Lass Eric A, Stoudt Mark R, Williams Maureen E, Katz Michael B, Levine Lyle E, Phan Thien Q, Gnaeupel-Herold Thomas H, Ng Daniel S
Materials Science and Engineering Division Material Measurement Laboratory, Gaithersburg, MD, USA 20899.
Intelligent Systems Division Engineering Laboratory,Gaithersburg, MD, USA 20899.
Metall Mater Trans A Phys Metall Mater Sci. 2017;48(11). doi: 10.1007/s11661-017-4304-6.
The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 h at 1143 K (870 °C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0 NiNb δ-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials' performance in service. The δ-phase platelets are found to precipitate within the inter-dendritic regions of the as-built solidification microstructure. These regions are enriched in solute elements, particularly Nb and Mo, due to the micro-segregation that occurs during solidification. The precipitation of δ-phase at 1073 K (800 °C) is found to require up to 4 h. This indicates a potential alternative stress-relief processing window that mitigates δ-phase formation in this alloy. Ultimately, a homogenization heat treatment is recommended for additively manufactured Inconel 625 because the increased susceptibility to δ-phase precipitation increases the possibility for significant degradation of materials properties in service.
研究了激光粉末床增材制造的Inconel 625在1143 K（870°C）下进行1小时的焊后应力消除退火过程中的微观结构演变。结果发现，这种行业推荐的热处理促进了大量正交D0 NiNb δ相的形成。已知该相在传统锻造的Inconel 625中对断裂韧性、延展性和其他力学性能有有害影响；并且通常被认为对材料在服役中的性能有害。发现δ相薄片在增材制造后的凝固微观结构的枝晶间区域内析出。由于凝固过程中发生的微观偏析，这些区域富含溶质元素，特别是Nb和Mo。发现在1073 K（800°C）下δ相的析出需要长达4小时。这表明存在一个潜在的替代应力消除处理窗口，可以减轻该合金中δ相的形成。最终，建议对增材制造的Inconel 625进行均匀化热处理，因为对δ相析出的敏感性增加会增加材料在服役中性能显著下降的可能性。
