本研究是利用有機金屬化學氣相沉積法(MOCVD)與流體床技術(Fluidized Bed)，製備Cr2O3/Al2O3奈米複合粉體，並配合後續的碳化處理，將奈米複合粉體變成Cr3C2/Al2O3奈米粉體後，以熱壓燒結製備出碳化鉻/氧化鋁奈米複合陶瓷。並研究奈米複合陶瓷的相、微結構以及機械性質。

實驗結果顯示，在流體化溫度為300℃所製備出的奈米複合粉體，其披覆第二相經由成分分析發現主相為一非晶質的氧化鉻外，粉體中尚有自由基碳和介穩態之CrC1-X的存在。其粉體的表面型態可分為兩類:一為粒徑較小且呈現散霧狀分布的披覆相，另一則是粒徑較大呈現島狀的披覆相。另外，氧化鉻與碳化鉻的轉換反應，深受反應物碳活性和氧分壓的影響，本實驗利用氫氣/甲烷混合氣體於800℃持溫4小時碳化氧化鉻，因低溫800℃下甲烷與氧化鉻即可反應產生碳化鉻，且藉由氫氣還原氣氛有助於碳化反應的發生，並使已反應的碳化鉻不再被氧化。

於真空熱壓1400℃持溫1小時之Cr3C2/Al2O3奈米複合陶瓷的強度、硬度與韌性均較單質氧化鋁有所提升。微結構顯示第二相粒徑大小約50~300nm不等，當中奈米第二相和團聚的第二相大多分布在氧化鋁的晶界上，和少部分第二相分布於晶粒內。機械性質中，強度因第二相碳化鉻的添加可提升至490MPa，其強化機制有晶粒細化、殘留應力、和沿晶轉沿、穿晶混合模式的破壞等強化機制，韌性方面則是提升至3.6 MPa．m1/2，其韌化機制則是裂縫偏折、裂縫分支與差排效應等韌化機制。

The metal-organic chemical vapor deposition (MOCVD) conducted in a fluidized bed has been employed for the preparation of chromium oxide/alumina nanocomposite powder. The chromium carbide (Cr3C2) / alumina (Al2O3) nanocomposite powder was successfully obtained after carbonizing the chromium oxide/alumina nanocomposite powder. The carbonized nanocomposite powder was sintered by hot-pressing at 1400℃ in vacuum. The phases, microstructures and mechanical properties of nanocomposite bulk were discussed in this study.

During the MOCVD process, the amorphous Cr2O3 was deposited on the Al2O3 powder by pyrolysis of Chromium Carbonyl (Cr(CO)6) at 300℃. Besides, there were also little free carbon and metastable CrC1-x on the Al2O3.The form of amorphous Cr2O3 can be divided into fog-like type and island-like type.

The conversion of chromium oxide to chromium carbide was closely influenced by the activity of carbon and oxygen partial pressure. The chromium oxide was carbonized with mixture gas of CH4-H2 at 800℃ for 4 hours. The hydrogen atmosphere facilitated the rate of carbonization and prevented re-oxidation of chromium carbide.

The hot-pressed Cr3C2/Al2O3 nanocomposites have better mechanical performances such as bending strength, fracture toughness and hardness than the monolithic Al2O3. The size distribution of Cr3C2 was from 50nm to 300nm. Most of Cr3C2 were mainly located on the Al2O3 grain boundary and some Cr3C2 existed within the Al2O3 grain. The fracture strength of nanocomposites increased from 375MPa to 490MPa with the mechanism of grain size reduction,residual stress and transgranular fracture. The toughness was improved from 3.0 MPa．m1/2 to 3.6 MPa．m1/2 by crack deflection、crack branching and dislocation effect.

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