In situ carbon nanotube reinforcements in a plasma-sprayed aluminum oxide nanocomposite coating

Carbon nanotubes (CNT) are potential reinforcements for toughening the ceramic matrix. The critical issue of avoiding CNT agglomeration and introducing CNT-matrix anchoring has challenged many researchers to improve the mechanical properties of the CNT reinforced nanocomposite. In the current work, dispersed CNTs are grown on Al2O3 powder particles in situ by the catalytic chemical vapor deposition (CCVD) technique. Consequently, 0.5 wt.% CNT-reinforced Al2O3 particles were successfully plasma sprayed to obtain a 400 μm thick coating on the steel substrate. In situ CNTs grown on Al2O3 shows a promising enhancement in hardness and fracture toughness of the plasma-sprayed coating attributed to the existence of strong metallurgical bonding between Al2O3 particles and CNTs. In addition, CNT tentacles have imparted multi-directional reinforcement in securing the Al2O3 splats. High-resolution transmission electron microscopy shows interfacial fusion between Al2O3 and CNT and the formation of Y-junction nanotubes.