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Optimizing the toughness of titanium alloys by combining hardness and microstructure

The key to optimizing the toughness of titanium alloys by combining hardness and microstructure is to finely control the phase composition, proportion and morphology of the alloy to achieve a synergistic improvement in strength and toughness. Specific methods and principles include:

1. Regulating the α+β two-phase microstructure
The structural titanium alloy is mainly composed of the α phase of the hcp structure and the β phase of the bcc structure. By finely controlling the composition, proportion and morphology of the two phases, the coordinated deformation ability between the two phases can be improved, the interfacial stress concentration can be reduced, and the overall toughness can be improved. For example, optimizing the matching of the elastic modulus of the α phase and the β phase and the critical shear stress of dislocation slip can help delay the formation of microcracks and microvoids and enhance toughness.

2. Inhibiting the precipitation of brittle phases
Through alloy element design and heat treatment control, the excessive precipitation of brittle ω phase and Ti₃Al phase can be suppressed to avoid these brittle phases from reducing the plasticity and toughness of the alloy.

3. Induced deformation twinning and phase transformation toughening
Regulating the composition of the two-phase micro-region can induce deformation twinning of the α phase and deformation-induced phase transformation of the β phase, resulting in twinning plasticization and toughening effects, which significantly improves the fracture toughness of the material.

4. Multi-scale microstructure design
Preparing multi-scale and multi-level microstructures is an important means to achieve plasticization and toughness of titanium alloys. Through heat treatment and plastic deformation, fine and uniform α phase precipitation and optimized β matrix are formed, which improves hardness while ensuring toughness.

5. Combination of plastic deformation and heat treatment process
Moderate plastic deformation in the α-β phase region (such as achieving at least 25% area reduction), followed by controlled single-step or multi-step heat treatment, can significantly improve the strength and toughness combination of titanium alloys. This method simplifies the traditional complex heat treatment process and optimizes the balance between hardness and toughness through microstructural changes induced by plastic deformation.

6. Basket-shaped α-phase microstructure
The formation of a uniform basket-shaped α-phase lath structure helps to achieve a combination of high strength and high toughness. This structure is obtained by controlling the cooling rate and heat treatment process, which can effectively hinder crack propagation and improve fracture toughness.

Summary:
By finely controlling the microstructure of titanium alloys (especially the ratio, morphology and composition of the α+β phases), rationally designing alloy elements and optimizing the heat treatment process, the fracture toughness and plasticity of the material can be significantly enhanced while improving the hardness (strength). The increase in hardness reflects the strengthening effect of the material, while the optimization of the microstructure ensures the toughness performance of the material. The combination of the two is the core strategy for the design of high-strength and tough titanium alloys.