Heat treatment of plasma-sprayed Al2O3 and Al2O3-WO3 coatings between 500 and 1000 °C

► The heat treated Al2O3 coating transformed from γ-Al2O3 to δ/θ-Al2O3. ► Heat treatment of the Al2O3-WO3 composite at 500 °C generated surface features of WO3. ► At 700 °C the surface WO3 phase reacted with Al2O3 to form Al2(WO4)3 on the surface. ► At 900 °C the surface WO3 phase vaporised before reacting with Al2O3. ► The greatest loss of W from the composite occurred at 1000 °C.