SiC表面氧化及其对SiC/Fe界面稳定性的影响

Oxidation of SiC and Its Effect on the Interface Stability of SiC/Fe

烧结致密的α－ＳｉＣ在静态空气气氛中经１２００℃×１０ｈ氧化，在其表面形成一层致密的氧化膜，该层氧化膜具有β－方石英晶体结构．氧化膜的生长由Ｏ２通过ＳｉＯ２晶格间隙的扩散控制． ＳｉＣ／Ｆｅ界面反应剧烈，界面稳定性极差. ＳｉＣ表面氧化能有效阻挡该界面反应，提高其稳定性． ９００℃以下长时间保温，氧化 ＳｉＣ／Ｆｅ界面十分平直，无明显反应的迹象，界面十分稳定．但随着温度的升高，界面稳定性越来越低，在局部区域内开始发生反应，并逐渐扩展到整个界面，最终导致氧化膜遭到破坏，失去阻挡界面反应的作用．氧化膜与ＳｉＣ、Ｆｅ热膨胀系数不匹配所造成的应力集中，以及氧化膜中存在的孔隙可能是导致氧化膜在热处理过程中遭到破坏的主要原因．

The dense oxide layer is formed on the surface of sintered α-SiC after annealing at 1200℃ for 10h in a stationary air ambient, and its crystal structure is ofβ-cristobalite. The growth of the oxide layer is controlled by the diffusion of oxygen molecules through the interstitial site in SiO2. The solid state reaction between SiC and Fe is severe, and significantly decreases the interface stability of SiC/Fe. The oxidation of SiC has a great effect on the interface stability of SiC/Fe. At temperatures below 900℃, the interface of oxidized SiC/Fe is always smooth and remains intact after annealing for a long time. It shows that the oxide layer can hold back the interface reaction and improve the interface stability, permanently. But, the interface stability of O-SiC/Fe decreases corresponding to raising the annealing temperature. The reaction first takes place at the 'points' of the interface, and then, wholly extends along the interface. It results that the effect of the oxide layer as a reaction barrier is lost entirely. The main reasons for the oxide layer invalid after annealing at the temperature above 900℃ may be the voids existed in the oxide layer, and the stress concentration caused by the mismatch of the heat expansion coefficients between the oxide layer and SiC, Fe.