Microstructure change and corrosion resistance of selective laser melted Ti-6Al-4V alloy subjected to pneumatic shot peening and ultrasonic shot peening

Abstract

Titanium alloys fabricated by selective laser melting (SLM) are typically subjected to post-treatments, such as shot peening, to improve the mechanical properties. However, the same Almen intensity may correspond to various combinations of peening parameters, which will generate different microstructures and comprehensive properties. Herein, the SLMed Ti64 alloy was treated by pneumatic shot peening (SP) and ultrasonic shot peening (USP) under the same Almen intensity of 0.2 mmA, investigating the changes of the microstructure and corrosion resistance. The average surface roughness (Ra) of the SPed sample was 1.806 μm, which was significantly higher than those of the USPed samples (0.942 μm and 0.999 μm). The USP and SP treatments led to the surface plastic deformation and grain refinement, while the SP produced a smaller crystallite size. The SP treatment led to the biggest surface and max compressive residual stress, which were −654.0 MPa and −805.5 MPa, but the USP resulted in thicker compressive residual stress layers. The USPed sample reached the highest microhardness (443.2 HV0.025) and the thickest hardened layer (247.8 μm). The USP and SP samples offered superior corrosion resistance, but the USPed samples showed higher corrosion potentials and lower corrosion current densities.