論文摘要

氮化矽基陶瓷是目前被廣泛應用的結構陶瓷材料之一，其優異的性質包括質輕、高硬度、高強度、耐高溫、耐熱震及耐蝕性；且在高溫環境下，仍能保有極佳的強度、破壞韌性及耐熱衝擊性。由於奈米風潮的興起，近年來也有人在氮化矽陶瓷中添加奈米碳化矽作為強化第二相，期能強化氮化矽陶瓷之機械性質。

本研究主要分為二部分，第一部份探討奈米級碳化矽在氮化矽中之分散，第二部份探討添加不同含量奈米級碳化矽之影響。實驗中以不同含量的奈米級碳化矽粉末(50 nm)分散於氮化矽基材中，利用適當的溶劑與分散劑及配合行星式高能量球磨機，有效分散碳化矽於基地中；並利用熱壓燒結製備SiC/Si3N4奈米複合材料，進而研究其機械性質。以X光繞射儀進行燒結體晶相分析，利用掃瞄式(SEM)與穿透式(TEM)電子顯微鏡觀察燒結體之微結構變化，並觀察奈米級碳化矽之分散情形。

研究結果顯示，以乙醇作為碳化矽與氮化矽陶瓷粉之溶劑，並添加聚乙烯亞胺(PEI)為分散劑，能得到最佳的分散效果。而熱壓燒結後的燒結體，以穿透式電子顯微鏡（TEM）觀察發現，奈米碳化矽平均的粒徑均小於100 nm，主要分散在氮化矽晶粒間與晶界上。以SEM顯微結構照片以及影像分析儀之數據判斷，氮化矽的晶粒將隨著碳化矽添加量增加而出現降低的趨勢；由視長寬軸比（aspect ratio）比較，添加微量（5、10 wt %）的碳化矽能有效抑制氮化矽長柱狀晶粒的成長。當添加量增多時，抑制的現象並不明顯。由高解析度穿透式電子顯微鏡觀察碳化矽與氮化矽之間的界面關係，發現界面間存在因錯接合（mismatch）而引起的刃差排（edge dislocation）。

添加不同含量奈米級碳化矽對氮化矽機械性質之影響的結果顯示，添加5 wt%碳化矽/氮化矽熱壓燒結體能得到最佳的破壞強度值，但隨著碳化矽添加量的增加，燒結體破壞強度有逐漸降低的趨勢。其原因為添加少量的碳化矽能有效抑制晶粒成長，所以破壞強度較高。

添加5 wt%碳化矽/氮化矽熱壓燒結體同樣能得到最佳硬度值，整體晶粒較小是主要原因。而隨著碳化矽添加量的增加，燒結體硬度值卻逐漸降低，這是因為燒結體表面微孔隨著碳化矽的增加而增多，而導致硬度下降的趨勢。添加5 wt%碳化矽/氮化矽熱壓燒結體略比單質的氮化矽破壞韌性為高。而隨著碳化矽添加量的增多，燒結體破壞韌性呈現下降的趨勢。

在燒結體的破壞行為中，無法判別奈米級碳化矽對氮化矽所造成的影響，但是由裂縫成長與破斷面之觀察仍可看到燒結體的韌化行為，主要以裂縫轉折、晶粒架橋、晶粒拔出等行為強化材料韌性。

Abstract

Industry application of silicon nitride ceramics is hindered because of its softening at high temperature and also its brittleness . In order to overcome the problems , one of the ways suggested some years ago is to prepare SiC-nanoparticle-reinforced Si3N4-matrix composites . This thesis reports the results of processing of SiC(n.p) / Si3N4 composites and characterization of the composites .

SiC(n.p) /Si3N4 composites were fabricated by hot pressing at 1850℃ for 1 h in N2 atmosphere with Al2O3 and Yb2O3 as sintering additives . The optimum experimental procedure for manufacturing nanocomposites investigated by sedimentation test , planet ball milling test and different drying methods test .

TEM observation showed that the SiC particles located within Si3N4 grain and on the grain boundary . While SiC particles dispersed in grain boundary are bonded to Si3N4 grain without glassy phase .

The influence of SiC fine particle dispersion on microstructure and mechanical properties of Si3N4 ceramics has been investigated .The mean size and the aspect ratio of the obtained β- Si3N4 grains decreased as a result of the SiC dispersion , thus bringing about increased flexural strength and decreased fracture toughness .

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