Microstructure and mechanical properties of the laminated heterostructured material with 316L stainless steel/18Ni300 maraging steel fabricated by WAAM

Abstract

Heterostructured materials (HMs) have attracted extensive interest due to their excellent properties, and additive manufacturing presents great potential in fabricating HMs. A laminated HM (LHM) was prepared by wire and arc additive manufacturing with alternating deposition of 316L stainless steel (SS) and 18Ni300 maraging steel (MS). The microstructure, chemical composition, texture and mechanical properties of the LHM thin walls were investigated and compared with those of the corresponding single-material thin walls. Remelting and mixing of the previously deposited layer caused deviations in the chemical composition in both regions. The 18Ni300 MS region microstructure was composed of austenite and martensite phases with the K-S orientation relationship, and the 316L SS region microstructure consisted of the austenite phase. All samples exhibited obvious austenite phase epitaxial growth, causing grains with the same orientation to pass through multiple deposited layers. The cubic texture in the as-fabricated 316L SS sample disappeared in the 316L SS region of the LHM samples. The Goss texture intensity in the 18Ni300 MS region decreased compared with that in the 18Ni300 MS thin walls, from 20.6 to 6.36. The 18Ni300 MS region microhardness of the LHM samples of 263 HV was lower than that of the 18Ni300 MS sample due to the lower-hardness austenite phase. The ultimate tensile strength of the LHM samples was 635.25 ± 31.1 MPa, which was between those of 316L SS and 18Ni300 MS. The uniform and total elongations of the LHM samples were 19.85 ± 3.6% and 29.2 ± 2.3%, which were higher than the mixing law-calculated values. The plasticity improvement was attributed to transformation-induced plasticity and stress state variation. In the initial plastic deformation stage, the 18Ni300 MS region underwent more plastic strain with a high dislocation density, causing the strain-induced martensitic transformation. The 316L SS region was strengthened with high strain, and its necking caused stress state conversion from uniaxial to multiaxial stress.