Inside the rare race to make single-crystal jet engine turbine blades

Single-crystal turbine blades, grown rather than cut from metal, are among aviation's most specialised parts. Developed in the 1960s, they sit inside jet engines and withstand mechanical stresses and temperatures above 1,500C. Only a handful of companies worldwide can make them, and the full process has been perfected in just five countries, including the US and UK.

Growing one crystal instead of many

To make one, engineers cast a molten metal alloy into a blade shape, then cool it slowly from one end to the other over hours so that a single crystal, or grain, forms. Ben Fifoot, a manufacturing engineer at Rolls-Royce, describes the task as “fight the laws of the universe”. Without careful control, the alloy would solidify into many jumbled grains. A small spiral called a pigtail helps choke the flow of solidifying crystals so one takes over; the spiral is cut off after casting. Fifoot says the number of turns or angles may need adjusting to get a more favourable grain.

A small club of manufacturers

Rolls-Royce, GE and France's Safran are among the few firms to have mastered the process. In September, GE Aerospace announced it would acquire its turbine blade supplier for $11.75bn (£8.78bn). Neither company responded to BBC News' requests for comment, but the move has been described as an effort to secure supply of critical components. In March, Rolls-Royce said it would invest more than £19m in its Rotherham blade casting facility. Rolls-Royce blades are used in engines including the Trent XWB-84, which powers the Airbus A350-900, and the Trent 1000 XE, for the Boeing 787.

Cooling, coatings and weight

Blades are protected by special ceramic coatings and cast with tiny channels that let cooler air form a protective film. Paul Withey, of the University of Birmingham and a former Rolls-Royce employee, says the industry is trying to make these cooling passages more intricate because more turbulent cool-air flows remove more heat. Manufacturers also try to reduce blade mass: Fifoot says lower weight allows an engine to run more efficiently, use less fuel and spin faster and hotter. If a blade forms two crystals instead of one, the alloy must be reprocessed so the material can be reused.

China's uphill effort

China hopes to become the sixth country to master the whole single-crystal blade casting chain. A May report quoted an engineer at the AECC Beijing Institute of Aeronautical Materials claiming China had a single-crystal alloy “superior to or equivalent to the second-generation single-crystal superalloys widely used in Europe and the US”, and claimed it costs less to make. But aviation writer and consultant Bill Sweetman says the West has a “huge advantage” because most commercial airliner production, supply chains and recent innovation are clustered there, and Western manufacturers have long safety records. China must compete across aircraft manufacturing, not just blades, he says, calling it a long, uphill struggle. Demand for aircraft is high and already straining supply chains. Withey suggests Airbus or Boeing could launch a new short-haul plane in the next few years, prompting the other to follow and triggering a “bun fight” over engine suppliers and, by extension, turbine blades.

Source: BBC Technology.