A SUPER-resilient steel that is packed with nanoparticles could make it possible to mass-produce hugely tough mechanical components, such as turbine blades that can last 1000 times longer than conventional ones. The steel is laced with the particles during the normal manufacturing process, making the material cheap and easy to produce.
The team that made the steel, at the Steel Research Center in Tsukuba, north of Tokyo, hopes it will be useful in high-temperature industrial applications, such as making boiler tanks or turbine blades for electricity generating stations. The metal鈥檚 resistance to being deformed even at high temperature and pressure could make plants that use it cheaper to build and run, by allowing them to use thinner, lighter components, or by extending the components鈥� lives.
The property the Japanese scientists most wanted to eradicate from their steel was 鈥渃reep鈥�, the slow deformation that normally occurs when a metal is subjected to pressure and heat. Even at room temperature, metals can deform as a result of imperfections in their microscopic structure. Slippage occurs along boundaries between the tiny grains that form the metal. The higher the temperature or pressure, the more rapidly this happens.
Advertisement
Introducing very hard, very small particles into the metal can stop creep by 鈥渏amming鈥� the grains in position. In previous attempts to make creep-resistant steel, yttrium oxide particles were added to the mix of molten steel. 鈥淭he oxide particles are introduced by complicated mechanical alloying techniques,鈥� says the Japanese team in this week鈥檚 Nature (vol 424, p 294). 鈥淎s a result, the production of large-scale industrial components is economically unfeasible.鈥� What鈥檚 more, the yttrium oxide nanoparticles become segregated during the cooling process. 鈥淭he particles just sink,鈥� says Jo茫o Quinta Da Fonseca, a steel expert at the University of Manchester Institute of Science and Technology.
The Japanese team鈥檚 solution was to use carbonitride nanoparticles, which consist of thermally stable and very rigid molecules that form strong bonds with steel impurities such as niobium and vanadium. The crucial difference is that the constituent elements of carbonitride 鈥� carbon and nitrogen 鈥� already exist in steel.
By a trial-and-error process in which they varied the carbon content of the steel and the way in which the mix was heated and cooled, the Tsukuba team has found that they could get the carbonitride nanoparticles to form during the manufacturing process itself. And because the nanoparticles are produced during the annealing process, in which steel is heated and cooled to strengthen it, they remain suspended and evenly spread throughout the metal.
The technology should lead to more creep-resistant steels and affordable components, the team says. There is just one snag. The researchers have yet to show that their super-strong steel is resistant to corrosion and is not too brittle, says Fonseca. 鈥淭hey have solved one problem but still have to show their material can do the rest,鈥� he says.