Study On The Dealloying Of NiMn Alloy

Commercially available Ni（99.9%） and Mn（99.9%） were melted together byelectromagnetic induction under Ar atmosphere to prepare precursor Ni-Mn alloy.Subsequently, the alloy ingots were annealed at1173K for48h, quenched in water. Finally,Ni₂₀Mn₈₀, Ni25n75, Ni₃₀Mn₇₀, Ni₅₅Mn₄₅were obtained. Commercially available Ni（99.9%） andZn（99.9%） were melted together by the same method to produce Ni-Zn alloy, furnace cooling.And a Ni25Zn75alloy was obtained.The electrochemistry characteristics of Ni-Mn alloy in aqueous H₂SO₄and （NH₄）₂SO₄were studied. The results show that, the critical potential increases with increasing content ofnickel. Particularly, The anodic polarization curves of Ni₅₅Mn₄₅in aqueous （NH₄）₂SO₄hassignificant “passivation-like” region.The dealloying of Ni₂₀Mn₈₀, Ni₂₅Mn₇₅, Ni₃₀Mn₇₀alloys in aqueous H₂SO₄and（NH₄）₂SO₄under free corrosion conditions or constant potential corrosion conditions, did notform nanoporous structure. There are numerous crackles on the specimen surface, bricks like.EDXS indicated about10at.%of residual Mn. After the dealloying of Ni₅₅Mn₄₅in aqueous（NH₄）₂SO₄under constant potential corrosion conditions, small porous structure was obtainedwith pore size about100nm. EDXS indicated almost40at.%of residual Mn. The porousstructure became coursing with increasing corrosion potential. Ni₅₅Mn₄₅dealloyed in aqueous0.1M H₂SO₄under free corrosion for certain time, will also get porous-like structure.