Abstract
A hybrid fabrication method combining additive manufacturing (AM) and ultrasonic impact treatment (UIT) techniques was developed to improve the microstructure and mechanical properties of additive manufactured metal parts. Experimental and numerical methods were conducted to analyze the stress and strain fields of ultrasonic impact on additive manufactured parts. Laser metal deposition (LMD) technique was applied to prepare the 304 stainless steel (SS) samples and then the samples were post-treated by UIT. Considering high strain rate effect of metallic materials in the UIT process, the dynamic hardening properties of the as-deposited 304 SS sample were experimentally measured using a split Hopkinson pressure bar (SHPB) technique. The strain rate controlling factors and stress-strain relationship of the as-deposited sample in the SHPB tests were theoretically analyzed. The dynamic and high transient impact-rebound-impact process of UIT including the pin velocity, stress field and plastic strain field were investigated numerically via a three-dimensional finite element model. The impact stress field parameters such as the magnitudes and directions of principal stress and principal shear stress were investigated to further analyze the plastic deformation behavior of the deposited sample. The experimental results of plastic deformation zone obtained from optical microscopy, electron backscatter diffraction (EBSD) and microhardness testing are in good agreement with the numerical results. Both the experimental and numerical results confirm that UIT can effectively improve the performance of additive manufactured metal parts.
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