氧化鋯含量對碳化矽/氧化鋁/氧化鋯複合材料高溫氧化行為的影響

Abstract

本研究是以熱壓法製備碳化矽體積比為30% 的複合材料，基地為不同體積比的氧化鋯與氧化矽，以AZxx表之，其中xx代表氧化鋯在基地中的體積百分比；複合材料則以 AZxx/SiC符號表示。試片在1000℃~1350℃間進行氧化，然後以光學顯微鏡(OM)、X光繞射儀(X-ray)、掃描式電子顯微鏡(SEM/EDS)、穿透式電子顯微鏡(TEM/EDS)鑑定氧化層的顯微結構。實驗結果顯示氧化試片的weight gain隨氧化鋯含量的增加而增加，這是由於氧化鋯的添加促使氧在基地相的擴散速率增加所致，當氧化鋯的體積百分比超過某個臨界值時，氧化速率會迅速增加呈現明顯不同的氧化行為。AZ0/SiC與AZ10/SiC具有較淺的氧化深度及較陡的氧化層厚度變化梯度，氧化行為屬於Mode I； AZ20/SiC與AZ50/SiC具有較深的氧化深度及較平緩的氧化層厚度變化梯度，氧化行為則是屬於Mode II。AZ10/SiC、AZ20/SiC、AZ50/SiC經1200℃氧化生成cristobalite與zircon，未有mullite的生成。AZ0/SiC經1350℃/200hr氧化，氧化矽與氧化鋁作用，固溶再析出生成新的結晶相mullite。AZ10/SiC、AZ20/SiC在1350℃氧化初期，氧化矽分別與氧化鋯和氧化鋁作用生成zircon與mullite， zircon在經長時間氧化後會與氧化鋁作用生成氧化鋯及mullite。而AZ50/SiC經1350℃氧化，氧化矽擴散入基地相，且優先與氧化鋯作用生成zircon。

The composites contented 30 vol% SiC was fabricated by hot pressing. It wilth different volume percent of zirconia and alumina in matrix, expressed as AZxx (xx meaned the percentage of zirconia in matrix). The composites represented as AZxx/SiC. Composites were exposed in air at 1000℃~1350℃，and the microstructures of the oxidized samples of various composites after exposured at a temperature of 1350℃, were studied using X-ray diffraction, SEM, TEM, and energy-dispersive spectroscopy ( EDS ). The result showed the oxidation weight gain increase with the raise of zirconia content. Because of the raise of zircon content caused the increase of diffusion rate. The oxidation rate was dramatically increased beyond the critical volume fraction, and displayed a different oxidation behavior. AZ0/SiC and AZ10/SiC were characterized by a small oxidation depth as well as a relatively large gradient, which exhibited oxidation behavior of Mode I. AZ20/SiC and AZ50/SiC were characterized by a large oxidation depth as well as a relatively small gradient demonstrated the oxidation behavior of Mode II. AZ0/SiC、AZ10/SiC、AZ20/SiC formed cristobalite and zircon, but without mullite under the oxidation of 1200℃. The solution and reprecipitation between silica and alumina resulted in a newly phase mullite after AZ0/SiC exposured in air at the temperature of 1350℃ for 200h. AZ10/SiC and AZ20/SiC formed zircon and mullite at the first stage of oxidation at the temperature 1350℃, resulted from the reaction between silica and zirconia, silica and alumina. After a long term oxidation, zircon reacted with alumina and produced zirconia and mullite. AZ50/SiC exposured at 1350℃ prefer to formed zirconia through the reaction between silica and zirconia.