Abstract
Laser additive technology (LAT) uses a laser beam which locally melts the target material surface. The technology has been widely used for high value and critical components mainly in the aerospace and the biomedical industries. Due to its favourable properties, titanium has become a workhorse metal, particularly the grade 5 titanium alloy (Ti-6Al-4V). Recent years have seen increased research and development studies on the application of the laser additive technology in the production of Ti-6Al-4V components. These ranged from free form fabrication, materials processing, manufacturing, maintenance and repairs.
Attempts to use the laser additive technology for the repair of cracks in Ti alloy components have been recently reported where V-grooves have been recommended. Further attempts to use narrow U-grooves for crack repairs were not successful and hence not widely adopted. There is limited published work on the use of narrow rectangular grooves for crack repairs in Ti-6Al-4V.There is therefore a need to further investigate the potential repairing of U-cracks using LAT. This research work established through experimental design, mechanical and metallographic characterization, a process that was used for the laser additive repair of cracks in Ti-6Al-4V components. The preliminary repairs were made without laser re-melting. They were analysed for defects using the optical microscopy (OM) and their macrographs revealed lack of sidewall fusion, lack of interlayer fusion, lack of intralayer fusion, unmelted powder and porosity.
The matrix used for the preliminary repairs was then optimised using the observations made during the preliminary phase. It was from this preliminary phase optimization that the final experimental matrix of the research was developed. Controlled laser re-melting, reduction of the spot size diameter and lowering of the scanning speed were introduced as main process parameters of the optimized matrix. The optimized repairs were further characterized using the optical microscopy (OM) and the scanning electron microscopy (SEM). The optimized repairs were observed to have very limited defects. The energy dispersive spectroscopy (EDS) analyses revealed that the deposits were dominated by Ti, Al and V which were the main compositions of the material. The Vickers microhardness tests, microhardness-tensile strength correlations and the Charpy impact tests obtained results confirmed mechanically sound repairs with good evolving microstructural properties...
M.Ing. (Mechanical Engineering)