Structural integrity and strain hardening variability of plasma metal deposited Fe-36Ni Invar alloy

The Fe-36Ni Invar alloy is known for its good combinations of strength and toughness at cryogenic temperatures. Additive manufacturing of Invar has been previously investigated predominantly using powder-bed based methods, but not via plasma metal deposition. Additionally, the strain hardening behaviour has been overlooked. Therefore, a systematic examination of the tensile behaviour as a function of the orientation and location across the 3D printed structure was performed in this study. The aim was to assess the structural integrity and strain hardening variability in plasma metal deposited Invar. It is found that local variations of the solidification conditions change both the morphology and size of the γ grains. Statistically significant variations, especially in terms of strain, were found depending on the orientation and location. This study also demonstrates that, upon loading, a structure composed of columnar grains stores lower elastic energy (i.e., modulus of resilience) when compared to cellular structures. Moreover, the plasma metal deposited Invar alloy has a favourable tensile stress (YS/UTS) ratio. • A systematic examination of the microstructural features and tensile behaviour was performed. • Local variations of the solidification conditions change both the morphology and size of the microstructural features. • Statistically significant strain variations were found depending on the orientation and location.