The hot corrosion resistance of 20 mol% YTaO4 stabilized tetragonal zirconia and 14 mol% Ta2O5 stabilized orthorhombic zirconia for thermal barrier coating applications

Zirconia stabilized with 3.2-4.2 mol% (6-8 wt.%) yttria (3-4YSZ), the current material of choice for thermal barrier coating applications, is susceptible to hot corrosion by acidic oxides such as vanadia in the 700-900 degreesC range. The current study is a preliminary examination of the hot corrosion resistance to NaVO3-V2O5 mixtures in the above temperature range of two alternative materials: a tetragonal zirconia co-doped with 10 mol% yttria + 10 mol% tantala (20YTaO(4)Z) and an orthorhombic zirconia doped with 14 mol% tantala (14TZ). Results show that the 20YTaO(4)SZ is resistant to destabilization by NaVO3, but is attacked at higher V2O5 activities, resulting in the formation of YVO4 and orthorhombic zirconia. Studies on the 14TZ itself then indicated that it is substantially more resistant than the YSZ to attack by environments more acidic (specifically V2O5 rich) than pure NaVO3. However, it is less suitable than either 20YTaO4SZ or 3-4YSZ for environments that are more basic. A comparison of the resistance of the 14TZ, the 3-4YSZ and the 20YTaO(4)Z shows that the 20YTaO(4)SZ is more resistant to acidic oxides than the YSZ and more resistant to the basic oxides than the 14TZ. (C) 2002 Elsevier Science B.V. All rights reserved.