Systematic Study on the Role of Mn, Si, and Fe on the Corrosion Resistance of Ni-Based Superalloys Exposed to Air, Gaseous Sulfur Oxides and Salts

Abstract This work investigates the effect of alloying elements Mn, Si, and Fe on the corrosion resistance of polycrystalline Ni-based superalloys, at $$700\,^{\circ }{\hbox {C}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>700</mml:mn> <mml:mmultiscripts> <mml:mspace/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> in air and 300 vpm $${\hbox {SO}}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>SO</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> under 5 $${\mu {\hbox {g}}}\,{{\textrm{cm}}^{2}\,h}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mrow> <mml:mi>μ</mml:mi> <mml:mtext>g</mml:mtext> </mml:mrow> <mml:mspace/> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>cm</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> <mml:mspace/> <mml:mi>h</mml:mi> </mml:mrow> </mml:mrow> </mml:math> salt coating. Oxide scale morphology and composition was investigated using SEM–EDX and APT, revealing Mn–Fe-enriched $${\hbox {Co}}_{3}{\hbox {O}}_{4}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>Co</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mtext>O</mml:mtext> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> particles in the upper outward growing scale as well as Si-Fe-enriched clusters in NiO. Along the NiO– $$ {\hbox {Co}}_{3}{\hbox {O}}_{4} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>Co</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mtext>O</mml:mtext> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> phase boundary, a tight network of Fe-decorated dislocations relieving stress between the lattices was identified through APT. In the inward growing scale, Si enrichment was observed in the form of oxides and sulfides, while no Mn was detected. Graphical Abstract