Nonstoichiometry and realistic layered CMAS corrosion routes in Gd2-xZr2+xO7+x/2

Gd 2-x Zr 2+x O 7+x/2 ceramics were used to determine how nonstoichiometry in ceramic phases governs CMAS corrosion. All compositions retained a fluorite average structure, but Raman spectroscopy, sintering behaviour and grain growth revealed composition-dependent non-stoichiometry-driven disorder before CMAS contact. During heating, characteristic CMAS spreading temperatures depended only slightly on nonstoichiometric composition, whereas spreading rate and final spreading extent vary markedly with nonstoichiometry. After exposure at 1300 °C, all samples developed a dense inner layer and a fully reacted layer, following approximately linear and square-root time dependences of layer thicknesses, respectively. All nonstoichiometric ceramic compositions outperformed the stoichiometric composition, but the mechanistic origins of these effects were distinctly different depending on the type of nonstoichiometry, defined by different reaction products and layer-specific chemical partitioning. CMAS resistance is therefore strongly influenced by how nonstoichiometry directs competition between corrosion layers.