Evolution of carbon nanotubes and their metallurgical reactions in Al-based composites in response to laser irradiation during selective laser melting
Evolution of carbon nanotubes and their metallurgical reactions in Al-based composites in response to laser irradiation during selective laser melting
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DOI：
10.1016/j.msea.2019.138307
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发表时间：
2019-09-23
期刊：
影响因子：
6.4
通讯作者：
Hague, Richard J. M.
中科院分区：
文献类型：
--
作者：
Aboulkhair, Nesma T.;Simonelli, Marco;Hague, Richard J. M.
碳纳米管增强的铝基复合材料因其出色的冶金和结构性能而备受青睐，这些性能在很大程度上取决于制造工艺。在这项工作中，研究了由高能球磨纯铝和多壁碳纳米管（MWCNT）制成的复合材料通过激光粉末床熔融增材制造的工艺 - 结构 - 性能关系。MWCNT（高激光吸收率）和Al（低激光吸收率）之间良好的强结合使得能量从前者转移到后者，并使热量保持更久，从而提高了熔化效率，进而改善了加工性能。在一项全面的研究中探究了MWCNT对激光照射的响应及其与Al的界面反应。X射线衍射证实，除了存在一些纳米晶石墨材料外，C部分转化为碳化铝。显微镜观察显示在熔池边界有碳化物偏析以及沿制造方向迁移的迹象。拉曼光谱表明激光照射促进了MWCNT中的再石墨化，减少了球磨引入的缺陷数量。由于Al和MWCNT之间的冶金反应形成了两种类型的Al₄C₃。它们分别是针状和六边形的Al₄C₃，并根据材料在熔化和凝固过程中经历的热分布情况解释了它们的形成机制，即直接沉淀和溶解 - 沉淀机制。大尺度电子背散射衍射表明在熔化和凝固过程中没有形成明显的织构。微纳米压痕测试显示出均匀的力学性能。
Aluminium-based composites reinforced with carbon nanotubes are widely sought for their outstanding metallurgical and structural properties that largely depend on the manufacturing route. In this work, the process-structure-property relationship for a composite made from high-energy-ball-milled pure Al and multi-walled carbon nanotubes (MWCNT) processed by laser powder-bed-fusion additive manufacturing was investigated. The strong good bond between MWCNT (high laser absorptivity) and Al (low laser absorptivity) allowed the energy transfer from the former to the latter and maintained the heat for longer allowing for better melt efficiency hence improved processability. The response of MWCNT to laser irradiation and their interfacial reactions with Al were probed in a holistic investigation. X-ray diffraction confirmed the partial transformation of C into Al-carbides in addition to the presence of some nano-crystalline graphitic materials. Microscopy revealed evidence of carbides segregation at the melt pool boundaries as well as migration along the build direction. Raman spectroscopy showed that laser irradiation promoted re-graphitisation in MWCNT, reducing the amount of defects introduced by milling. Two types of Al4C3 formed as a result of the metallurgical reaction between Al and MWCNT. These were needle-like and hexagonal Al4C3 and their mechanisms of formation, direct precipitation and dissolution-precipitation, respectively, were explained in light of the thermal profile experienced by the material during melting and solidification. Large scale electron backscatter diffraction showed that there is no distinctive texture developing during melting and solidification. Micro- and nano-indentation testing showed uniform mechanical properties.