Chemical-Cavitation Approach to Improving the Surface Texture and Surface Integrity of Laser Powder Bed Fusion Additive Manufactured Components

Laser powder bed fusion (LPBF) additive manufacturing offers several advantages over traditional processes for the manufacture of component parts. However, the rough surface texture and tensile residual stress resulting from LPBF are often unacceptable in engineering applications. Post-processing is necessary to achieve the surface quality required for stress- and safety-critical applications. The industry standard involves chemical milling, but the process is incapable of introducing compressive residual stress and the toxic chemicals which are used pose an undesirable risk. Although peening processes involving shot or water can introduce the desired residual stress, they are not effective at improving the surface finish. Here, we introduce a hybrid approach involving a proprietary environmentally-safe chemical treatment followed by Cavitation Abrasive Surface Finishing (CASF). The latter utilizes a high-pressure cavitating water jet and an abrasive slurry to achieve a combination of material removal, smoothing and localized deformation to improve the surface integrity of component parts. Results from preliminary treatments performed on Ti6Al4V targets produced by LPBF show that the hybrid approach is very effective at reducing the surface roughness and the apparent stress concentration posed by the surface morphology. Compressive residual stress in the treated surfaces exceed 400 MPa and the process appears equally effective on vertical, 45 degree upskin and downskin surfaces, reducing the complexity of tuning treatments for these specific surfaces. This new hybrid approach could help mitigate the risk of surface flaws, rendering substantial improvements to the component reliability and fatigue life of LPBF components. Details regarding the changes in surface texture and residual stress will be discussed, along with the dependence of the printed surface morphology and the importance of tuning the initial chemical treatment for the desired application.