TC4(Ti-6A1-4V) titanium alloy is a typical alpha+beta dual-phase titanium alloy, which is the most widely used and mature titanium alloy at present. The alloy has the advantages of small degree, high specific strength, good thermal stability, good weldability, excellent comprehensive performance, and can be widely used as a load-bearing structural material in aerospace, Marine industry, automobile, electric power and other industries. Taking the aerospace industry as an example, TC4 titanium alloy can be used to manufacture the shell of the space rocket, the fan and blade of the aviation engine, the main bearing structural parts such as various beams, spacer frames, rails, landing gear beams of the aircraft structure, and various types of fasteners
The performance of the material is determined by the organization, and different types of organization determine different mechanical properties in order to be applied to different actual working environments. TC4 titanium alloy heat treatment process is very sensitive to organizational changes, through heat treatment, deformation and other processing methods can obtain different characteristics of the organization, such as the two-phase ratio, shape, distribution, etc., there are great differences. The common structure of TC4 titanium alloy mainly has the following four categories: equiaxial structure, net basket structure, duplex structure and homologous structure
The equiaxed structure is characterized by the distribution of more than 30% equiaxed alpha phase on the beta transition matrix. It is generally formed at 30~100 ° C below the beta transition temperature point, after sufficient recrystallization annealing and sufficient plastic deformation process. The lower the annealing temperature, the more full the plastic deformation, the smaller the equiaxial alpha grain and the higher the proportion. The equiaxial structure has good comprehensive properties and has been widely used at present. Its elongation, section shrinkage and plasticity are high. But the impact resistance, high temperature resistance, fracture toughness and creep strength are poor.
The morphology of the net basket structure is characterized by the distribution of interwoven lamellar alpha phases on the beta transition matrix, and the whole structure is like a net basket. It is generally heated or deformed in the bbeta phase region and formed when the deformation is terminated in the alpha+beta two-phase region. If the deformation is large in the two-phase region, the short sheet alpha phase spheroidizes to form an equiaxed structure. The basket structure has high lasting strength and good creep resistance, excellent thermal strength, and is generally used in the production of parts used at high temperatures for a long time. In addition, the fatigue crack propagation rate of this kind of structure is low, which is suitable for structural parts with high damage tolerance performance. However, the plasticity of the basket structure is poor, the thermal stability is low, and "beta brittleness" may appear. The avoiding method is to reduce the size of the original beta grain by shortening the heating time and temperature in the beta phase region
