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This work presents a fine microstructure and local misorientation study of various oxide phases in the tertiary oxide scale formed on a hot-rolled steel strip via electron back-scattering diffraction (EBSD). Local strain in individual grains of four phases, ferrite ( α -Fe), wustite (FeO), magnetite (Fe 3 O 4 ) and hematite ( α -Fe 2 O 3 ), has been systematically analysed. The results reveal that Fe 3 O 4 has a lower local strain than α -Fe 2 O 3 , in particular, on the surface and inner layers of the oxide scale. The multiphase oxides along the cracking or α -Fe 2 O 3 penetration generally develop a high local misorientation. Localised stain along the cracks demonstrates that the misorientation tends to be strong near grain boundaries. The high fraction of small Fe 3 O 4 grains accumulate at the oxide–substrate interface, which leads to a dramatic increase in the intensity of local stain. This variation is due mainly to the phase transformation among the oxide phases, i.e., the Fe 3 O 4 particles during their nucleation and growth. The combined action of stress relief and re-oxidisation is proposed to explain the formation of Fe 3 O 4 seam at the oxide–steel interface. The present study offers an intriguing insight into the deformation behaviour of the tertiary oxide scale formed on steels, and may help with understanding the stress-aided oxidation effect of metal alloys. [ABSTRACT FROM AUTHOR]

Both orientational and geometrical characteristics of grains in tertiary oxide scales have been quantitatively investigated using the electron backscatter diffraction (EBSD) technique. Phase and orientation mappings demonstrate that the {001} planes of magnetite and the {0001} planes of hematite are parallel to the direction of oxide growth. Pole figures (PFs) as scattering plots clearly display the direct correlation between the orientations and microstructure sites of magnetite grains. Magnetite grains develop a strong rotated cube texture component that shifts to the {100}< 210 > component, whereas those with the grain size of 1–5 μm develop the {001}< 100 > cube texture component. The refined magnetite grains surrounding the abnormal ones can be a combined process, including magnetite pro-eutectoid during hot rolling and cooling and re-oxidation during air-cooling. Our findings offer insights toward further understanding of the link between the geometrical and orientation parameters of grains with respect to the deformation behaviour of oxide scales formed at elevated temperatures. [ABSTRACT FROM AUTHOR]

Abstract Aluminum-graphene nanosheets (GNSs) composite was fabricated and subjected to dry sliding wear tests. A protective and lubricious tribolayer was formed between the sliding interfaces. SEM, TEM and Raman microscopies were used to characterize the cross section and top surface of the tribolayer, for the purpose of understanding the effect of GNSs on the microstructure of the tribolayer and induced tribological performance. It was found that the incorporation of 1 vol% GNSs reduced the wear and friction by 85.0% and 39.1% respectively. GNSs strengthen the formation of the protective tribolayer by wrapping sliding surface debris particles and bridging subsurface cracks. Raman mapping results indicate that the GNSs-rich tribofilms are smeared on the wear scar along the sliding direction. GNSs are self-lubricating for their ease of interlayer sliding and formation of rollers during sliding wear, which enable the reduction in friction. Graphical abstract Unlabelled Image Highlights • The incorporation of graphene in the aluminum composite contributed to reduction in wear and friction. • The dispersion of graphene in the tribolayer and the interfaces was observed. • Graphene strengthens the formation of a protective tribolayer by wrapping and bridging mechanisms. • Graphene-rich tribofilms are smeared on the wear scar along the sliding direction and suppress the friction. [ABSTRACT FROM AUTHOR]