Characterization of Yttrium Phosphate and a Yttrium Phosphate/Yttrium Aluminate Laminate

Single‐phase yttrium phosphate (YPO₄) and a YPO₄/yttrium aluminate (Y₃Al₅O₁₂) laminate were studied. Young's modulus, Poisson's ratio, Vickers hardness, and coefficient of thermal expansion of YPO₄ sintered bodies were measured. YPO₄ and Y₃Al₅O₁₂ are chemically compatible and morphologically stable up to at least 1600°C. The fracture behaviour was studied by four‐point flexural testing on bars with ground or notched tensile surfaces, and by the indentation method. Noncatastrophic fracture could be seen in these specimens. In flexural testing, cracks could be bridged by YPO₄ layers, followed by some interfacial debonding. Indentation responses also consistently showed some interfacial delamination in the YPO₄/Y₃Al₅O₁₂ laminate.