What Alloy Materials Are Needed for Aerospace Engines？

The development level of aerospace engines is a concentrated reflection of a country's comprehensive national strength, industrial foundation and scientific and technological level. Its research and development concentrates the most advanced technologies and industrial achievements of modern industry. This article will reveal to you the materials used in aerospace engines.

1. Aluminum alloy
Aluminum alloy has outstanding advantages such as high specific modulus and specific strength, good corrosion resistance, good processing performance and low cost. Therefore, it is considered to be the most important in the aerospace industry.
Main application locations: engine compartment, cabin structure, load-bearing wall panels, beams, instrument installation frames, fuel tanks, etc.

2. Titanium alloy
Compared with metal materials such as aluminum, magnesium, and steel, titanium alloy has the advantages of high specific strength, good corrosion resistance, good fatigue resistance, small thermal conductivity and linear expansion coefficient, etc. It can be used for a long time below 350~450℃, and can be used at low temperatures to -196℃.
Main application locations: compressor blades, casings, engine compartments and heat insulation panels of aircraft engines, etc.

3. Ultra-high strength steel
Ultra-high strength steel has high tensile strength and sufficient toughness, and has good weldability and formability.
Main application locations: aerospace engine housing, engine nozzle, bearings and transmission gears.
4. Magnesium alloy
Magnesium alloy is the lightest metal structural material, with low density, high specific strength, strong seismic resistance, and can withstand large impact loads.
Main application locations: aerospace engine casing, gearbox, etc.
Composite materials
The rapid development of aerospace engines, especially the increasingly stringent temperature and weight requirements, can no longer meet the gradually improved traditional materials, and instead call for materials science to open up a new system, that is, composite materials. According to the characteristics of each composite material, it can be used in different engine parts.

1. Metal-based composite materials
Metal-based composite materials mainly refer to composite materials with light metals such as Al and Mg as the matrix. In aviation and aerospace, it is mainly used to replace light but toxic beryllium. This type of material has excellent lateral performance, low consumption and excellent processability. It has become the most commercially attractive material in many application fields and has been commercialized abroad.
Main application location: suitable for use as the medium temperature section components of the engine.
With the rapid development of science and technology, some cutting-edge science and technology have made rapid progress, so higher requirements have been put forward for material performance. Traditional single materials are far from meeting the actual production needs. It is in such a big environment that composite materials came into being.
Take the application of composite materials in aircraft engines as an example. Although traditional aircraft engine materials (nickel alloys and titanium alloys) can still be further developed, their development space is not large, and it is difficult to meet the more stringent temperature and weight requirements of future aircraft engines. Nowadays, the performance of aircraft engines is constantly improving, and the weight has been greatly reduced compared with the past. While relying on novel structures such as integral blades, integral blade rings, hollow blades and counter-rotating turbines, more attention will be paid to advanced materials with high specific strength, low density, high stiffness and strong high temperature resistance. Now, resin-based composites, metal-based composites, ceramic-based composites and C/C composites have become candidate materials for aircraft engine fans and compressors because of their excellent low-temperature performance.

Advanced composite materials used in aircraft engines

Culvert casing
Compared with conventional titanium alloy fan culvert casing, the culvert casing made of resin-based composite materials can reduce the weight of the engine and the development cost of the engine while ensuring that it can perform all functions and withstand the static and flight loads of the entire engine.
GE's F404 engine was first improved from a titanium alloy culvert casing to a PMR15 composite culvert casing, achieving a 30% weight reduction and a 30% cost reduction. Later, GE further applied this technology to engines such as the F414 thrust-enhancing engine and the GenX engine.
The F191 and F135 engines of Pratt & Whitney in the United States and the M88 engine of Snecma in France all use culvert casings made of resin-based composite materials. The weight reduction and cost reduction effects are very obvious.

