Liquid Mn sintering of plasma-sprayed ceramic coating

Abstract

The penetration phenomena of liquid Mn into porous Al2O3 and ZrO2 (8wt percent Y2O3) coatings, plasma-sprayed on SS400 steel substrate were studied by heating at 1573 K in a vacuum atmosphere, and the possibility of improving the mechanical properties of Al2O3 and ZrO2 coatings by heat-treatment with liquid Mn was examined. It was found that liquid Mn rapidly penetrated the ceramic coatings at the interface between the coating and the substrate. The densification of the coating occurred when Al2O3 and ZrO2 particles were sintered with liquid Mn that penetrated the porous coatings. For Al2O3 coatings, the formation of MnAl2O4 was clearly recognized in the connected porosities of Al2O3 coatings penetrated by liquid Mn. In the case of ZrO2 coatings, a dense coating was obtained by the sintering reaction between deposited ZrO2 particles and the liquid Mn. The mechanical properties, such as the hardness and the fracture stress, of both Al2O3 and ZrO2 coatings heat-treated with liquid Mn were greatly improved, compared with as-sprayed coatings. Moreover, the modules of elasticity and the fracture toughness of the ZrO2 coating reached the same levels as those of sintered Partially Stabilized Zirconia (PSZ) (Y2O3).

SS400鋼基板上にプラズマ溶射で形成した多孔質のAl2O3およびZrO2(8wt%Y2O3)中への液体Mnの浸透現象を、真空中で1573Kに加熱して研究した。そして、液体Mnを用いた熱処理による、Al2O3およびZrO2被膜の機械的性質の向上の可能性を試験した。液体Mnは、被膜と基板との界面において、セラミック被膜中に急速に浸透していくことが分かった。多孔質被膜中に液体Mnを浸透させた状態でAl2O3およびZrO2粒子を焼結すると被膜の緻密化が起こる。Al2O3被膜では、液体Mnを浸透させたAl2O3の連結多孔質体中に、MnAl2O4が形成されていくことが、はっきりと認められた。ZrO2被膜の場合は、堆積したZr02粒子と液体Mnとの間で起こる焼結反応によって緻密な膜が得られた。液体Mnと一緒に熱処理したAl2O3被膜もZrO2被膜もいずれにおいても、硬度や破壊応力など機械的性質は、溶射したままの被膜に比べて著しく向上した。さらに、ZrO2被膜の弾性係数や破壊靱性は、焼結PSZ(Y2O3)と同程度になった。