本研究利用有機金屬化學氣相沈積法（MOCVD）配合流體床（Fluidized Bed）技術，製備Cr2O3/Al2O3奈米複合粉體，配合高能量振動式球磨混合分散，在真空環境中以1500℃進行碳化與熱壓燒結，成功製備出高緻密性之碳化鉻/氧化鋁奈米複合陶瓷。並探討奈米複合陶瓷的相，微結構以及機械性質。

　　實驗結果發現，在流體化溫度為400℃下製備之奈米複合粉體，除了氧化鋁外，其主相為一非晶質的氧化鉻，另外，粉體中有自由基碳及介穩態之CrC1-x的存在，對日後燒結時與氧化鉻結合，相轉換為碳化鉻（Cr3C2）有很大的影響。而經由高能量振動式球磨後，複合粉體的分散性及均勻性獲得大幅的改善。

　　於真空熱壓燒結合成之Cr3C2/Al2O3奈米複合陶瓷的強度、硬度、韌性均較單質氧化鋁提升許多。微結構顯示大部分微量之奈米碳化鉻分佈在氧化鋁晶界上以及晶粒內，因而產生了強、韌化的效果。在奈米複合陶瓷的強化方面，由於奈米級第二相的引入以及鉻離子固溶到氧化鋁基地的現象產生細晶強化與固溶強化，且使得氧化鋁破壞由沿晶轉為沿晶穿晶混和的模式，其強度約可提升至475MPa；韌化方面則觀察出裂縫轉折、裂縫架橋、裂縫分支等韌化機制，其韌性約可提升至5.6MPa‧m1/2。

　　以X光測量碳化鉻/氧化鋁奈米複合陶瓷中之殘留應力，發現在添加2.2vol.％第二相之複合陶瓷中，其殘留壓應力值為-104MPa；而添加5vol.％第二相之複合陶瓷中，其殘留壓應力值為-125MPa。由於殘留壓應力的存在，藉以強化奈米複合陶瓷。

　This study using metal-organic chemical vapor deposition (MOCVD) conducted in the fluidized bed was employed for the preparation of nano-meter as-deposited powder. After high energy vibration ball milling, the composite powder was sintered by hot-press sintering at 1500℃ in vacuum and obtained the fully-densed Cr3C2/Al2O3 ceramic nanocomposites. the phases, microstructures and mechanical properties of nanocomposites were also discussed in this study.

　During the as-deposited powder preparation, The amorphous Cr2O3 deposited on the Al2O3 ceramic powder by pyrolysis of Chromium Carbonyl (Cr(CO)6) at 400℃ was used. Besides, there were also free carbon and metastable CrC1-x inside the Al2O3 and those species were helpful during the phase transformation from Cr2O3 to Cr3C2. After the high energy vibration ball milling process, we can obtain the dispersive and uniform composite powder.

　The hot-pressed Cr3C2/Al2O3 nanocomposites have better mechanical performances such as bending strength, fracture toughness and hardness than the monolithic Al2O3. The nano-sized Cr3C2 particles were mainly located within the Al2O3 grains as well as on the Al2O3 grain boundaries. The drastic change of the fracture mode from intergranular fracture of monolithic Al2O3 to transgranular fracture of nanocomposites, solid solution strengthening and grain size reduction improved the strength of Al2O3. The toughening mechanisms of the nanocomposites were crack deflection, bridging and branching.

　Moreover, we measured the residual stresses in the Cr3C2/Al2O3 nanocomposites by X-ray. The results indicated that the highly localized residual stresses in the matrix grains were generated by the mismatch of thermal expansion coefficients between the matrix and the dispersed particles. These residual compressive stresses also improved the strength and toughness in the nanocomposites.

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