本研究採用非晶氮化矽、結晶化β相氮化矽與石墨烯等奈米粉體為起始原料，利用製程參數的調整，形成單一相氮化矽的燒結體，並從中選擇適當的粉體作為起始原料，配合火花電漿燒結技術，製備石墨烯/氮化矽基奈米複合陶瓷，藉由壓痕技術探討石墨烯添加量對氮化矽機械性質的影響。
為了製備單一相氮化矽，首先利用碳熱還原處理減低非晶氮化矽粉體中的氧含量，進而抑制燒結體內氧氮化矽之第二相的生成。研究結果顯示：添加碳黑之試樣在熱處理溫度1400 0C，持溫時間10小時下，能有效與氮化矽粉體進行碳熱還原，大幅降低燒結體中氧氮化矽的含量；當碳黑添加量從3 wt%增加至5 wt%時，形成單一相氮化矽。並與不需要碳熱還原處理即能燒結出單一相的結晶化β相氮化矽粉體作燒結體機械性質的比較。
結合微結構的觀察和維氏硬度測試，評估此兩種單一相氮化矽陶瓷的機械性質。結果顯示：非晶氮化矽粉末經過碳熱處理後，部分結晶化造成起始粉末相組成的差異，傾向形成高長寬軸比的晶粒分佈在等軸狀基材中，晶粒尺寸分佈為雙峰曲線，此方法雖能製備出單一相氮化矽，但燒結試樣殘留許多的孔洞，導致機械性質的大幅下降；反之摻雜較多助燒結劑的結晶化氮化矽粉末，燒結體的孔隙率低，較小的晶粒尺寸，導致燒結體具有較高的硬度，故後續將使用結晶化氮化矽粉體作為製備石墨烯/氮化矽奈米複合陶瓷的材料設計選擇。
經由沈降實驗找出分散添加物石墨烯的最佳溶劑組合，實驗結果顯示：石墨烯在添加了2 Vol%六甲基二矽氮烷(Hexamethydislizane, HMDS)的酒精中得到最好的分散效果。此外，藉由紅外線光譜分析HMDS和氮化矽粉體間的鍵結發現，HMDS上親電子的Si能有效的在氮化矽粉體表面去除Si-OH鍵，形成粉體表面甲基化，說明此高分子可能扮演氮化矽和石墨烯粉體混合中架橋的角色。
在石墨烯/氮化矽奈米複合陶瓷的部分，添加2 wt%石墨烯於基材中，能使破裂韌性值從5.0提昇至6.3 MPa*m1/2。藉由壓痕裂縫軌跡發現，石墨烯的添加對氮化矽的韌化機制，在壓頭所造成的破壞區域產生較多的微裂縫，顯示較多破壞能在此區域的石墨烯和氮化矽界面中釋放；鑲嵌在玻璃相中各種不同排列方向的多層石墨烯，使得裂縫產生偏折和分支。此外，從裂縫內可觀察到平行和垂直試片表面的石墨烯產生的裂縫架橋，裂縫方向的改變和架橋效應使得裂縫傳播的過程中能量被分散，而提昇了氮化矽陶瓷抵抗裂縫破壞的能力。

Si3N4 is good for high-temperature applications but not widely used due to its poor toughness. The majority of our work is to investigate the toughening behavior of Si3N4/ graphene nanocomposites by controlling the phase compositions of ceramics matrix as β-Si3N4 and adding graphene as reinforcement filler. To begin with, the sinterability of nano-Si3N4 powders doped with Y2O3 (SN6Y) after performing carbothermal reduction treatment (CRT) compared to the one with Y2O3 and Al2O3 (SN6Y8A) were evaluated through microstructural characterization and Vickers hardness test. The nano-Si3N4 powders (SN6Y8A) was selected as starting powders and dispersed with 0, 1, 2, 4 wt% graphene additions. Spark plasma sintering (SPS) method was used to enable the graphene which has low thermal stability to incorporate with β-Si3N4 and limit the grain distributions to nanometer order. We found that different oriented multi-layers graphene decorating with the grain boundaries of Si3N4 results in minor cracks, cracks deflection and crack branching around the indentation contact damage zone. Further examination of the radial cracks reveals graphene bridges the cracks for both in-plane and through-thickness direction. The main toughening mechanisms are developed with minor cracks, crack deflection, crack branching and crack bridging.

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