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<p>Joining the MEA NiCoVAl<sub>0.2</sub> to austenitic stainless steel (SS) is likely to achieve higher strength as compared to NiCoCr-based and NiCoCrMnFe MEAs resulting from higher friction stress and a high Hall-Petch coefficient of NiCoVAl<sub>0.2</sub>, which has two main challenges: one is the uncertainty of which phase forms in the fusion zone (FZ) due to a mixture of various components, and another is how to enhance the local strength of the FZ while retaining good ductility. In the present work, the microstructural features and mechanical properties of the electron-beam-welding (EBW) joint between NiCoVAl<sub>0.2</sub> and commercial grade 316 austenitic SS were assessed. A full-penetration, defect-free dissimilar joint between NiCoVAl<sub>0.2</sub> and 316 SS was fabricated by electron-beam welding. A new HEA formed within the FZ with asymmetric columnar grains. The FZ consisted of a f.c.c. matrix, a reticular B2 phase, and a few vanadium carbides. Vanadium and chromium were found to co-segregate into the interdendritic regions. The fine dendritic interspacing in the FZ, a result of the rapid cooling rate, led to a higher hardness than that of the 316 SS and the neighboring heat-affected zone. The joint showed a yield strength of 409&#xa0;MPa, an ultimate tensile strength of 741&#xa0;MPa, and a uniform strain of 17.1 pct at 298&#xa0;K, which increased to 524, 1193&#xa0;MPa, and 18.5 pct at 77&#xa0;K, respectively. At 298&#xa0;K, failure, which involved both intervoid necking and void shearing, occurred in the 316 SS because of its lower strength compared to the FZ. In contrast, at 77&#xa0;K, ductile failure occurred in the FZ without obvious necking. Plastic deformation at 77&#xa0;K was accommodated by planar slip and some mechanical twinning along with stacking fault formation. Such deformation-induced planar defects involving slip bands, intersecting slip bands, mechanical twinning, and stacking faults can enhance the strength of the FZ and delay the onset of necking instability.</p> Graphical Abstract <p></p>

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Dissimilar Electron-Beam Welding of the Medium-Entropy Alloy NiCoVAl0.2 to 316 Stainless Steel: Microstructure and Mechanical Properties

  • 期刊论文

  • 发表日期：

    2025年3月5日

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  • Hanlin Peng,
  • Ling Hu,
  • Siming Huang,
  • Ian Baker

摘要

Joining the MEA NiCoVAl0.2 to austenitic stainless steel (SS) is likely to achieve higher strength as compared to NiCoCr-based and NiCoCrMnFe MEAs resulting from higher friction stress and a high Hall-Petch coefficient of NiCoVAl0.2, which has two main challenges: one is the uncertainty of which phase forms in the fusion zone (FZ) due to a mixture of various components, and another is how to enhance the local strength of the FZ while retaining good ductility. In the present work, the microstructural features and mechanical properties of the electron-beam-welding (EBW) joint between NiCoVAl0.2 and commercial grade 316 austenitic SS were assessed. A full-penetration, defect-free dissimilar joint between NiCoVAl0.2 and 316 SS was fabricated by electron-beam welding. A new HEA formed within the FZ with asymmetric columnar grains. The FZ consisted of a f.c.c. matrix, a reticular B2 phase, and a few vanadium carbides. Vanadium and chromium were found to co-segregate into the interdendritic regions. The fine dendritic interspacing in the FZ, a result of the rapid cooling rate, led to a higher hardness than that of the 316 SS and the neighboring heat-affected zone. The joint showed a yield strength of 409 MPa, an ultimate tensile strength of 741 MPa, and a uniform strain of 17.1 pct at 298 K, which increased to 524, 1193 MPa, and 18.5 pct at 77 K, respectively. At 298 K, failure, which involved both intervoid necking and void shearing, occurred in the 316 SS because of its lower strength compared to the FZ. In contrast, at 77 K, ductile failure occurred in the FZ without obvious necking. Plastic deformation at 77 K was accommodated by planar slip and some mechanical twinning along with stacking fault formation. Such deformation-induced planar defects involving slip bands, intersecting slip bands, mechanical twinning, and stacking faults can enhance the strength of the FZ and delay the onset of necking instability.

Graphical Abstract