Two Excellent Properties Of Titanium And Titanium Alloys

Titanium and titanium alloys have two excellent properties: high specific strength and excellent corrosion resistance, which is why titanium alloys are preferred in the aerospace industry, chemical industry, medical engineering, and leisure industries.

Specific strength and high-temperature performance:

Metals vary widely in density. Lithium has the lowest density at 0.5g/cm-3, while osmium and iridium have the highest density at 22.5g/cm-3. The density of 5g/cm-3 is the dividing point between light metals and heavy metals, so titanium with a density of 4.51g/cm-3 is the heaviest light metal. Although titanium is twice as dense as aluminum (a typical light metal), it is only about half as dense as iron or nickel (Fig. 1.1).

Only below 300 °C, the specific strength of carbon fiber-reinforced plastics is higher than that of titanium alloys (Figure 1.2). At higher temperatures, the specific strength of titanium alloys is particularly excellent. However, the maximum service temperature of titanium is limited by its oxidizing properties. Since titanium-aluminum compounds can partially overcome this shortcoming, they have become the focus of alloy development. Traditional high-temperature titanium alloys can only be used at temperatures slightly higher than 500 °C, while titanium-aluminum-based alloys are directly comparable to well-developed high-temperature steels and nickel-based superalloys (Figure 1.2).

Corrosion resistance:

Titanium and titanium alloys have good corrosion resistance. In addition to some examples summarized in the table below, it is very important to maintain the integrity of the titanium oxide film on the titanium surface and not be damaged it to ensure its good corrosion resistance; once the oxide film is damaged, at least there is a chance to get a repair. Therefore, titanium and titanium alloys have long-term corrosion resistance in oxidizing atmospheres, and the presence of a small amount of oxygen and water is sufficient to form a protective oxide film.

The corrosion resistance of titanium can be improved by adding inert metals (often palladium and ruthenium), nickel, and molybdenum, or by using corrosion inhibitors in the machine. Extensive corrosion databases provide information on the corrosion of specific alloys in different media.

Titanium is required to have excellent corrosion resistance in coastal/offshore applications. For reasons of mechanics, technology, and corrosion, new-generation offshore platforms have thousands of meters of titanium alloy transmission and supply pipelines.