On June 20, 2016, the team of Professor Guang Chen from Nanjing University of Science and Technology, funded by the National 973 Program, after long-term research, achieved a leapfrog breakthrough in the new aerospace material titanium aluminum alloy. On June 20, the relevant results were published online in Natural Materials. Its room temperature tensile plasticity, yield strength, high-temperature creep resistance, temperature-bearing ability and other key performance indicators are internationally leading, 1-2 orders of magnitude more than similar materials in the United States.
In 2007, the Boeing 787 aircraft was successfully tested. This new aircraft can save 20% of fuel, reduce NOx emissions by 80%, and significantly reduce noise, which has attracted global attention.
This aircraft engine was developed by General Electric (GE) in the United States, using Ti-48Al-2Cr-2Nb (hereinafter referred to as 4822) alloy instead of nickel-based superalloy to produce the last two stages of low-pressure turbine blades.
This is the first time that titanium-aluminum alloy has been applied to aero engines.
The 4822 alloy used by GE is also not perfect. Its room temperature tensile ductility is less than 2%. Although it is enough to disregard other intermetallic compounds, it is still too brittle compared to nickel-based alloys. Therefore, GE used it on the two end blades with the lowest ambient temperature and the lowest risk factor, so that even if it breaks, it will not cause the entire aircraft to lose control.
Americans do so because the density of titanium aluminum alloy is only half of that of nickel-based alloys. On aircraft engines with grams as the unit of weight reduction, GE reduced the weight of a single engine by about 200 pounds, which became a sensational development in the aviation and materials field at that time.
Therefore, titanium aluminum alloy is currently recognized as the best new lightweight structural material to replace nickel-based superalloys.
The research results of Professor Chen Guang’s team have achieved three major breakthroughs in material properties:
First, the room temperature tensile plasticity and yield strength are greatly improved, reaching 6.9% and 708MPa, respectively, and the tensile strength is as high as 978MPa, achieving an excellent combination of high strength and high plasticity. The second is excellent creep resistance. The third is to greatly improve the temperature-bearing capacity.
Aeroengines are known as the heart of aircraft, and are restricted by insufficient basic research capabilities. At present, my country's civil aviation engines basically rely on imports. Although military fighter engines have made some progress, there is still a gap between key performance indicators and developed countries. Among them, the turbine blade is the most critical core component in an aero engine, and its temperature-bearing capacity directly determines the performance of the engine, especially the thrust-to-weight ratio. Although the traditional nickel-based alloy has good performance in all aspects, its biggest disadvantage is that it is too heavy, which directly leads to the failure to improve the energy efficiency ratio of the engine. Therefore, scientists from various countries have never stopped their efforts to find suitable materials for manufacturing aero engines.
"One generation of materials, one generation of aero-engines." said Kang Jianxiong, deputy director designer of the Turbine Design Department of China Institute of Aeronautical Power Machinery. It is also expected to be used in components such as turbine disks and high-pressure compression turbines.
There is still a long way to go for a new type of material from the laboratory to the installation on the plane. According to Chen Guang's estimation, there are still 5-10 years to realize the application of PST titanium aluminum alloy.