The current development status of high-strength and high-elastic titanium alloys

The elastic deformation ability of metallic materials is influenced by the yield strength and elastic modulus. The linear elastic limit (ε0.2) of tensile tests is mostly lower than 1%. The strength of traditional titanium alloys varies from 400 to 1500 MPa depending on the alloy designation, and the elastic modulus ranges from 50 to 120 GPa, which is much lower than that of steel (about 210 GPa). The elastic deformation ability of titanium alloys is approximately twice that of steel. The high strength and low elastic modulus of titanium alloys give them excellent elastic deformation ability, and they are widely used in aerospace fields as integrated structural-functional materials.

In the 1950s, the United States began to use titanium alloy bolts made of Ti-6Al-4V on B-52 bombers, thus initiating the application of titanium alloy fasteners in the aerospace field. With the continuous light weighting requirements in aerospace and weaponry, lightweight, high-strength, and highly elastic titanium alloys gradually partially replaced the traditional 30CrMoSiA steel in the application of fasteners, improving the safety and reliability of equipment usage. Currently, the tensile strength of the commonly used α+β and β types of titanium alloys is basically at the 1000 MPa level, such as Ti-6Al-4V, Ti-3Al-5Mo-4.5V, Ti-5Mo-5V-8Cr-3Al, and Ti-15Mo-3Al-2.7Nb-0.3Si (β 21S), etc.

Since the 1970s, McDonnell Douglas has been using Ti-13V-11Cr-3Al to manufacture springs for civilian aircraft, replacing spring steel to achieve a weight reduction of 70%. Subsequently, Lockheed, Boeing, and Airbus, among others, began using β titanium alloy materials to manufacture spring components such as the upper and lower locks of landing gears, hydraulic return paths, and aircraft controls. Representative alloys include Ti-15V-3Cr-3Al-3Sn and Ti-3Al-8V-6Cr-4Mo-4Zr (β-C), with an elastic modulus of approximately 104 GPa and a tensile strength of 1300-1450 MPa.

The typical grades used domestically include TB2, TB3 and TB5, etc. Currently, the α+β and β types of titanium alloys used for springs and fasteners generally adopt the α+β two-phase structure to achieve high strength, and their elastic modulus (90-120 GPa) is also relatively high, resulting in poor elastic performance and difficulty in meeting the requirements of aircraft for high-strength and high-elastic materials. The β-type Ti-45Nb alloy, as a special material for rivets, has been applied in domestic and international aerospace products. This alloy has the advantages of low elastic modulus, good plasticity and cold working formability, but its strength, especially the yield strength, is low, and the matching between strength and elastic performance is poor.

Since the 1990s, in order to reduce the elastic modulus of medical titanium alloys, a series of low elastic modulus metastable β-type titanium alloys have been developed, such as Ti-29Nb-13Ta-4.6Zr and Ti-35Nb-5Ta-7Zr, etc. These alloys have achieved better elastic properties, but they are developed for the medical field and have low strength, making it difficult to meet the usage requirements for high strength and high elasticity of titanium alloys used in aviation fasteners and springs. In 2003, the Toyota Central Research Institute in Japan developed a multifunctional titanium alloy (rubber metal) with excellent comprehensive performance. The typical composition is Ti-23Nb-0.7Ta-2Zr-1.2O (atomic fraction %). After 90% cold rolling deformation, the strength of this alloy can reach 1200 MPa, the elastic modulus is 55 GPa, and the elastic limit is approximately 2.5%, showing excellent high strength and high elasticity matching, and this alloy has constant elasticity over a wide temperature range.

The metastable β-type alloy Ti-24Nb-4Zr-8Sn (Ti-2448), developed by the Institute of Metal Materials of the Chinese Academy of Sciences, also exhibits excellent elastic properties, with an elastic modulus as low as 42 GPa and an elastic strain as high as 3.3%. After solution treatment, it also possesses excellent high strength and high elastic matching. Rubber metal and Ti-2448 are typical representatives of high-strength and high-elastic titanium alloys, indicating that titanium alloys can achieve a high-strength and high-elastic matching. Their excellent performance relies on ingenious component design and appropriate preparation processes.