Surface modification by combining extreme high-speed laser material deposition (EHLA) with simultaneous roller burnishing

This study investigates the fundamentals of the simultaneous coating and roller burnishing process as a novel approach for improving the surface and subsurface properties of EHLA-deposited material. The combination of EHLA and roller burnishing yields significant improvements in surface roughness, microhardness, and residual stress distribution. The residual heat from the EHLA process was observed to increase surface plasticity during simultaneous processing, significantly influencing the effectiveness of roller burnishing as a function of the tool center point (TCP) offset parameter Δz. Surface finish is most favorably affected at a moderate Δz of 4 mm, suggesting the existence of an optimal thermal window for surface smoothing. The highest hardness was achieved at the smallest offset (Δz = 1 mm), potentially due to precold deformation effects and stress-assisted martensitic transformation. In terms of residual stress modification, all burnishing strategies succeeded in transforming high subsurface tensile stresses into beneficial compressive stresses, which are expected to enhance bending fatigue performance. The TCP offset further allowed directional stress control, enabling differentiated axial and circumferential stress profiles. Further studies are required to explore the relationship between the observed residual stress profiles and the corresponding fatigue resistance of repaired components under service-relevant loading conditions.