Sterling strength-to-weight ratios and corrosion resistance make titanium ideal for building lightweight vehicles. The problem has always been cost; it takes great quantities of energy to smelt titanium, which can push material costs as much as 50 times higher than steel.
So it's no wonder that use of the light metal has been limited so far to the likes of and supercars. Similarly, near-net-shape powder-metal (PM) titanium parts are rare, and for the same reason; titanium powders sell for from $200 to $400 per kg ($90 to $180 per lb).
But titanium powder prices may start to fall in a year or two if a new energy-saving smelting technology is successfully commercialized by Metalysis, a UK-based specialty metals maker, according to Kartik Rao, the company's Director of Business Development. The investor- and grant-backed spin-off of Cambridge University was established in 2001.
“Our process is different because it uses electricity to separate the metal from metal oxides,” Rao said. “It could reduce the cost of titanium powder production potentially by as much as 75% or more,” making titanium almost as cheap as specialty steels, and thus competitive with aluminum and steel—at least in higher-end products.
Metalysis’ potentially game-changing process is substantially less energy- and labor-intensive than the high-cost Kroll process, the traditional way titanium has been made since the mid-1940s, said Rao. The conventional route relies on pyrometallurgical processes—high-temperature chemical reactions with reactive metals—to remove titanium from the titanium oxide ore.
The company’s novel electrowinning technique uses an electric current to directly separate metal and oxygen atoms in the solid state—no melting needed. Covered by 24 patents, the process runs at lower temperatures and is significantly more environmentally sustainable than the conventional process, according to the company.
The so-called FFC Cambridge process was developed at the university by Derek J. Fray, Tom W. Farthing, and George Z. Chen in the late 1990s. After more than a decade of development to commercialize it, Metalysis scientists and engineers have learned to make titanium powder in a single step, thus bypassing the Kroll process as well as several remelting, consolidation, and rolling procedures that typically proceed atomization into fine metal powder.
3D-printing titanium parts
Some of Metalysis' first test batches of titanium powders were recently 3D-printed into near-net-shape auto components by a group of researchers at Sheffield University’s Mercury Centre in South Yorkshire, which specializes in metal processing and powder-based manufacturing. The PM titanium parts, once heat-treated to relieve residual micro stresses and strains left from the laser heating, display 80% of the strength of cast and annealed Titanium 4-6 alloy components, said center director and metallurgist Iain Todd.
His team built the demonstration parts—impellers and turbochargers, as well as aerospace airfoils—using a small-scale Renishaw AM125 laser-based printer that the researchers had modified to operate at higher temperatures. “The powder processes beautifully into fully dense components, which was a bit of a surprise,” said Todd. “It’s not quite aerospace-grade yet, but getting there.”
Additive manufacturing methods such as 3D printing "have gotten a lot quicker in recent years,” Todd noted. With cheaper powder feedstocks, they can become more price-competitive with standard subtractive techniques that require costly tooling to shape components out of billets, leaving masses of waste. If titanium powder prices were to drop to commodity levels, the pathway would open for 3D-printing-affordable titanium car parts in first low, then medium, production volumes.
“If the materials costs are right, then there’s value in the design changes that provide better performance and still save money,” said Todd, adding, “This is a classic disruptive technology.”
“So far, Metalysis has 3D-printed some aerospace components using our titanium alloy as a ‘proof of concept,’” Rao said. “Although we have printed some turbine guide vanes, our focus will be on noncritical components. We are working with the University of Sheffield to demonstrate the 3D printing and have interacted with potential end users on a confidential basis as well.”
Building on sand
Reduced energy requirements constitute part of the process’ cost savings, but another major component derives from “the basic titanium oxide feedstock, rutile sand, which is an inexpensive and plentiful natural ore source,” he explained. “It’s actually a derivative of prehistoric alluvial beaches found in places like Australia, South Africa, Sierra Leone and Ukraine.”
The cost-effective reduction process starts with sintered rutile sand (titanium oxide), which serves as the cathode. The anode is made of carbon. Both swim in a bath of molten calcium chloride salts at 800 to 1000°C (1500 to 1800°F) that acts as an electrolyte, permitting current, in the form of migrating oxygen ions separated from the metal oxide, to travel from cathode to anode. There, the ions react with the carbon to form carbon dioxide gas while the cathode gradually transforms into metal. The method is essentially one-step. The salts can be recycled.
“We’re now getting a 40- to 50-micron powder,” the size range that is suitable for powder metallurgy, Rao said. The resulting “nodular/angular particles flow well enough, but recently we started processing them into spherical powder and that’s what we’re using for the 3D printing.”
The production process is flexible regarding powder size, which is determined by the size of the granulated feedstock.
Alloying can be accomplished easily, Rao explained, because technicians can simply mix metal oxide powders such as titanium oxide and tungsten oxide, and “solid solutions form via atomic mixing even before they enter the reactor.” Metals with significantly different densities or melting points can be alloyed because the process is conducted in the solid state.
“We can solve a lot of these issues at the feedstock stage,” said Rao.
First tantalum, now titanium
The basic FFC electrolytic reduction platform can also be used to produce a variety of other metals besides titanium. In fact, Metalysis’ titanium powders were produced in trial runs at the company’s tantalum plant. Tantalum, an almost inert metal, is an ingredient in medical equipment and electronic capacitors used in engine controls and other car electronics. In the future, the company may produce rare-earths and other specialty metals as well.
“Our focus is now mostly on tantalum,” said Rao, “but we’ve turned more attention to titanium.” The big prize was always titanium. Even at its current price, about $4.5 billion worth of titanium mill products are sold each year.
Recent reports indicate that Metalysis seems to be well on its way to discussions with financial institutions and industry players to arrange funding for a titanium production plant that could cost anywhere from $50 to $500 million. “At this stage," Rao said, "we are trying to fully understand the technical and business risks of building a plant, and how to mitigate them.”