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Titanium is neither a precious metal nor rare, yet among industrial metals it has the reputation for being very expensive. It's the fourth most abundant metallic element and the ninth most abundant of all the elements in the earth's crust. Its commercially useful oxide ore occurs in the minerals rutile and ilmenite and numerous iron ores, and exploitable ore deposits are liberally scattered around the world in Australia, Canada, India, Malaysia, Norway, Russia, South Africa and the U.S. But due to its properties and high cost it has often been referred to as unobtanium.

With such great abundance why is titanium so expensive?

There are two primary reasons. First, the cost of chemically extracting titanium from its ore, then turning it into ingots is very high. Second, processing the metal from ingot to finished mill products generates large amounts of expensive waste.

Typically, 15 – 40% of the starting ingot material becomes scrap during required conditioning steps. Titanium's reactivity at high temperatures with oxygen and nitrogen contributes to the high cost in both cases.

Among major structural metals, titanium is the youngest. Unlike iron, of which the first known artifacts shaped by humans date to approximately 3200 BC, titanium was not even identified as an element until the late 1700s. And it was not until 1937 that Luxembourg inventor Dr. Wilhelm J. Kroll developed a process demonstrating that it could be produced commercially. The Kroll process chemically reduces titanium tetrachloride with magnesium. Producers then either acid leach or more commonly vacuum distill the resulting sponge-like material to remove impurities and form the metal. After Kroll's demonstration, another eleven years of process development was required by the U.S. Bureau of Mines before the first commercial titanium sheet was produced.

How Titanium Is Produced

Titanium metal is produced from ore to mill product in three general steps:

  • the chemical reduction of ore to sponge (the agglomerated granules resemble a sea sponge);

  • melting the sponge (often in combination with titanium scrap) to form an ingot;

  • and lastly, converting the ingot into saleable mill products.

The chemical process of refining the ore to metallic sponge is a complicated multi-step, high temperature batch process that is labor, energy and capital intensive. In spite of attempts to improve upon it, the process has remained basically the same since its inception.

Turning sponge into ingot is complicated and regardless of which melting method is used—vacuum arc re-melting (VAR), electron beam cold hearth melting (EBCHM), or plasma arc melting (PAM)—it is highly energy intensive. Like the ore chemical reduction process, it must be done in a vacuum or inert atmosphere to control reactive contamination that would compromise the metal's structural integrity.

As-forged incoming material displaying cracks and alpha case, requiring conditioning.
The same material fully conditioned by the MetCon process, ready for forging or rolling. Crack tips have been removed and more parent material preserved than by traditional conditioning methods.

The last step, thermo-mechanical conversion of titanium ingot into mill products—bar, plate, sheet, rod, and so on—is done in much the same manner as other metals. But, again, the metal's highly reactive nature plays a critical role. The metal is heated to the appropriate temperature, processed to the next incremental size or shape (mainly via forging or rolling), allowed to cool, conditioned and inspected. Then the process is repeated until the final mill form and size is reached. However, when exposed to air at high temperatures the metal is reactive, absorbing additional oxygen and nitrogen, forming a hard, brittle, shell-like oxygen-enriched phase of the metal called “alpha case” over the entire surface. The mechanical properties of the alpha case layer are greatly reduced from the parent metal. Additionally, as the metal cools, surface cracks form which can extend into the material to a depth of 5% or more, and they too are covered with alpha case. Unless the alpha case layer and the cracks are removed, additional thermo-mechanical processing will simply drive the cracks and defects more deeply into the metal, compromising its performance and fatigue properties, causing even greater yield losses at the next conditioning step.

Conventional Conditioning

The process for removing alpha case and surface defects and preparing the metal for the next hot forming step is called “conditioning”. Alpha case is tenacious and hard and the most widely used method of conditioning titanium traditionally has been grinding, often followed by acid pickling.

The removal of metal by grinding with a rotating abrasive wheel is a slow process governed by physics. The arc of the grinding wheel can only contact the material being conditioned in a small patch. The contact patch pressure must be carefully controlled as the wheel rotates and moves laterally. Too little pressure and the process is inefficient. Too much pressure generates excessive heat creating a new layer of alpha case. The round wheel can only remove a narrow strip of material as it moves the length of the surface. It then indexes for the next pass and repeats the process until the entire surface has been reduced by the depth of the wheel's arc. The total surface grinding process is repeated as many times as required until the surface appears crack-free. Pickling is often subsequently used to clean the surface and reveal cracks and other defects covered over and hidden by metal smeared during grinding. The material is then either returned to the auto grinder for additional grinding, or hand ground if the revealed defects are shallow. Both conditioning methods are dangerous and generate hazardous waste.

The industry also sometimes uses machining, either bar turning or milling, to condition titanium, but the machining process is more costly, even slower, and removes excessive prime material. Machining is usually only employed where the producer requires a smoother surface than can be obtained from grinding and/or pickling, such as when an ultrasonic inspection follows the conditioning step.

These conventional conditioning processes have been used virtually since the beginning of titanium production because they worked and were pretty easily understood. Of course, they were developed and have been fine-tuned by different producers to meet their own needs (the amount of conditioning required after hot working depends on numerous factors including melt source and method, hot process and amount of reduction). But the basic processes have been accepted and have not changed much since the early days of titanium production. Accordingly, conditioning processes have remained relatively low-tech and until recently no one has figured out a way to improve upon them. Yet the cost of the material lost to waste in conditioning is one of the largest contributors to the cost of the material sold.