Stator blades
Compared with titanium alloy stator blades, resin-based composite stator blades can reduce weight by 50% and reduce costs by more than 50%. At the same time, by optimizing the fiber orientation, the natural frequency of the composite stator blades can be modified to increase the allowable mechanical and aerodynamic design space.
Pratt & Whitney's PW4084 and PW4168 engine fan stator blades use PR500 epoxy resin-based composite materials. Among them, the PW4084 engine with a diameter of 3.04 meters has a 39% reduction in weight and a 38% reduction in cost. Germany's MTU company uses PMC composite materials in the inlet guide vanes and first-stage or second-stage adjustable stator blades of the high-speed low-pressure compressor of the PW8000 engine. The ability of these blades to resist external damage, vibration resistance, corrosion resistance and structural integrity has been verified.

Rotor blades
The low density and high strength characteristics of composite materials can not only reduce weight, but also enable rotor blades to have 3D aerodynamic design shapes, such as swept blades and bow blades. In addition to reducing manufacturing costs, composite rotor blades also have non-destructive characteristics shown in shedding accidents, thereby reducing containment requirements.
The use of composite materials for fan blades can not only significantly reduce the weight of the blades themselves, but also reduce the weight of their containment system, disk and the entire rotor system. It has the characteristics of low cost, good vibration resistance and strong damage resistance. At present, GE's GenX and GE90-115B engines use high-flow curved composite fan blades and organic-based fan casings, and plans to further study composite hollow blade high-pressure ratio fans.

Metal-based composite materials
Compared with resin-based composite materials, metal-based composite materials have good toughness, do not absorb moisture, and can withstand relatively high temperatures. The reinforcing fibers of metal-based composite materials include metal fibers, such as stainless steel, tungsten, benzene, nickel, nickel-aluminum intermetallic compounds, etc.; ceramic fibers, such as alumina, silicon oxide, carbon, boron, silicon carbide, and titanium boride.

The matrix materials of metal-based composite materials include aluminum, aluminum alloys, magnesium, titanium and titanium alloys, heat-resistant alloys, and cobalt alloys. Among them, composite materials based on aluminum-carbon alloys, titanium and iron alloys are currently the main choices. For example, composite materials based on titanium alloys reinforced with silicon carbide fibers can be used to manufacture compressor blades. Carbon fiber or alumina fiber reinforced magnesium or magnesium alloy matrix composites can be used to manufacture turbofan blades. Another example is nickel-chromium-aluminum-iridium fiber reinforced nickel-based alloy matrix composites can be used to manufacture sealing elements for turbines and compressors.

GE has studied titanium-based composite low-pressure shafts for the joint technology verification engine program. The weight is 30% lighter than inco alloys, the rigidity is 40% higher than titanium alloys, and the life and durability are improved. If the F110 engine uses this composite shaft, the weight can be reduced by 68kg. In the near future, metal composites will replace nickel and titanium alloys and become the main materials for future aircraft engines.

