摘要
Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc ＋ bcc structures and then to bcc ＋ fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate （159.7 HV） to the top surface （545.4 HV）.
Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc ＋ bcc structures and then to bcc ＋ fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate （159.7 HV） to the top surface （545.4 HV）.
基金
financially supported by the National Key Research and Development Program of China (Grant Nos. 2016YFB1100204 and 2013ZX06002-002)
the Shenyang Science and Technology Funded Project (Grant Nos. 17-29-2-00, Y17-1-031 and Z17-2-002)
Financial support by the Youth Foundation of School of Stomatology, China Medical University (Grant No. K101593-17-05)
