alloy compositions and manufacturing conditions from millions of possibilities, greatly reducing the time and cost for the search of new materials. The team will perform laboratory-scale experiments to fabricate sample alloys with the selected compositions and processing conditions. If successful, the project will identify the alloy compositions and processing conditions to potentially produce turbine blades that can operate at the temperatures significantly higher than the current state of the art.
Texas A&M Engineering Experiment Station. Batch-wise Improvement in Reduced Design Space using a Holistic Optimization Technique (BIRDSHOT) – $1,200,000.
Increasing the efficiency of power generation and air transportation can only be achieved by increasing the temperature at which generation/propulsion turbines operate. The emerging Refractory High Entropy Alloys (RHEAS) can enable much higher operating temperatures than the state-of-the-art. Identifying the alloys’ chemistry is difficult due to the vastness of the RHEA chemical space, however.
BIRDSHOT proposes an interdisciplinary framework combining physics-based modeling, machine learning, and artificial intelligence as well as high-throughput synthesis and characterization platforms to explore the RHEA space in a parallel fashion. BIRDSHOT aims to discover alloys that can potentially withstand the extreme environments in a gas turbine, retain compatibility with protective coatings, and are amenable to additive manufacturing, resulting in significant energy savings in power generation and transportation.
West Virginia University. High-Throughput Computational Guided Development of Refractory Complex Concentrated Alloys-based Composite- $700,000.
West Virginia University (WVU) will develop a new class of ultra-high temperature Refractory Complex Concentrated Alloys-based Composites (RCCC) for high temperature applications such as combustion turbines used in the aerospace and energy industries. The RCCC will consist of Refractory Complex Concentrated Alloys (RCCA) mixed with nanosized particles of Refractory High Entropy Carbides, to increase RCCA strength to withstand extreme conditions. The goal is to optimize the balance among strength, creep (deformation), density, and stability at 1300 °C (2372 °F), while maintaining ductility (malleability) once the alloy cools to room temperature. The research team will develop a specialty 3-D metal printing process to produce test coupons and potentially components such as turbine blades.
The Boeing Company. Ultra-High Performance Metallic Turbine Blades for Extreme Environments – $800,000.
Boeing Research & Technology aims to develop a comprehensive solution for ultra-high performance turbine blades and other extreme environment aerospace applications. The team will develop a series of novel refractory complex concentrated alloys (RCCA) and their processing parameters for both laser powder bed fusion additive manufacturing and advanced powder metallurgy manufacturing, as well as intermediate layer materials optimized for coating solutions.
This comprehensive solution will demonstrate a base alloy capability up to 1300 °C (2372 °F), and a coating capable of service in a turbine engine environment up to 1800 °C (3272 °F). The team will use advanced, high-throughput computational and experimental approaches to design and optimize the RCCAs to exploit the potential performance of such systems at significantly higher temperatures than current nickel- and cobalt- based superalloys.
National Energy Technology Laboratory. Rapid Design and Manufacturing of High-Performance Materials for Turbine Blades Applications above 1300 Celsius- $1,500,000.
The National Energy Technology Laboratory (NETL) will develop lightweight, cost-effective, precipitation- strengthened refractory high entropy alloys (RHEAs) for additive manufacturing. The alloys will comprise a ductile (malleable) high entropy solid solution matrix strengthened by fine precipitates of the high entropy carbides. NETL will use high throughput, multi-scale computer modeling, and machine learning (ML) to identify novel alloys within the large compositional space.
The team will integrate computational and experimental additive manufacturing (AM) research into the alloy design effort with the aim of producing sound articles with stable and desirable microstructures and providing feedback to the alloy design. At completion, the project will demonstrate a disruptive alloy and technology for potentially manufacturing turbine blades for service at temperatures greater than 1300 °C (2372 °F).
University of Wisconsin-Madison. Additive Manufacturing of Ultrahigh Temperature Refractory Metal Alloys- $650,000.
Current alloys used in gas turbines operate at about 90% of their melting temperature, which sets a limit on achieving higher temperatures. Refractory metal alloys (RMA) have the capability to enable continuous operation at 1300°C (2372 °F) and with compatible coatings along with cooling systems to allow for gas inlet temperatures to reach 1800°C (3272 °F). The high RMA melting temperatures present challenges for traditional manufacturing methods, however. The University of Wisconsin will use a novel additive manufacturing approach based upon a thermodynamically guided alloy selection, high-throughput materials synthesis and characterization using reactive synthesis of powders, and an innovative processing scheme for the fabrication of test coupons and potentially turbine components.
Oak Ridge National Laboratory. Development of Niobium-Based Alloys for Turbine Applications – $700,000.
Current nickel (Ni)-based alloys used in turbine blade applications are operating at 1100 °C (2012 °F), which is approximately 90% of their melting temperatures. Refractory alloys, such as niobium (Nb) alloys, can withstand higher temperatures. Oak Ridge National Laboratory (ORNL) will use computational modeling tools and advanced characterization to develop two classes of Nb alloys for use in a tri-layered turbine blade that can continuously operate at 1300 °C (2372 °F) with coatings. This capability will enable gas turbine inlets of 1800 °C (3272 °F) or higher.
Pacific Northwest National Laboratory. Selective Thermal Emission Coatings for Improved Turbine Performance – $600,000.
Pacific Northwest National Laboratory aims to develop a new type of thermal barrier coating that performs dual functions. The coating will act as a barrier to conventional heat transfer and have ability to alter the wavelength of light radiated from the hot turbine blade surface. This normally wasted energy will be absorbed in the turbine exhaust where it can produce additional electrical power or thrust.
Simulations show this new coating could increase turbine output by as much 6%. The project team will design, synthesize, and measure the optical and thermal properties of candidate coatings for operation at up to 1800 °C (3272 °F). Coatings passing performance tests will be implemented on gas turbine blades that will be tested in a mini-turbine to measure coating impact on turbine output.
Massachusetts Institute of Technology. Additive Manufacturing of Oxidation-Resistant Gradient Refractory Composites – $600,000.
Massachusetts Institute of Technology will develop a new additive manufacturing (AM) process, capable of producing refractory composite materials for use in high-temperature, oxidation-resistant turbine blades and other demanding energy-conversion applications. The AM process will incorporate hardware and software to establish uniform, high-quality refractory materials that are traditionally prone to micro-cracking and oxidation during AM, and thereby establish the required mechanical properties and oxidation resistance of a target alloy.
In synergy with materials development and evaluation, the team will build two generations of a new AM system, ultimately enabling digital production of representative turbine blade geometries with low surface roughness and high-precision, complex internal cooling channels.
QuesTek Innovations LLC. Concurrent Design of a Multimaterial Niobium Alloy System for Next-generation Turbine Applications- $1,200,000.
QuesTek Innovations will apply computational materials design, additive manufacturing, coating technology, and turbine design/manufacturing to develop a comprehensive solution for a next-generation turbine blade alloy and coating system capable of sustained operation at 1300 °C (2372 °F). QuesTek will design a niobium (Nb)-based multi-material alloy system consisting of a ductile, precipitation-strengthened, creep (deformation)- resistant alloy for the turbine “core” combined with an oxidation-resistant, bond coat-compatible Nb alloy for the “case.”
The proposed multi-material Nb alloy and coating system will achieve a combination of properties suitable for a variety of gas or industrial turbine components such as blade, vane, and panel structures. Concurrent design of both alloy and component will enable next-generation technologies within an accelerated timeline.
References and Resources also include:
https://www.prescouter.com/2020/06/jet-engines-high-temperature-materials/
