Development status of high strength and high elasticity titanium alloy

The elastic deformation ability of metal materials is affected by the yield strength and elastic modulus, and the elastic limit of the tensile line (ε0.2) is generally less than 1%. The strength of traditional titanium alloy is in the range of 400~1500 MPa according to the alloy grade, and the elastic modulus is in the range of 50~120 GPa, which is much lower than that of steel (about 210 GPa), and the elastic deformation capacity is about twice that of steel. Titanium alloy is widely used in aerospace field because of its high strength and low modulus of elasticity, which has excellent elastic deformation ability.

In the 1950s, the United States first used titanium bolts made by Ti-6AL-4V on B-52 bombers, which opened the application of titanium fasteners in the aerospace field. With the continuous lightweight requirements of aerospace and weapons equipment, the application of lightweight, high strength and high elasticity titanium alloy in fasteners has gradually replaced the traditional 30CrMosia steel, improving the safety and reliability of equipment. At present, the commonly used α+β and β-type titanium alloys, 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), the tensile strength of the basic 1000 MPa grade. Since the 1970s, McDonnell Douglas has been using Ti-13V-11Cr-3AL to make civil aircraft springs, replacing spring steel and reducing weight by 70%.Later, Lockheed, Boeing, and Airbus began using β-titanium for spring components such as landing gear up-and-down locks, hydraulic return, and aircraft control. The typical alloys are Ti-15V-3Cr-3Al-3Sn and Ti-3Al-8V-6Cr-4Mo-4Zr (β-C) with an elastic modulus of about 104 GPa. The tensile strength is 1300~1450 MPa.

Typical brands used in China are TB2, TB3 and TB5.At present, α+β and β-type titanium alloys used for springs and fasteners are generally made of α+β two-phase structure to obtain high strength. At the same time, the elastic modulus (90~120 GPa) is also high, which leads to the low elastic properties. Therefore, it is difficult to meet the requirements of advanced aircraft for high strength and high elasticity materials. As a special rivet material, β-type Ti-45Nb alloy has been widely used in aerospace products at home and abroad. The alloy has the advantages of low elastic modulus, good plasticity and good formability in cold working, but the strength, especially the yield strength, is low, and the match between strength and elastic property 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, such as Ti-29Nb-13Ta-4.6Zr and Ti-35Nb-5Ta-7Zr, have been developed to obtain better elastic properties. However, the titanium alloy was developed for the medical field. Titanium alloy has low strength and is difficult to meet the requirements of high strength and high elasticity of titanium alloy used for aviation fasteners and springs. In 2003, Toyota Institute of Central Research, Japan, developed a multi-functional titanium alloy (rubber metal) with excellent comprehensive performance, typical composition is Ti-23Nb-0.7Ta-2Zr-1.22O (atomic fraction %), the alloy after 90% cold rolling deformation strength can reach 1200 MPa, the modulus of elasticity is 55 GPa, The elastic limit can be up to about 2.5%, showing excellent high strength and high elastic match, the 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, Chinese Academy of Sciences, also exhibits excellent elastic properties, with elastic modulus as low as 42 GPa and elastic strain as high as 3.3%.After solution and aging treatment, it also has excellent matching of high strength and high elasticity. Rubber metal and TI-2448 are the typical representatives of advanced high strength and high elasticity titanium alloy, which indicates that titanium alloy can achieve the match of high strength and high elasticity, and its excellent performance depends on the ingenious composition design and appropriate preparation process.