In this project, Cambridge-based advanced coatings company Tecvac worked with Dr Adrian Leyland and Prof Allan Matthews (Leonardo Centre, University of Sheffield), bearing manufacturer NMB-Minebea and Airbus UK to develop a coated titanium bearing technology that could significantly reduce the weight of new Airbus aircraft. The aim was to replace steel/bronze pintle (and other) bearings on A350/A380 aircraft with a surface-engineered titanium-on-titanium alternative. There are typically over 2,500 steel bearings on each Airbus aircraft so finding a solution had the potential to save hundreds of kilograms (ie. at least the weight of a typical family plus luggage) as well as reducing the aircraft’s carbon footprint through reduced CO2 emissions.
Replacing all the steel bearings with a strong Ti-6Al-4V titanium alloy was predicted to reduce the weight of an aircraft by at least 400 kg but the load-carrying capacity and wear resistance of the alloy surfaces needed to be drastically improved. A titanium bearing in a critical application such as aircraft landing gear would quickly wear out under the high loads experienced during normal operation.
R&D staff at Tecvac and the Leonardo team knew that simply applying a hard and wear resistant PVD coating alone was not a viable solution. The relatively soft titanium alloy would provide little load support for the hard coating, which would eventually crack (and the debris produced would accelerate bearing failure).
In close collaboration with Tecvac the Sheffield University research staff developed a new ‘duplex’ plasma diffusion treatment process that improves the resilience of titanium alloy surfaces. They then added a hard-wearing ceramic nitride coating to the improved titanium bearing surface. Together, this provided the lightweight (and durable) solution Airbus was looking for.
The market for this new technology is potentially very large. Manufacturers around the world are eager to reduce the weight of aeroplanes in order to increase fuel efficiency and conform to impending emissions standards. Airbus has already placed a £19m order for one type of wing structure bearing attaching the main landing gear for the new Airbus A350. Once these have been upgraded to titanium alloy, attention will turn to the thousands of other bearings on various Airbus aircraft. Work will not be restricted to new planes. As they wear out, existing bearings on planes already in service can be replaced too - with little or no modification required.
This work was supported by funding from the UK Technology Strategy Board (TSB)