Marshall Aerospace, the Cambridge aircraft refitting company, asked TWI to help with refurbishment of critical wing components. Badly worn titanium alloy flap and slat tracks, from Lockheed Tristar aircraft, have been repaired by TIG welding and high velocity oxyfuel (HVOF) spraying at TWI.
The relative scarcity and high cost of replacement parts makes repair an attractive alternative. However, the tight schedules that Marshall Aerospace is required to operate during a refit demand that these parts have to be stripped from the aircraft and refitted typically within 48 hours.
On the first occasion that TWI undertook this repair, it became clear that finding a suitable TIG welding consumable for this titanium alloy was impossible. It was agreed that consumable could be made by machining samples from a scrapped component, which would also give the best compositional match.
The TIG weld repair was completed manually with argon gas shielding. After grinding back to the required dimensions, the bearing surfaces were grit blasted, cleaned and HVOF sprayed with a thin coating of cobalt-tungsten carbide.
The final coating provides a significantly more wear resistant finish than the original titanium alloy.