On November 12, the 15th China International Aviation and Aerospace Exhibition was grandly opened in Zhuhai, Guangdong. During the six-day event, a total of 1,022 companies from 47 countries and regions participated in the exhibition. It is worth mentioning that one of the highlights of this air show is the prominent display in the field of new materials. In the new materials and application exhibition area, a series of innovative materials such as stealth materials, titanium alloy materials, and carbon fiber composite materials have become the focus, bringing a new scientific and technological experience to the audience.
It is reported that among the aerospace structural materials in service, metal structural materials are still dominant, and metal structural materials are widely and important in the aerospace field, among which titanium alloys and high-temperature alloys are the main metal structural materials. The research and development of metal materials, including high-temperature alloys, super-strong steels, titanium alloys, etc., as well as metal 3D additive manufacturing technology, not only improves the performance of aerospace equipment, but also promotes the vigorous development of related industries.
Superalloy
The development trend of deformed superalloys for aero engines and gas turbine disc forgings in China: the metallurgical quality and dosage of GH4169 alloy used below 650 °C continue to improve, becoming a model of "one material for multiple purposes", supporting the mass production and application of third-generation aero engines and other equipment; The new generation of alloys such as GH4169D, GH4065A and GH4096 with a temperature bearing temperature of 700~750 °C have been successfully developed and applied in engineering, supporting the development of four generations of aero engines and commercial turbofan engines. Alloys such as GH4720Li and GH7438 have been used in batches in a variety of small and medium-sized engines; The development and application of marine gas turbines and rocket engines have led to the development of GH4698, GH4742, GH4202 and other grades. In order to meet the application needs of higher generation engines, alloys such as GH4151 and GH4975 with a temperature bearing capacity of more than 800 °C are being developed in the near future, forming a relatively complete age-strengthened deformed superalloy system with a service temperature between 600~900 °C.
Powder superalloys have been widely used in military and civilian advanced aero engine turbine discs. On the whole, the development trend of nickel-based powder superalloys has the characteristics of "three highs and one low": high strength, high working temperature, high microstructure stability and low fatigue crack propagation rate. European and American countries took the lead in successfully developing the first generation of 650 °C high-strength powder superalloys, such as René 95, etc.; The second-generation 750 °C damage-tolerant powder-superalloys, such as René 88DT, and the third-generation high-strength-damage-tolerant powder-superalloys, such as ME3, etc.
The fourth-generation powder superalloy is based on the third-generation, through composition adjustment and process optimization to obtain a higher operating temperature, so that it has the characteristics of high strength, high damage tolerance and high working temperature, such as ME501, etc. At present, China has developed the first generation of powder superalloys represented by FGH4095 and the second generation of powder superalloys represented by FGH4096, and the third and fourth generations are still being developed and explored.
In recent years, China's superalloy system has made remarkable progress in the field of development and application, mainly driven by demand and supplemented by technology. However, superalloys involve many disciplines, high component manufacturing requirements, and small fault tolerance, and their mature applications are based on a comprehensive and in-depth understanding of R&D and manufacturing systems and long-term accumulation, so they need to be continuously strengthened in the future.
Ultra-high strength steel
Ultra-high strength steel refers to high specific strength structural steel with a yield strength of more than 1380 MPa, which plays an increasingly important role in aerospace, national defense and military industry, and the main application scenarios in the aerospace field are aircraft landing gear, engine shafts, gear bearings, frames, beams, rocket engine shells, etc. Typical aircraft landing gear materials are mainly 300M and Aermet 100 steel, both of which have ultra-high strength of more than 1930 MPa. 300M is a low-alloy ultra-high-strength steel, which is widely used in the landing gear of passenger aircraft, large military transport aircraft and fighter aircraft; AerMet 100 steel is the best ultra-high-strength steel for proven applications, and has been used in the landing gear of military aircraft such as F22 and F18E/F because of its excellent resistance to stress corrosion cracking and fatigue resistance.
