Welding Mechanism and Physicochemical Properties of Titanium Tubes

The nearby area has no protective effect, and the titanium tubes near and at the weld still have a strong ability to absorb nitrogen and oxygen in this state. Oxygen is absorbed from 400°C, and nitrogen from 600°C, and there is a large amount of nitrogen and oxygen in the air. As the degree of oxidation increases, the color of the weld of the titanium tube changes, and the plasticity of the weld decreases. 

Titanium and titanium alloys are relatively stable, but during the process of welding titanium tubes, at room temperature, the liquid droplets and molten pool metal have a strong absorption effect on hydrogen, oxygen, and nitrogen. In the solid state, these gases act on them. As the temperature rises, the absorption capacity of titanium and titanium alloys for hydrogen, oxygen, and nitrogen also increases significantly. Titanium starts to absorb hydrogen at around 250°C, oxygen at 400°C, and nitrogen at 600°C. After these gases are absorbed, it will directly cause embrittlement of the welded joint, which is a very important factor affecting welding quality. The main reason is that as the elastic content of hydrogen in the weld increases, hydrogen is a very serious factor affecting the mechanical properties of titanium. The change in its content in the weld has a great impact on the impact performance of the weld. The amount of flaky or acicular TiH₂ precipitated in the weld increases. The strength of TiH₂ is very low, and the notch significantly reduces the impact performance of flaky or acicular TiH₂, while the change in its content in the weld has no obvious impact on its strength and plasticity. The hardness and tensile strength of the weld of the titanium tube increase significantly, and the oxygen content of the weld increases linearly with the oxygen content of argon. But the plasticity obviously decreases. Therefore, in order to ensure the performance of the welded joint, during the welding process, oxidation of the weld and the heat - affected zone should be strictly prevented.