Super metal in a class of its own

October 2014 - When one considers titanium’s pedigree, those of us not trained in metallurgy might have a few questions. Why isn’t the seemingly “super” metal considered a superalloy? And in the spirit of fantasy football, how does the metal stack up in terms of actual performance, and why do so many engineers and material specifiers choose this metal to be the star player in their line-up?

As with any pedigree, titanium’s lineage merits a quick review. Discovered in Cornwall, England in 1791, titanium—found primarily in minerals such as rutile, ilmenite and sphene—is the fourth most plentiful element in the earth’s crust. Ore was first converted to titanium metal and commercially produced in 1936. Prized for its corrosion resistance, superior strength-to-weight ratio and non-toxicity, today the metal is found in … well just about everything from fireworks, fishing poles, paint and sunscreen to high-performance race cars, implants, rockets and ships.

Its exceptional properties make it an industrial material of choice, especially for commercial and military aerospace applications. A report posted in September by the U.S. Geological Survey National Minerals Information Center said commercial aircraft production is expected to remain the dominant consumer of titanium metal, projecting usage to climb to 40,400 tons by 2017.

“There’s some overlap in terms of applications between titanium and superalloys,” says a U.S. consultant for advanced materials. But performance characteristics aren’t what keep the white metal out of the running for the title of superalloy. 

“Superalloys are characterized by the alloy—primarily nickel, cobalt and iron-based,” the consultant explains. The term also refers to supersaturation, a chemical solid-liquid separation technique that takes an alloy in a liquid solution to a pure solid crystalline state for further processing.

“Titanium is in a class by itself,” he says. “This is due in part to the applications titanium is used for but also because of how the raw material is processed.” Processing requires an oxygen-free environment and a complex, high-energy extraction method. Driven by the development of new alloys, titanium is poised to see increased use in automotive, aerospace, rocket, chemical energy and medical applications. 

RTI International Metals Inc. is working with titanium aluminide, for example.  “RTI recently signed a long-term agreement with SNECMA to be a major supplier of titanium aluminide for production of low-pressure turbine blades in the new CFM LEAP engine to power the next generation of single-aisle commercial jets,” says Kathryn Jackson, chief technology officer. “This innovative material is finding its place in the commercial aerospace marketplace.”

The degree to which titanium aluminide will replace nickel alloys in these types of applications will be determined by the major aerospace OEMs, she says. Able to withstand very high temperatures, TiAl’s use will substantially reduce the weight of a low-pressure turbine blade compared with nickel-based alloy materials traditionally used in their production.

Superplasticity is another avenue of research and development for aerospace OEMs. “It would mean the ability to form titanium into shapes at a lower temperature without worrying about brittleness,” according to the advanced materials consultant. 

Companies are also developing lower cost processing techniques such as the Metalysis method, which reduces the amount of energy required to separate titanium from oxygen. It is based on the Cambridge FCC process discovered by three researchers at Cambridge University, Cambridge, England, in 1997. The Metalysis method has demonstrated the capability to produce low-cost titanium alloy powders. According to independent technology development and licensing company The Technology Partnership Melbourn, United Kingdom, the process has the potential to make titanium almost as cost effective as specialty steels. MM