Effect of gas and impurity contamination on welding performance of titanium and titanium alloy

Titanium and titanium alloys are relatively stable at room temperature. But in the test table, in the welding process, liquid droplet and molten pool metal has a strong absorption of hydrogen, oxygen, nitrogen, and in the solid state, these gases have acted with it. With the rise of temperature, titanium and titanium alloy absorption of hydrogen, oxygen, nitrogen capacity also increased significantly, about 250℃ began to absorb hydrogen, from 400℃ began to absorb oxygen, from 600℃ began to absorb nitrogen, these gases are absorbed, will directly cause welding joint embrittlement, is a very important factor affecting the quality of welding.

(1) Hydrogen is the most serious factor affecting the mechanical properties of titanium among gaseous impurities. The change of hydrogen content in the weld has the most significant effect on the impact performance of the weld. The main reason is that the amount of flaky or needle-like TiH2 precipitated in the weld increases with the increase of hydrogen bomb content in the weld. The strength of TiH2 is very low, so the action of flake or needle HiH2 is notched, and the impact performance is significantly reduced. The effect of the change of hydrogen content on the increase of strength and reduction of plasticity is not very obvious.

(2) the effect of oxygen oxygen in titanium α phase and β to have a high degree of melting, and can form a gap solid deep phase, the use of titanium crystal wound seriously distorted, so as to improve the hardness and strength of titanium and titanium alloy, so that the plasticity is significantly reduced. In order to ensure the performance of welding joint, the oxygen content in base metal and welding wire should be limited in addition to preventing the main oxidation of welding seam and heat affected zone during welding.

(3) the influence of nitrogen under the high temperature of 700 ℃ above, nitrogen and titanium play role in the formation of rigid titanium nitride (riN) and nitrogen and titanium gap formation of solid solution caused by lattice slanting Noah, than is caused by the amount of oxygen is more serious, therefore, nitrogen of industrial pure titanium weld tensile strength and hardness, reduce the plastic properties of the weld is more significant than oxygen.

(4) carbon is also a common impurity in titanium and titanium alloy. The experiment shows that when the carbon content is 0.13%, the carbon is deep in α titanium, and the weld strength limit is improved and the plasticity is decreased, but not as strong as the effect of oxygen and nitrogen. However, when the carbon content of the weld is further increased, the network TiC appears in the weld, and the number of TiC increases with the increase of carbon content, so that the weld plasticity decreases sharply, and it is easy to crack under the action of welding stress. Therefore, the carbon content of titanium and titanium alloy base material is not more than 0.1%, and the carbon content of weld is not more than the carbon content of base material.