Residual Stress Development of Laser Assisted Cold Sprayed Ni Alloy 718 Coatings

The repair of Ni-alloy components via cold spray has become an established area of research, due to the economic benefits of increased component service life. However, a better understanding of the fundamental material behaviours, and the new technologies required to overcome the challenges is required. Ni-alloy 718 coatings were produced via laser assisted cold sprayed (LACS) on Ni-alloy 718 substrates. Laser heating of the substrate surface increases the ductility via thermal softening, improving the metallurgically bonded region, and also providing in-situ annealing of the deposited material to reduce tensile stress build-up and prevent de-bonding. LACS coatings were produced at various track spacings, surface temperatures and number of layers. The deposition efficiency was measured and the coatings were assessed through SEM/EBSD analysis to determine coating quality, degree of particle deformation and re-crystallisation. Surface profilometry compares the different track spacings and its effect on surface roughness and waviness. Surface X-ray diffraction measures the residual stresses for different layers and surface temperatures. A track spacing of 3.5 mm performed the best, and provided the most even interaction with the laser. All coatings were well bonded with low porosity and displayed tensile residual stresses.