Microstructure and mechanical characteristics of multi-layered materials composed of 316L stainless steel and ferritic steel produced by direct energy deposition

Abstract

In the present study, we investigated the feasibility of fabricating multi-layered materials (MLMs) composed of austenitic stainless steel (316L) and ferritic steel (P21) using one of the additive manufacturing technologies, direct energy deposition (DED). With DED, an intermediate buffer layer is introduced between a bottom (P21) and a top (316L) layer. The relative compositions (wt%) of the three layers are 0:100, 50:50, and 100:0. Microstructure and mechanical properties were characterized via optical microscopy, electron backscatter diffraction (EBSD), Vickers microhardness, and miniaturized tensile testing in conjunction with digital image correlation (DIC). Finite element simulations were also conducted to obtain the local stress and strain states in the MLMs to elucidate the bulk plastic deformation behavior. The main finding was that the intermediate buffer layer, when processed with a mixture of P21 and 316L alloys, exhibited superior mechanical properties such as continuous yielding, a low yield to tensile strength, and a high work-hardening rate. The macroscopic deformation behavior was related to the initial microstructure that consisted of a small fraction of retained austenite and fine α′ martensite. During a compression test to study the bulk deformation behavior, MLMs with an intermediate buffer layer exhibited a relatively superior load-carrying capacity compared with MLMs without an intermediate buffer layer.