プラズマ溶射により作製したAl₂O₃/YAGコンポジットコーティングの構造制御と特性

抄録

  Nano-dispersed α-Al₂O₃/YAG composite coatings were successfully obtained by atmospheric plasma spraying (APS) of the granulated Al₂O₃/Y₂O₃ powder and the post heat treatment. The as-sprayed coating was composed of an amorphous phase, metastable Y-Al-O solid solution. After the heat treatment about 1473 K, two crystalline phases, α-Al₂O₃ and YAG, precipitated. So that the fine dispersed α-Al₂O₃/YAG composite coatings were obtained. The sizes of the precipitates could be widely controlled by time and temperature of the post heat treatment. The diameter of both particles was varied from about 10 to 150 nm, depending on the heat treatment time.
   It was found that crystallization of α-Al₂O₃ and YAG occurred during the heat treatment about 1218 K with huge volume shrinkage. Many cracks were formed in the coatings because of this volume shrinkage during the heat treatment. This affected the wear mechanism in Ball on Disk Test, and caused a fracture in the coatings heat-treated for 1-10 hr.
   Plasma pre-heating of the substrate before and during the plasma spray process was carried out, in order to keep the substrate temperature about 1423 K for in-situ crystallization. The as-sprayed coating with plasma pre-heating was composed of crystallized α-Al₂O₃ and YAG particles without any cracks. Open porosity of this coating was maintained about 2-3% even after the heat treatment at 1473 K, while the open porosity of the APS coatings increased up to 8%. Anti wear property of the coatings with plasma pre-heating were highly superior to that of the APS coatings even after the heat treatments.