- 學位論文
不同直徑奈米碳管強化鋁基複合材料拉伸及磨耗性質之研究
Tensile and Wear Property of Various Diameter Carbon Nanotubes Reinforced Aluminum Composites
摘要
本研究主要針對粉末冶金製程6061鋁合金及鋁基複合材料，探討添加不同直徑的奈米碳管對機械強度及磨耗性質的影響。實驗材料為6061鋁合金及6061鋁合金添加1wt%不同直徑的奈米碳管，實驗內容可分為四部份：一是製作鋁基複合材料的前處理；二是製程部份；三是室溫拉伸試驗；四是磨耗性質測試。 (一) 前處理部份：鋁合金經由脫蠟處理可將潤滑劑由1.1wt%降至0.045wt%。奈米碳管和鋁合金分別經由48小時的球磨，可打散奈米碳管之間的團聚並將長度減至5μm以下；鋁合金粒徑可由74μm減至29μm。 (二) 製程部份：將奈米碳管與鋁粉以濕式混粉後，再經由冷均壓成形、在氮氣下進行液相燒結。奈米碳管和鋁合金經球磨步驟之後再以濕式混粉的方式可改散奈米粉末團聚現象，之後進行熱擠型可得到理論密度接近100%材料。 (三) 室溫拉伸：拉伸強度以添加1wt%、直徑10~20nm經球磨過後的奈米碳管鋁基複合材料的性質最佳，因為奈米碳管經球磨過後可改善團聚現象，而未經球磨過的鋁基複合材料會在拉伸破斷面上的漩渦狀內發現奈米碳管的團聚，造成拉伸強度的下降。 (四) 磨耗性質：磨耗速率以添加1wt%、直徑10~20nm經球磨過後的奈米碳管鋁基複合材料為最低。而磨耗速率快慢與時效硬度有所關係，以尖峰時效的磨耗速率為最低，這與時效過程中析出物大小、析出物與鋁合金的界面形態有關。隨著奈米碳管的直徑增加，磨耗速率隨之增加，甚至高於未添加強化相的鋁合金，這與奈米碳管的結構有關，造成奈米碳管無法傳遞應力至基材中，形成應力集中。
並列摘要
The essential purpose of this research is to investigate the effects of diameters of carbon nanotubes on the mechanical and the wear properties of Metal Matrix Composites (MMCs). 6061 Al alloy powder (74μm) is used as metal matrix, and 1 wt% of carbon nanotubes with various diameters are added as strengthen phase. All MMC samples are prepared by powder metallurgy. The hydrocarbon content in the Al alloy is decreased from 1.1 wt% to 0.045 wt% through de-waxing. After 48 hours of planetary ball milling, the length of carbon nanotubes is cut down to less than 5 μm, and the particle size of Al alloy powder decreased from 74μm to 29μm, respectively. Wet mixing of the Al alloy powder and carbon nanotubes is adopted to avoid agglomeration of carbon nanotubes. After cold isotropic pressing, sintering and hot extrusion, composites with a density close to 100% of the theoretical density is obtained. MMCs with the addition of 1wt% ball-milled carbon nanotubes of diameters 10~20nm is observed to have the largest tensile strength due to good dispersion of carbon nanotubes in the metal matrix. Those contain carbon nanotubes without ball milling have lower tensile strength, the fracture surface is observed to take place around inclusions. Large amount of carbon nanotubes were found in the fracture surface, suggesting that the agglomeration of carbon nanotubes provided sites for crack initiation. The addition of 1wt% ball-milled carbon nanotubes of diameters 10~20nm gives MMCs the lowest wear rate. The wear rate is influenced by the aging condition. Lowest wear rate is obtained at the peak aged condition. This is in relation to the size of the precipitates during aging as well as the morphology of the interface between the precipitates and the Al alloy. As the diameter of carbon nanotubes increases, wear rates also increases, even higher than the Al alloy. This is related to the structures of the carbon nanotubes. Non-uniform axial deformations inside the multiwalled nanotubes may exist.
參考文獻
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