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: 材料科学技术（英文版）
• 年，卷（期）: 2019,（2）
• 页码范围: 351-367
• 页数: 17页
• 语种: 英文

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 cm-2,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 Inconel690 cladding and the 316 L stainless-steel substrate at 685 ℃ for 50 h precipitated Cr23C6 carbides in the Inconel690 columnar grain boundaries,but not in the low-angle (and low energy) subgrain boundaries.In contrast,Cr23 C6 carbides precipitated in the 316 L stainless-steel grain boundaries,but not in the low energy coherent {111 } twin boundaries.Consequently,the Inconel 690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.