Strength, microhardness, and microstructure analysis of 316L stainless steel manufactured via hybrid laser wire and laser powder bed additive

Abstract

Additive manufacturing techniques including laser powder bed fusion (LPBF) and laser wire direct energy deposition (LWDED) can be integrated into a hybrid additive manufacturing (AM) process. Combining LWDED with LPBF leverages their complementary strengths to achieve optimized part geometries and properties, as well as making it possible to repair LPBF parts using LWDED. In this study, LWDED 316L SS blocks were deposited onto both LPBF 316L SS and conventional cold-rolled and annealed (CRA) 316L SS substrates to investigate the resulting microstructure and properties when these techniques are combined. Mechanical properties, including microhardness and tensile strength, were compared with electron backscatter diffraction (EBSD) characterization of the microstructure. The tensile strength of the hybrid AM LPBF-LWDED (σy = 338 MPa) was superior to that of the CRA-LWDED AM (σy = 326 MPa) or LWDED (σy = 312 MPa) alone. The microhardness of the LWDED region was greatest at the interface with the CRA substrate (210 ± 5 HV) and gradually decreased along the build direction. In contrast, the LWDED microhardness at the interface with the LPBF substrate (193 ± 6 HV) was comparable to the bulk LWDED value and remained constant along the build direction without significant variation. The disparity in the LWDED microhardness among the two substrates was attributed to a faster cooling rate, due to higher thermal conductivity in the CRA substrate than in LPBF. These results demonstrate a successful path towards LPBF-LWDED hybrid AM and its advantages over conventional CRA-LWDED.