On the surface integrity resulting from laser powder bed fusion of Ti6Al4V: Improvements by cavitation abrasive surface finishing

Abstract

As the manufacturing readiness level of laser powder bed fusion (L-PBF) advances, post-processing has become increasingly important for achieving net-shape components and to enhance surface texture and integrity. Apart from surface roughness, one concern is the unique morphology of printed surfaces with vertical, upskin, and downskin inclinations. In this study, we characterized the surface texture and integrity of L-PBF Ti6Al4V with respect to build orientation. In the as-built condition, the downskin surfaces possessed the highest roughness, the largest effective surface stress concentration(),Ktand the greatest presence of partially melted powder particles fused to the surface. Cavitation abrasive surface finishing (CASF) was adopted to improve surface quality, with consideration of the build orientation. The results indicated that CASF reduced roughness, lowered Kt posed by the surface texture, and introduced compressive residual stress regardless of the build orientation. Downskin surfaces were the most challenging to treat; they exhibited substantially greater Ktthan the other orientations after treatment (>2×) and lower compressive residual stress (50%). More extensive powder coverage of the downskin surfaces appears to shield the underlying substrate from abrasive attack and direct implosion of cavitation bubbles, which are central to the CASF treatment mechanism. The importance of orientation to the effectiveness of CASF treatment is discussed, as well as strategies to overcome this challenge. Overall, downskin surfaces require greater surface treatment intensity or duration to obtain the same degree of improvement.

Keywords

Additive manufacturing / Laser powder bed fusion / Post-processing / Residual stress / Roughness / Stress concentration / Surface treatment / Titanium

Funding

The authors gratefully acknowledge that support for this work was provided by the Joint Center for Aerospace Technology Innovation (JCATI) in Washington State. The authors also gratefully acknowledge support for this investigation from The Boeing Company through the Boeing Advanced Research Collaboration and from the Sugino Corporation, Ltd. Part of this work was supported by the Washington Nanofabrication Facility/Molecular Analysis Facility, a National Nanotechnology Coordinated Infrastructure (NNCI) site at the University of Washington with partial support from the National Science Foundation (NNCI-1542101 and NNCI-2025489).

Conflict of Interest

Dr. Dan Sanders declares that he is an employee of Sugino Corporation as a chief technical officer, which may be perceived as a conflict.

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