Sp2 carbon embedded in Al-6061 and Al-7075 alloys in the form of crystalline graphene nanoribbons

Abstract

Electrocharging assisted process has been used to incorporate carbon in Aluminum 6061 and 7075 alloys ensuing significant improvements of the ultimate tensile strength, hardness, and electrical conductivity. This work investigates the presence of carbon, its structure, carbon-metal bonding, surface characterization and dispersion of carbon incorporated in Al alloys by electrocharging assisted process. Networks of Graphene nanoribbons with 3D epitaxy and preferred orientation along the <110> and <112> directions of Al are evident by transmission electron microscopy and spectrum imaging of the C-K edge electron energy loss spectra. X-ray photoelectron spectroscopy and Raman scattering corroborate sp 2 carbon in Al-6061, and hybrid sp 2-sp 3 in Al-7075 with added carbon. Kelvin probe force microscopy substantiates the presence of carbon in the Al matrix. Phonon density of states derived from first-principles calculations predicts C-Al Raman active modes whilst density functional theory indicates covalent bonding between carbon and Al. This method of incorporation of graphene nanostructures in metals with strong carbon-metal bonding can open up new avenues for incorporation of sp 2 carbon structures in other materials.

Characterization of carbon nanostructures in Al and Ag covetic alloys

“…We have previously reported the presence of carbon nanostructures like graphene nanoribbons (GNR) and graphene sheets observed in TEM [11,12]. These carbon nanostructures show primarily sp 2 C-C bonding, and weak indication of Al-C bonding was confirmed by XPS in Al covetic samples [11]. Preliminary studies by EELS corroborated mostly sp 2 bonding with small sp 3 mixtures and different stages of oxidation in these alloys.…”

“…Nevertheless, Al alloys, Cu and Ag covetics have shown superior mechanical, electrical and thermal properties [11][12][13][14]. We have previously reported the presence of carbon nanostructures like graphene nanoribbons (GNR) and graphene sheets observed in TEM [11,12]. These carbon nanostructures show primarily sp 2 C-C bonding, and weak indication of Al-C bonding was confirmed by XPS in Al covetic samples [11].…”

“…It is important to note that the actual concentration of carbon that incorporates in the lattice of the metal is lower than the nominal value. Nevertheless, Al alloys, Cu and Ag covetics have shown superior mechanical, electrical and thermal properties [11][12][13][14]. We have previously reported the presence of carbon nanostructures like graphene nanoribbons (GNR) and graphene sheets observed in TEM [11,12].…”

Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

“…354 Surface potential mapping is utilized for distinguishing carbon from the alloying elements, such as Al, Zn and Mg, as the surface potential difference is relatively small for carbon (similar work function as the tip (Pt)), as is illustrated in Fig. 16b-e. 338 In contrast, the potential difference between the metals and tip are high. 338 For example, Jaim et al utilized KPFM to analyze the difference between Al-6061 cv 3% and Al-6061 and substantiated the presence and the ribbon networks of carbon embedded in the Al-matrix of Al-6061 cv 3%.…”

“…16b-e. 338 In contrast, the potential difference between the metals and tip are high. 338 For example, Jaim et al utilized KPFM to analyze the difference between Al-6061 cv 3% and Al-6061 and substantiated the presence and the ribbon networks of carbon embedded in the Al-matrix of Al-6061 cv 3%. They observed a correlation of the dark regions in the AFM phase image (Fig.…”