プラズマ溶射したアルミナ皮膜のγおよびα組織〔英文〕

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Plasma sprayed coatings generally contain a high proportion of the metastable phase γ-Al_2O_3. This phase has the disadvantage that at high temperatures, above approximately 1200℃, it transforms to α-Al_2O_3 and the structure cracks because of the accompanying density increase. This study has involved determining how to prepare as-sprayed α-Al_2O_3 coatings, their mechanism of formation and a comparison of their structures with as-sprayed γ-Al_2O_3 coatings. Firstly conditions were found where coatings containing greater than 99.5% γ-Al_2O_3 could be prepared, thus ensuring that the injected powder particles, composed of particles of α-Al_2O_3, were completely melted. Then using the same conditions, the torch was traversed slowly over the substrate to produce as-sprayed α-Al_2O_3 coatings. Each pass of the torch produced structures in the coating classified as follows: Type I which contained lamellae of limited length, with lenticular-shaped pores between the lamellae and the lamellae were cracked. It is believed that the impacting particles nucleated as γ-Al_2O_3 and that solidification was complete before the next droplet arrived, but the coating transformed to α-Al_2O_3 on the heat of the torch. Type II, above Type I, where the structure was termed bandedlamellae and the particles were believed to have nucleated directly from the melt as α-Al_2O_3. Solidification was complete before the next droplet arrived to give individual lamellae. Type III, in the upper region of each pass, which consisted of long grains, over 200μm. Grains were believed to have nucleated as α-Al_2O_3 and solidification was not completed before the next droplet arrived. Thermal expansion, thermal diffusivity and pore size distributions were measured, as also were temperatures within the coatings during their deposition.
独立行政法人海上技術安全研究所の論文
1991-05-30

プラズマ溶射したアルミナ皮膜のγおよびα組織〔英文〕

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