Preparation And Application Of Boron-doped Carbon Nanotubes In The Magnesium Matrix Composites

Carbon nanotubes (CNTs) have been considered to be a perfect reinforcement for composites due to its superior mechanical properties. Magnesium and its alloys are used as martix due to their low density, high specific strength and stiffness. The physico-chemical characteristic of the interface between CNTs and Mg matrix play a critical role in developing the CNTs reinforced Mg matrix composites with high performance. Therefore,interfacial reactions, the effects of interfaces on properties and the effective ways to control interfacial reactions are significant to Mg matrix composites with high performance.In this paper, in order to improve the interfacial bonding between CNTs and Mg matrix, boron-doped CNTs (BCNTs) were firstly prepared by calcining the mixture of B₂O₃ or B and CNTs, solid-state gas-phase boronisation. Then the CNTs and BCNTs were dispersed in Mg powder by ultrasonic and chemical method. Finally, the composites were prepared by powder metallurgy combined with hot extrusion technique.BCNTs were prepared by calcining the mixture of B₂O₃ or B and CNTs, solid-state gas-phase boronisation respectively. The impact of acidification on B-doped ratio of the CNTs was also investigated. XPS was used to validate B-doped ratio, TEM and Raman were used to analyze morphology and structure of BCNTs. The results showed that BCNTs can be successfully prepared by above methods. However, B-doped ratio was reduced by acidification of the CNTs.3-(N, N-Dimethylpalmitylammonio) propanesulfonate was used to enhance the dispersion of CNTs and BCNTs, the distribution of CNTs and BCNTs were observed by SEM, and the result indicated a better dispersion of CNTs and BCNTs in Mg powder. After obtaining composite powders, CNTs and BCNTs reinforced Mg composites were prepared by powder metallurgy combined with hot extrusion. The effects of reinforcement content and B-doping on microstructure, hardness, tensile properties, compressive properties, friction and wear properties were investigated. In addition, the interface between BCNTs and Mg were observed. The results showed that with the increase of CNTs and BCNTs content, the microhardness of the composites was increased, tensile strength and compressive strength increased firstly and then decreased, elongation decreased. The microhardness was up to 66HV when the content of CNTs in the CNTs/Mg composites is 1.5wt.%. Tensile strength and compressive strength were up to 243.4MPa and 434.8MPa when using 1.0wt.% CNTs in the composites. B-doping can improve interface between CNTs and Mg and increase strength of composites effectively. Tensile and compressive strength were 258.3MPa (+6.1%) and 473.2MPa (+8.8%) respectively for the 1.0wt.% BCNTs/Mg composites. Compressive strength of the 1.5wt.%BCNTs/Mg composites is 18.7% higher than that of the 1.5wt.%CNTs/Mg composites. The fracture observation showed that CNTs were pulled out, but BCNTs were pulled off in the fractured surface, indicating that B-doping can enhance the interfacial bonding between Mg and CNTs.