Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds

[Display omitted] •Fe2Nb phase dominant in Nb weld had an average hardness of 20.4 GPa.•Final phase constitution was modified with the composite filler (Cu20Nb).•Microstructure-mechanical properties relationship was developed by nanoindentation. In this paper, we report a thorough study of phase formation in Fe-Nb weld metals using a combination of microscopy and composition analysis. The correlation of microstructure and mechanical properties was established by nanoindentation. A simplified scenario of weld formation was proposed. Nb weld metal was dominated by the coarse Laves phase (Fe2Nb) with high hardness (∼20.4 GPa). With the addition of Cu, sound weld metal was obtained with alternative distribution of α-Fe, Cu phases and fine eutectic phases (α-Fe + Fe2Nb). These transformation products with lower hardness (α-Fe + Fe2Nb ∼ 11.6 GPa) improved the overall mechanical properties of the weld metal.