Ultrasonic pulsed waterjet peening of Ti-6Al-4 V manufactured by laser powder bed fusion

Laser powder bed fusion (L-PBF) processed metal components invariably possess poor surface quality in their as-built state, along with high tensile residual stresses. In order to optimize the surface properties and mitigate the adverse effects of L-PBF fabrication, the implementation of an appropriate post-processing surface treatment is essential. In the present study, Ti-6Al-4 V samples were fabricated by the L-PBF method, and showed an initial surface roughness, Ra, of ∼17 μm with pronounced anisotropic tensile residual stresses. Ultrasonic pulsed waterjet (UPWJ) was subsequently applied as a novel and environmentally benign surface peening technique for the L-PBF Ti-6Al-4 V parts. Samples were UPWJ peened either in the as-built state or following machining, through either a milling or grinding step applied to the L-PBF samples. It is demonstrated that the post-peening roughness could be reduced to Ra ≤1 μm through surface machining following by UWPJ peening, which was accompanied by the introduction of substantial compressive residual stresses up to approximately −800 MPa. Machining of the L-PBF parts, followed by UPWJ peening, led to a significant enhancement in scratch hardness (HS p ), exhibiting a maximum improvement of approximately 23 %. The combined use of machining followed by UWPJ peening is demonstrated to be a practical strategy to achieve both enhanced surface properties and high compressive residual stress for post-processing of L-PBF fabricated Ti-6Al-4 V parts. • As-built PBF-LB/Ti6Al4V had high tensile residual stress and surface roughness • UPWJ peening was an effective post-processing method for PBF-LB/Ti6Al4V • Milling is recommended for surface preparation of the parts before UPWJ peening • Milling and UPWJ peening induced high compressive residual stress (−800 MPa) • A maximum improvement of 20 % in scratch hardness was achieved after UPWJ peening