MICHAEL PHELAN / LONDON
Titanium matrix promises dramatic weight savings without compromising on strength
UK research and technology group Qinetiq has developed aircraft bolts made from titanium metal matrix composite (Ti-MMC), with weight savings of over 30% on stainless steel. The material combines silicon carbide (SiC) fibres with high-temperature resistant metal, and is twice as stiff as stainless steel, says Qinetiq sales manager Stephen Kyle-Henney.
Qinetiq has achieved a breakthrough in the bonding technology, he adds. The bolts consist of a titanium core to which a circumferential layer of Ti-MMC is applied. Traditional 316L stainless steel is used for the bolt-head corners and the bolt thread - areas where titanium has previously performed poorly. The bolts are 28mm (1.1in) in diameter and 100mm long, and weigh 265g (9.3oz), against 418g for 316L stainless steel bolts.
The composite is made by diffusion bonding matrix-coated fibres with metallic layers in an isostatic press at temperatures of up to 1,000ºC (1,830ºF), depending on the alloy. The coating is crucial to the bonding process, says Kyle-Henney - the mechanism involved being one of metal-to-metal bonding. Qinetiq has the only coating plant, and is the only source of SiC fibre in Europe.
The bolts are the first application of the company's Ti-MMC material in aircraft structures. Kyle-Henney says the technology could be incorporated in aircraft primary structure and landing gears within "two to five years". Qinetiq is working with Rolls-Royce, which is interested in the technology for developing bladed-ring engine components.
Meanwhile, US company Atlantic Research (ARC) is manufacturing, at its Wilmington, Massachusetts facility, a titanium matrix composite (TMC) piston for the divergent nozzle actuator on the Pratt & Whitney F119 engine for the Lockheed Martin/Boeing F-22 Raptor. The piston rod has the strength and stiffness of stainless steel, but weighs 40% less. ARC last year signed an exclusive development deal with Goodrich for TMC landing gear components.
Source: Flight International