New high-strength and tough titanium alloys/titanium-aluminum alloys/deformed high-temperature alloys and composite materials
Titanium alloys and titanium-aluminum (TiAl) alloys continue to develop with the demand for lightweight engines. The current maximum operating temperature of titanium alloys is 600-650℃, and the operating temperature range of TiAl alloys is 650-950℃, but its outstanding room temperature brittleness and notch sensitivity make it only a partial replacement for high-temperature alloys or single crystal alloys. In addition, as the operating temperature of each section of the engine increases, it is necessary to develop new deformable high-temperature alloys that are more heat-resistant and tougher.
my country has independently developed high-temperature titanium alloys since the 1980s. At present, it has mastered key technologies such as alloy composition, organization, performance matching control and optimization. The level of research and application has basically achieved synchronization with the international advanced level, but it is necessary to further improve the uniformity of organizational performance and tap the potential of alloys. For TiAl alloys, key breakthroughs have been made in key technologies such as material design, preparation process, organizational optimization and control, and plastic toughness improvement, and a number of representative alloys have been developed, but it is still necessary to deepen research on technologies such as high-strength and toughness organizational matching and low-plastic toughness material application design to expand their applications. With the advancement of alloy design methods and the development of casting-forging equipment and processes, a variety of new deformable high-temperature alloys have been successfully applied, but with the increase in the degree of alloying, the difficulty of alloy casting and hot addition processes has greatly increased. It is necessary to break through technical bottlenecks such as remelting and refining of large-size ingots and uniform deformation, achieve uniform and stable organizational performance, and achieve a comprehensive balance of performance, efficiency and cost, accelerate research and development and application, and lay the foundation for the independent research and development of higher-performance deformable high-temperature alloys in the future.
At present, the application of the integral blade disk structure in the cold-end rotor has reached the design limit, while the integral blade ring integrates advanced structure and materials, has excellent comprehensive performance and can achieve lightweight, and is the iconic choice for the lightweight rotor of the next generation engine. The application trend of SiC fiber reinforced titanium-based (Ti-MMC), TiAl-based (TiAl-MMC) and nickel-based composite materials (Ni-MMC) is rapidly increasing. MTU and Rolls-Royce have produced Ti-MMC integral blade rings (as shown in Figure 1), turbine shafts and other test pieces, and have conducted assessments, with significant lightweight effects. It is predicted that Ti-MMC will account for about 30% of the materials used in future engines, and TiAl-MMC will account for about 15%.

Since the 1990s, my country has started the research and development of Ti-MMC and its components. So far, it has successively made breakthroughs in key technologies such as high-performance monofilament SiC fiber mass production, high-quality pioneer wire preparation, and component forming, and opened up the integrated manufacturing technology route of Ti-MMC integral blade rings. However, it is still necessary to strengthen the research on technologies such as enhanced ring core shape control and residual stress regulation to give full play to the advantages of Ti-MMC.

New single crystal alloys and powder alloys
As the temperature before the turbine increases, the material of the turbine blade has developed from deformed and cast high-temperature alloys to oriented and single crystal high-temperature alloys, and the material of the turbine disk has developed from alloy steel and deformed high-temperature alloys to powder high-temperature alloys. In the past fifty or sixty years, the temperature before the turbine has increased by about 600K, and the materials and casting process have contributed 30% to 40%. Since Pratt & Whitney invented the world's first single crystal alloy PW1480, the industry has successfully developed multiple generations of nickel-based and nickel-aluminum (Ni3Al) single crystal alloys. China is one of the countries in the world that studied single crystal alloys earlier, and many grades have been gradually applied. However, with the development of engines, the current single crystal alloys are limited by temperature resistance and casting processability, and their application has reached the limit. It is urgent to develop new single crystal alloys with higher initial melting temperature, better microstructure and performance, good casting and welding processability, and acceptable cost.
Since the United States took the lead in developing powder high-temperature alloys and successfully applied them on turbine disks in the early 1960s, powder alloy turbine disks have accumulated tens of millions of hours of safe operation on multiple engines, and powder alloys have become the preferred material for turbine disks of advanced aircraft engines. The industry has developed high-generation powder alloys with higher service temperatures and better comprehensive performance, and has developed dual-performance/dual alloy and dual-spoke turbine discs according to the performance emphasis of different parts of the turbine disc. my country has successfully developed the first and second generation powder alloys, and is currently developing the third and fourth generation powder alloys. However, with the development of engines, in-depth research is still needed in high-quality powders, dual-performance/dual alloy/dual-spoke turbine disc preparation and low-cost processes.

Lightweight, high-strength, high-temperature resistant strategic and revolutionary advanced materials and processes are the iconic choice for future advanced aero engines. We should further focus on basic bottlenecks, engineering applications, resource investment, and dual-chain integrity, strengthen demand traction, strengthen industry overall management, strengthen system layout, strengthen collaborative integration, and strengthen centralized investment, so as to embark on a path of independence, self-reliance, and self-improvement in engine materials and processes with Chinese characteristics.