Unraveling the dispersion mechanism of carbon nanotubes in aluminum powder particles during high energy ball milling by FIB-TEM study

For the development of high-performance aluminum (Al) matrix composites reinforced with carbon nanotubes (CNTs), high energy ball milling (HEBM) is the most prevalent method to disperse CNTs in Al powder. However, the dispersion mechanism of CNTs in Al powder is still unclear, mainly because it is difficult to characterize CNTs when they are buried inside Al powder particles. Herein, focused-ion-beam-assisted transmission electron microscopy observation of CNTs in Al powder via HEBM with various milling times was conducted. Results showed that with increasing HEBM time, CNTs clusters were firstly broken up to be dispersed shorter-lengthed CNTs on the surface of Al flakes with gradually reduced thickness. Afterward, cold-welding of Al flakes was the predominant phenomenon, which resulted in re-spheroidization of Al powders and homogeneously dispersed CNTs. This study may provide guidance for controlling and optimizing the HEBM process to disperse CNTs in Al matrix towards the development of high-performance CNTs/Al composites.