Hot corrosion of cobalt chromium aluminum yttrium alloys.

摘要

The kinetics and mechanisms of the hot corrosion of CoCrAlY alloys over wide ranges of temperature (600-1000{dollar}spcirc{dollar}C) and Pso{dollar}sb3{dollar} (10{dollar}sp{lcub}-6{rcub}{dollar}-10{dollar}sp{lcub}-3{rcub}{dollar} atm) were studied. Isothermal and cyclic experiments were performed to study the kinetics, and microstructures were examined by scanning electron microscopy. After interpreting these results, the hot corrosion mechanisms of the CoCrAlY alloys were proposed to explain the observed behavior.; The reaction mechanism governing hot corrosion is thought to be as follows. At low temperature (600-800{dollar}spcirc{dollar}C), SO{dollar}sb3{dollar} and CoO react and form a molten Na{dollar}sb2{dollar}SO{dollar}sb4{dollar}-CoSO{dollar}sb4{dollar} salt mixture. Aluminum diffuses through the alloy, is oxidized, and the alumina which is formed becomes subject to basic fluxing. While alumina is subject to the Rapp-Goto mechanism, chromia may not be subject to this mechanism. Since Co is left behind in the alloy, the basic fluxing of alumina seems to be the cause for formation of nonprotective scales. Sulfides can form during low temperature hot corrosion and considerable sulfide formation is observed at 800-850{dollar}spcirc{dollar}C, but the sulfidation process is less likely to be the major cause of LTHC. Also, the sulfite formation mechanism is evaluated, and the activity of aluminum sulfite is found to be too low for this compound to exist. At high temperature (900-1000{dollar}spcirc{dollar}C), the CoCrAlY alloy was in the initiation stage due to the formation of protective alumina during isothermal tests.; The mode of degradation of the CoCrAlY alloy at 1000{dollar}spcirc{dollar}C in pure oxygen during the cyclic tests was basic fluxing of alumina and chromia accompanied by spalling and cracking of oxides.