Titanium alloys are widely used in high-tech fields such as aerospace, biomedicine, and automotive manufacturing due to their excellent specific strength, good corrosion resistance, and high thermal stability. In the preparation and processing of titanium alloys, grain size is one of the key factors affecting their mechanical properties. Generally, fine grains can significantly improve the strength and toughness of the material, while coarse grains can lead to material embrittlement. Therefore, how to effectively control the grain size of titanium alloys has become an important research topic in the field of materials science.



1. Alloy Composition Design



The chemical composition of titanium alloys has an important impact on the grain size. By reasonably designing the types and contents of alloy elements, it is possible to effectively control the grain growth behavior. For example, in α+β type titanium alloys (such as TC4), adding appropriate amounts of β-stabilizing elements (such as Mo, V, Cr) can lower the phase transition temperature, expand the two-phase region, and thus make it easier to achieve grain refinement during heat processing. In addition, adding trace grain refinement agents (such as Zr, Sn) also helps to suppress grain growth.



2. Control of Heat Processing Technologies



Heat processing is one of the important means to control the grain size of titanium alloys. The deformation temperature, deformation rate, and deformation amount during plastic processing processes such as forging, rolling, and extrusion will significantly affect the final grain structure. Generally, high-temperature deformation in the β-phase area is beneficial for obtaining uniform coarse grain structures, while medium-temperature processing in the α+β two-phase area is more conducive to grain refinement. In addition, controlling the final forging temperature and the deformation amount of passes is helpful to achieve dynamic recrystallization or static recrystallization, thereby refining the grains.



3. Optimization of Heat Treatment Systems



Heat treatment is an important process means for regulating the microstructure and grain size of titanium alloys. Common heat treatment methods include annealing, solution treatment, and aging treatment, etc. For example, double annealing treatment of TC4 titanium alloy can promote grain refinement and improve the uniformity of the microstructure. Selecting appropriate annealing temperature and holding time can achieve microstructure optimization without causing excessive grain growth.



4. Application of Advanced Processing Technologies



In recent years, with the development of material processing technology, some new processes have also been applied to the control of titanium alloy grain size. For example, equal channel angular pressing (ECAP), high-pressure torsion (HPT), and laser additive manufacturing technology, etc., can achieve ultra-fine grain even nanocrystalline structures through severe plastic deformation or rapid cooling, thereby significantly improving the comprehensive performance of titanium alloys.



In summary, the control of titanium alloy grain size is a systematic project involving material composition design, optimization of processing technology, and adjustment of heat treatment systems. Through multi-method coordinated control, it is possible to effectively obtain titanium alloy materials with ideal grain structures to meet the high performance requirements of different application fields. In the future, with the continuous development of advanced manufacturing technology, the precise control of titanium alloy grain size will reach a higher level.