Grain boundary and microstructure engineering of Inconel 690 cladding on stainless-steel 316L using electron-beam powder bed fusion additive manufacturing
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2019年第2期
论文作者：I.A.Segura L.E.Murr C.A.Terrazas D.Bermudez J.Mireles V.S.V.Injeti K.Li B.Yu R.D.K.Misra R.B.Wicker
文章页码：351 - 367
摘 要：This research explores the prospect of fabricating a face-centered cubic（fcc） Ni-base alloy cladding（Inconel 690） on an fcc Fe-base alloy（316 L stainless-steel） having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing（AM） utilizing electron-beam powder bed fusion（EPBF）. The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm2, and a homogeneous distribution of Cr23C6 precipitates. Precipitates were formed within the grains（with 3 μm interparticle spacing）,but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr23C6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle（and low energy） subgrain boundaries. In contrast, Cr23C6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.
I.A.Segura1,2，L.E.Murr1,3，C.A.Terrazas1,2，D.Bermudez1,3，J.Mireles1,2，V.S.V.Injeti3，K.Li3，B.Yu3，R.D.K.Misra3，R.B.Wicker1,2
1. W.M.Keck Center for 3D Innovation, The University of Texas at El Paso2. Department of Mechanical Engineering, The University of Texas at El Paso3. Department of Metallurgical, Materials and Biomedical Engineering, The University of Texas at El Paso
摘 要：This research explores the prospect of fabricating a face-centered cubic（fcc） Ni-base alloy cladding（Inconel 690） on an fcc Fe-base alloy（316 L stainless-steel） having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing（AM） utilizing electron-beam powder bed fusion（EPBF）. The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm2, and a homogeneous distribution of Cr23C6 precipitates. Precipitates were formed within the grains（with 3 μm interparticle spacing）,but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr23C6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle（and low energy） subgrain boundaries. In contrast, Cr23C6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.
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