Laser-cladding and interface evolutions of inconel 625 alloy on low alloy steel substrate upon heat and chemical treatments

Abstract

Dual-layer structures of inconel 625 (In625) alloy have been deposited by laser-cladding on low alloy steel substrates for corrosion protections at elevated temperatures. Structural and morphological characterizations, before and after treatments in molten salts and/or acidic solutions, reveal absence of corrosions of the In625 layer except for a ~ 2-μm-thick Cr2O3 layer formed on its surface. However, the heat treatments give rise to remarkable δ-Ni3Nb precipitations along with an in-plane lattice shrinkage [i.e., εγ(111) = −0.26%] of the In625 layer; the former are replaced by carbides (i.e., M3C/M23C6) while the latter is increased to εγ(111) = −0.66% when approaching the In625/MS interface. Chemical treatments reveal a much faster material removal from the heat affected zone (HAZ), RHAZ, than those from the base material of the substrate, RS. They also reveal an in-plane lattice expansion [i.e., εγ(111) = 0.31%] of the In625 layer near the interface along with the material removal. In comparison, after the heat treatment, RHAZ became smaller than RS and, meanwhile, the shrunken in-plane lattices do not exhibit any expansions upon the chemical etching. These observations provide evidence that both the carbide precipitations and the local strains play an important role in the interface stability of the laser-cladded In625/Steel structures upon heat and/or chemical corrosions.