Strengthening the functionally graded material of stainless steel 308L and Inconel 625 by local Nb alloying

Local Nb alloying was conducted for the unfavorable composition range of the functionally graded material (composed of stainless steel 308L and Inconel 625) fabricated by the dual-wire arc additive manufacturing. It solved the issue of weakening the solution strengthening in the range of 10 %-50 % Inconel 625, because the solution strengthening element Nb in the matrix segregated to the grain boundaries, forming secondary phases. The precipitated scattered Laves phases played a role in precipitation strengthening, but the large Laves phases, presented as chains, were unfavorable to the tensile properties. After local Nb alloying, the tensile strength increased from 385 MPa to 510 MPa, and the elongation increased from 8.3 % to 16.9 %; the fracture mode changed from ductile to mixed (cleavage and ductile) due to the hard and brittle Laves phase.

Automated summary

Local Nb alloying was conducted to address the issue of weakening solution strengthening in a functionally graded material. The addition of Nb solved this problem by preventing the formation of large Laves phases, resulting in improved tensile strength and elongation. However, the presence of chain-like Laves phases still had a negative impact on the material's tensile properties.