Phase composition and properties of plasma-sprayed zirconia thermal barrier coatings

The use of X-ray diffraction combined with TEM analysis has been used to study the crystalline structure and change in phase composition of zirconia coatings containing 6–12 wt% Y₂O₃. The optimum composition for maximum durability, observed for coatings within this composition range, is believed to be related to the microstructure developed on rapid cooling and to the volume fractions of t′, c and m phases formed during the evolution of the coating. The amount of these phases present in commercial thermal barrier coatings has been determined using X-ray diffraction and the mechanisms of toughening deduced from TEM examination of the sections of the coatings. The results obtained are discussed in relation to the degree of toughness and hence the thermal shock resistance which is a major factor in determining service life.