High temperature corrosion of laser additively manufactured CoNiCrAlY

A Co32Ni21Cr8Al0.5Y alloy (by mass percentage) has been additively manufactured by selective laser melting (SLM). The as-deposited alloy has a γ matrix dispersing Al-rich β phase which is coarsened with time at high temperatures. The alloy grows a double-layered oxide scale consisting of outer (Co,Ni)(Cr,Al)₂O₄ and inner Al₂O₃ during 1000 h isothermal oxidation in air at 900 and 1000 ℃. The Al₂O₃ growth is dominated after a short term, particularly at the higher temperature. The growth rate of inner Al₂O₃ layer during cyclic oxidation with respect to isothermal oxidation at 1000 ℃ appears to be promoted, leading to extensive incorporation of Y-rich particles into the alumina-dominated scale. The CoNiCrAlY alloy mainly forms a major Al₂O₃ scale after 40 h during hot corrosion at 800 and 900 ℃ under Na₂SO₄+NaCl mixture. The dependence of the microstructure of the oxide scales formed on the different corrosion conditions is fully discussed.