Excellent tension properties of stainless steel with a 316L/17-4PH/17-4PH laminated structure fabricated through laser additive manufacturing

Laminated metal structures (LMS), which are metals with site-specific properties, exhibit great potential for practical applications. In this study, a stainless steel with a laminated structure of alternating 316L/17-4PH/17-4 PH layer is fabricated using a laser additive manufacturing (AM) technique. Heterogeneous structures in the LMS are observed in two distinct areas, the austenite area (AU) and the martensite area (MA), based on optical microscopy and backscattered electron images. In the electron backscattered diffraction images, the AU area can be divided into austenite and mixture layers, while the MA area represents the martensite layer. Owing to the AM fabrication process, heterogeneity of both the micro-hardness and chemical composition exists among the three layers, which leads to different austenite stabilities in each layer. The tension test results reveal an excellent strength-ductility synergy with stronger ultimate strength and larger elongation than the pure 316L structure produced by AM with the same printing process parameters. During tension testing, the laminated structure causes strain partitioning, which evolves with the applied strain and delays the strain localization process. Owing to the change in austenite stability compared with pure AM 316L, the transformation-induced plasticity effect (TRIP) is triggered successively, and the laminate structure extends the TRIP effect to large plastic strains. As a result, the present study verifies the potential of using AM design for LMS stainless steel and may offer a framework for re-exploring LMS materials and components.