How Much Do You Know About The Titanium Production Process? (one)

Titanium has to go through many processes to get from ore to finished product. Depending on the final application, the number of steps taken will vary. Titanium used in high-end car exhaust, hip implants or watches does not require the same rigorous management of microstructure as it is used in aviation, where the risks and consequences of failure are much greater.

Kroll process

Regardless of the end use, titanium must first be removed from the ore and turned into pure titanium.

This is done by treating titanium dioxide made from ilmenite or rutile through the Kroll process. The output is sponge titanium that has been purified, melted, and alloyed with other metals. It may then undergo further processing into so-called master alloys, which are then turned into ingots that can be made into bar, plate, sheet or wire as a common mill product.

Kroll Process It is a multi-stage reaction started in a fluidized bed reactor. Purified titanium dioxide TiO2 is oxidized with chlorine to form titanium tetrachloride, TiCl4, affectionately known in the industry as "tickling". The reaction is carried out at 1000°C. From there TiCl4 and other metal chloride impurities are fractionated to produce a pure TiCl4 mixture.

It is then transferred to a separate stainless steel reactor, where it can be mixed with magnesium during the second half of the process. The reaction was carried out in an argon atmosphere preheated at 1000 °C. The resulting titanium(III) and titanium(II) chlorides slowly reduce over several days to form pure titanium and magnesium chloride.

The remaining magnesium chloride is then recovered by separating it back into its constituents. And titanium, now in "sponge" form, is gouged out, crushed into smaller pieces, and then pressed together to form a uniform piece. It is ready to be melted as an electrode in a vacuum arc remelting (VAR) process.

Vacuum Arc Remelting Titanium - Alloying

VAR has been the dominant method of titanium alloy fabrication since the 1950s. This is a process used to make high-performance titanium products. VAR precisely controls the melting and solidification of the melt to reliably produce high-quality finished alloys of extremely high purity.

Most titanium alloys go through this process at least twice. This is to ensure an acceptable level of consistency throughout the metal. This process is still used in industrial applications. In the second half of the 20th century, triple VAR was mandated for aerospace use in response to defects in metals. Although over the past decade it has begun to be replaced by electronic cold hearth remelting for aerospace alloys.

The VAR process takes place in a large cylindrical crucible. An electrode hangs from the top, and a direct current of several thousand amps is passed through it, causing it to melt and drip to the bottom of the chamber where the alloy recombines. In the case of Ti 6AL-4V, aluminum and vanadium are added.

Electron beam cold furnace remelting

Cold hearth melting effectively addresses one of the deficiencies of the VAR process, the ability to efficiently remove both high and low density inclusions (HDI and LDI) from the melt. It is also used to dispose of waste chips generated during machining. A vacuum is formed in a water-cooled copper furnace. A high-temperature electron beam is then focused on the titanium feedstock (a mixture of sponge, VAR metal and chips) placed at the rear of the furnace. Molten titanium drips into the melting zone, then flows into the refining tunnel, and then pours into the mold where the metal crystallizes. Volatile compounds evaporate, i.e. oxygen and nitrogen inclusions, while dense tungsten carbide from the cutting tool sinks to the bottom. The end of the ingot is then machined away, leaving behind the titanium alloy.