In addition, Fe-Ni maraging steels have superior strength and toughness due to the precipitation of nano-scale intermetallic compounds during the aging process, and their typical steel grades are 18Ni C250 and C300 steels, which are mostly used in engine spindles and rocket engine housings [46]. GE and Leep engine spindles are made of GE1014 and ML340 steel of 2100~2300 MPa, and GC-24 steel with a strength level of 2400 MPa has been developed in China. Aerospace bearing gear steel stands for high-strength carburized stainless steel CSS-42L, with a maximum service temperature of 430 °C.
The super heat-resistant carburizing steel CH2000 under research is a fourth-generation aviation bearing gear steel, with a surface hardness of 65~68HRC after carburizing and heat treatment, a core tensile strength of more than 2000 MPa, and a service temperature of up to 450 °C, which is suitable for gears, bearings and transmission shafts and other transmission components of high-power density transmission systems of new generation aero engines and helicopters.
The stress corrosion resistance of ultra-high strength steel is also the focus of research in various countries. Ques Tek has developed a new type of secondary hardening ultra-high strength stainless steel FerriumS53 through material genetic engineering, which has good fracture toughness and has been successfully applied to the landing gear components of the U.S. Air Force A-10 attack aircraft. China's independent research and development of 10Cr13Co13Mo5Ni3W1VE ultra-high strength stainless steel, has been successfully applied to the helicopter landing gear structure, the strength and toughness of the steel are better than FerriumS53 steel, for the highest strength level of ultra-high strength stainless steel, in the field of aerospace equipment manufacturing has a wide range of application prospects. Low-density high-strength steel is a new concept proposed in recent years, and its composition design is characterized by a high Al content while adding austenitizing elements, which gives it good plasticity, such as the most common Fe-Mn-Al-C quaternary system. In order to achieve the goal of reducing the weight and increasing the range of the aircraft and taking into account the economy, China has developed DT510 low-density steel, which has good strength and toughness while reducing the density of the material, compared with the traditional ultra-high strength steel 30CrMnSiNi2A, the density of DT510 is reduced by 13.4%, and the yield strength is increased by 19.3%.
Titanium alloy
Titanium alloy is the most valuable strategic metal material in the 21st century, and is one of the indispensable "spine" for the development of aviation and aerospace. In the process of titanium alloy cutting, problems such as serious tool wear, poor surface quality and low processing efficiency have become the bottlenecks restricting its development. It is of great significance to study the formation mechanism of tool wear and machined surface quality in the cutting process of titanium alloy, and to optimize and rationalize the cutting parameters of titanium alloy, which is of great significance to the development of aviation and aerospace fields. In the middle of the 20th century, military aircraft at home and abroad began to enter the supersonic age, and aero engines were transformed into jet engines, and steel and aluminum structures could no longer meet the requirements of the development of the times and were gradually eliminated. At the same time, titanium alloy has quickly entered the aerospace field with its excellent performance and has become one of the main structural materials in this field. It can be clearly seen that the proportion of titanium alloy in the fuselage of active aircraft is increasing rapidly. In advanced aero engine bodies, the proportion of titanium alloys usually remains above 20% and shows an increasing trend. However, the inherent difficult-to-machine properties of titanium alloy have become the bottleneck restricting its development due to serious tool wear, poor machining surface quality and high processing cost. In addition, as an upstream supply industry in the fields of aviation and military industry, additive manufacturing technology is increasingly recognized by aviation applications, and at the same time, a number of additive manufacturing companies appeared at the Zhuhai Air Show, including additive manufacturing materials, equipment and processing service companies.
The application of new processes such as additive manufacturing in the field of military materials continues to expand. With the increasing maturity of the cost control, large-scale production, product quality control, and technical level requirements of the additive manufacturing industry, its expansion in military applications has also entered a stage of rapid development. China's metal structural materials industry is on the rise, and there is an urgent need for variety innovation and technological progress.
