X-ray Computer Tomography and Microstructural Characterisation of Additive Structures for Advanced Repair of Aeroengine Components

Aero engines are operated under incredibly arduous conditions, with many components suffering from damage and/or wear. From a sustainability and cost perspective, it is essential that components which are either high value, resource intensive (contain rare earths etc.) or both, are repaired and returned to service so that their full expected service life is reached, if not exceeded where safe to do so. One technology that is being developed for the repair of high value, high integrity components is laser blown powder directed energy deposition (LBP-DED).

During the LBP-DED process a laser is used to create a melt pool at the targeted repair location, a constant stream of powder, carried by inert gas, is then focused using a nozzle targeted at the melt pool created. As the laser moves the melt pool solidifies behind the laser and a repaired layer is created. Successive layers of repair are then built up to produce the final deposit. The final deposit is usually then further processed e.g. heat treated, machined, polished to meet the final condition required of the repair. Using the microstructural assessment methodology and expertise already used at Manchester in previous studies of additive layer structures (including X-ray computer tomography techniques, EBSD and SEM/TEM), a detailed microstructural characterisation and understanding of the formation of defects within Material Addition (MA) deposits, and the relationship these defects have to the input powder, process parameters and mechanical properties of specific titanium and nickel alloys is required. Metallurgical analysis and the understanding obtained will support a key repair strategy that is being developed globally for all gas turbine engines in which this technology can be exploited.