Synthesis of carbon nanotube reinforced Al matrix composites via cold spray deposition

For fabrication of high strength carbon nanotube (CNT) reinforced Al matrix composites, the uniform dispersion, strong interface bonding and high structural integrity of CNTs have been regard as the three most important issues. In this work, two distinct approaches, namely high shear dispersion (HSD) and shift-speed ball milling (SSBM), were applied to disperse CNTs (1.5 wt.%) into pure Al powders. These two kinds of CNTs/Al composite powders as well as pure Al powders (as comparison) were deposited onto stainless steel plates under the same processing parameters. The deposition efficiency, microstructure, as well as the structural integrity of CNTs in the coatings produced from different starting powders were comparatively investigated. According to the XRD and Raman analysis, the brittle Al4C3 phase was not formed in both CNTs/Al composite coatings. Some structural damages of CNTs were found in both composite coatings, especially the one fabricated from HSD composite powder. The dispersion of CNTs onto Al particle surfaces by HSD approach did not achieve significant strengthening effect on the composite coatings, but adversely affect the metallic bonding of the particles. The microhardness of CNTs/Al composite coating produced from SSBM powders reached to similar to 115 HV0.1, showing a significant improvement compared to the pure Al coating. The strengthening mechanisms of the cold sprayed CNTs/Al composite coatings were also investigated.