What is Titanium

Titanium is a silver-white transition metal and is considered a rare metal because it is relatively dispersed in nature and difficult to extract. But in fact, titanium is relatively abundant, ranking tenth among all elements. Titanium ore mainly includes ilmenite and rutile, which are widely distributed in the crust and lithosphere. Titanium is also present in almost all living things, rocks, water bodies and soil.

Physical Properties

Titanium has metallic luster and ductility. The main characteristics of titanium are low density, high mechanical strength, and easy processing. The plasticity of titanium mainly depends on purity. The purer the titanium, the greater the plasticity.

Chemical Properties

The chemical properties of titanium have an extremely close relationship with temperature, form and purity. Dense titanium is quite stable in nature, but powdered titanium can cause spontaneous combustion in the air. The presence of impurities in titanium significantly affects the chemical properties, mechanical properties and corrosion resistance of titanium. The chemical activity of titanium at room temperature is very small, and it can react with a few substances such as hydrofluoric acid. However, the activity of titanium increases rapidly when the temperature increases, especially at high temperatures, titanium can react violently with many substances.

The Role of Titanium in Superalloys

In nickel-based superalloys and iron-based superalloys, 10% of titanium will enter the γ solid solution to play a solid solution strengthening effect.

The remaining 90% will enter the γ' precipitation strengthening phase to replace the aluminum atoms in the γ' phase to form Ni3(Al, Ti) (Limited to precipitation strengthened superalloys, such as Inconel 718, Inconel X-750, Incoloy A-286, etc.). Increasing the content of titanium can increase the amount of γ' precipitation strengthening phase. In the article introducing the role of aluminum, we mentioned that the increase of aluminum can also increase the amount of γ' phase, but if the content of aluminum in the alloy is too high, it will affect the creep strength of the alloy. The addition of titanium solves this problem well.

Figure 2
The Effect of Titanium Content on Yield Strength

In addition, the ratio of titanium to aluminum (titanium-aluminum ratio) also affects the strengthening effect of the γ' phase. The higher the titanium-aluminum ratio, the better the precipitation strengthening effect of the γ' phase. However, if the ratio of titanium to aluminum is too high, the performance of the alloy will be unstable.

Figure 3
Influence of the Change in the Ratio of Titanium to Aluminum on the Lattice Mismatch

Conclusion

In superalloys, titanium mainly plays a role of precipitation strengthening, which can further enhance the strengthening effect of the alloy on the basis of aluminum.

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