Investigation of a new type of composite ceramics for thermal barrier coatings

In order to explore a novel material for thermal barrier coatings (TBCs), the composite ceramic materials of lanthanum zirconate (La₂Zr₂O₇) and lanthanum phosphate (LaPO₄) were prepared by calcining. The phases and micro-structures of La₂Zr₂O₇/LaPO₄ composite ceramic materials were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The properties of La₂Zr₂O₇/LaPO₄ material, such as thermal conductivity, coefficient of thermal expansion (CTE) and mechanical properties of La₂Zr₂O₇/LaPO₄ were investigated using laser flash method, high-temperature dilatometer and micro-hardness test. Based on XRD patterns, the pyrochlore and monazite phases were obtained in La₂Zr₂O₇/LaPO₄ composite ceramic material without any chemical reaction. According to SEM morphology, the La₂Zr₂O₇ was closely near to LaPO₄ along with a lot of pores, it might cause the decrease of thermal conductivity. The thermal conductivities of composite ceramics were similar to that of La₂Zr₂O₇. The CTE of them were about 10 × 10^− 6 K^− 1, which was close to the value of LaPO₄. Because of doping LaPO₄, hardness and Young's modulus of samples were lower than that of La₂Zr₂O₇. The studies revealed that the La₂Zr₂O₇/LaPO₄ composite ceramics had good mechanical and thermal physical properties and could be applied as new candidate materials for TBCs in the future.