Dependence of Dissolution Rate of Inconel Alloy 600 with Coarse Columnar Crystals on Crystallographic Orientation in Potentiostatic Etching

Abstract

The effect of surface orientation on dissolution rate of Alloy 600 with coarse columnar crystals was investigated by potentiostatic etching in the active region in H₂SO₄-NH₄SCN and H₂SO₄-NaCl solutions. {100}∼{110} planes and {110}∼{111} planes were prepared by cutting at 90° and 45° to ⟨100⟩ growth direction of the columnar crystals. Flat surfaces were formed on grains after etching. As the depth of dissolution from the initial surface increased linearly with the etching time, the dissolution rate was treated as constant on every grain. The dissolution rate also changed with the etching potentials and solutions. The orders of the dissolution rate on the {hkl} surface, V_⟨hkl⟩, were as follows: V_⟨100⟩<V_⟨110⟩\fallingdotseqV_⟨111⟩ at −0.1 V (vs. SCE), V_⟨100⟩<V_⟨111⟩<V_⟨110⟩ at +0.1 V in 0.5 kmol·m⁻³-H₂SO₄+2.5 mol·m⁻³-NH₄SCN solution and V_⟨111⟩\fallingdotseqV_⟨100⟩<V_⟨110⟩ at 0 V in 2.5 kmol·m⁻³-H₂SO₄+0.5 kmol·m⁻³-NaCl solution. Residual planes in each condition were determined from these dissolution rate ratios.