Microstructure and mechanical properties of 7075 composites reinforced with TiO2-coated carbon nanotubes

Abstract

Microstructure and mechanical properties of 7075 aluminum matrix composites (AMCs) reinforced with TiO2-coated carbon nanotubes (TiO2@CNTs) prepared by high energy ultrasonic assisted casting were investigated. In this paper, a novel method was developed to increase interfacial bonding by coating TiO2 on the surface of CNTs. The results showed that high-energy ultrasound can effectively promote the uniform dispersion of TiO2@CNTs in the melt, and the TiO2@CNTs can refine the α-Al phase. The optimal addition of TiO2@CNTs was 0.9wt.%, and the optimal ultrasonic time was 10 min. The yield strength, ultimate tensile strength, and microhardness of the as-cast composites prepared under the optimal parameters were 201.22 MPa, 261.79 MPa, and 126.02 HV, respectively, which increased by 40.9%, 32%, and 32.2% compared with those of the matrix, respectively. The semi-coherent interface was formed at the TiO2/α-Al interface and well-bonded interfaces between the CNTs and the matrix were formed. The fine grain strengthening, thermal mismatch strengthening, Orowan strengthening, and direct bearing strengthening were considered as four strengthening mechanisms that occurred simultaneously, leading to excellent mechanical properties of as-cast 7075-TiO2@CNTs composites.