连续氮化硅纤维的氧化行为与高温影响研究

Effects of oxidative behavior on the strength and thermal resistance of continuous silicon nitride fibers

摘要:

连续氮化硅陶瓷纤维是透波／承载一体化陶瓷基复合材料的关键原材料,也是制约复合材料耐高温性能与力学性能的关键因素。本文系统研究了国防科技大学研制的连续氮化硅纤维的抗氧化性能,分析了高温处理后纤维的组成结构与力学性能变化规律。结果表明：1000°C氧化1h后纤维强度高于原始纤维强度,主要是形成的玻璃相能减少和弥补纤维的表面缺陷。随着空气中处理温度提高,氧含量增加,纤维表面形成的SiO₂层逐渐变厚,纤维强度明显降低。纤维在1200°C氧化1h后强度保留率为63%,表明在此温度以下纤维有较好的服役性能。另一方面,氮化硅纤维在1450°C N₂中处理1h的强度保留率为57%,表现出良好的耐高温性能。纤维表面氧化对其在N₂下的耐高温性能具有不利影响,1000°C氧化的纤维在1450°C处理后丧失强度,1500℃处理后形成氮化硅结晶,失重明显增长,纤维内部也开始产生缺陷。

Abstract:

This study evaluates the oxidative resistance and the thermal stability in inert atmosphere of silicon nitride fibers. When the silicon nitride fibers were oxidized at 1000 °C for 1 h, they possessed the highest tensile strength (1.53 GPa) because of the surface defect healing effect of the glassy phase, whereas those oxidized at higher temperatures showed lower strength than the non-oxidized fibers. After treatment at 1200 °C in air, they retained 63% of strength, which indicates that the fiber might possess high serving life at the temperature lower than 1200 °C. Besides, the strength retention of the fibers after 1 h at 1450 °C in nitrogen remained 57%, showing good thermal stability. However, surface oxidation adversely affected the thermal stability of the fibers at high temperatures in nitrogen because of the predominant oxygen-containing phase. Above 1500 °C, crystallization of Si₃N₄ along with decomposition of SiN_xO_y occurred, resulting in a considerable decrease in weight and a catastrophic decrease in strength for the oxidized fibers.