Surface Engineering

Hydroxyapatite (HA) coatings were synthesised on carbon/carbon composites (C/C) with a graphene oxide (GO) interlayer. The morphology and microstructure of the GO interlayer and the HA coating were researched. The effect of applying GO interlayer on the morphology and microstructure of HA coating was investigated. The in vitro bioactivity of HA coating for C/C with GO interlayer was investigated. The results indicated that the GO interlayer was spread on the surface of C/C substrate uniformly. The morphology of the HA coating on original C/C was uneven composed of HA grains with a length 10–50 μm and nanoplate structure HA grains. The morphology of the HA coating with GO interlayer was uniform composed of single nanoplate structure HA grains. The formation process of the HA coating on C/C with GO interlayer was discussed. In addition, the simulated body fluid immersion tests showed that the HA coating with GO interlayer exhibited good bioactivity.

In the present work Ni-based + 20% Cr₃C₂ composite clads were developed on SS-304 austenitic stainless steel through microwave hybrid heating technique. Experimental trials were conducted inside a domestic microwave applicator at 2.45 GHz and 900 W. The developed microwave composite clads were characterised through SEM/EDS, XRD and Vicker's micro-hardness tests. Further tribological wear behavior of the so developed clad was investigated using pin-on-disc type tribometer under dry sliding wear conditions. Microstructural analysis revealed the uniform dispersion of Cr₃C₂ particles inside the Ni matrix in the form of cellular-like structure. The presence of FeNi₃, NiSi, Cr₃Ni₂ and chromium carbide (Cr₃C₂) was confirmed from the XRD analysis, which contributes to the increase in micro-hardness of the composite clad. The average value of micro-hardness of the developed clads was found to be 450 ± 55 HV. The microwave-processed clad exhibits three times more wear resistance than SS-304 substrate.

In this study, nano-silica thin films were deposited on the surface of polypropylene (PP) non-woven fabric (NWF) by reactive magnetron sputtering with a mixture of argon and oxygen gases to improve the hydrophilicity of the materials. The effects of process parameters, including oxygen gas concentration, treatment time, and density of the sample on the resulting hydrophilicity of the fabricated product were measured in terms of relative weight increase caused by the adsorption of water and water contact angle. The results indicated that the PP NWF modified by reactive magnetron sputtering at an oxygen gas concentration of 40%, a treatment time of 20 min, and a density less than 500 g/m² showed improved hydrophilicity. In addition, the surface morphology and chemical composition of the treated samples were examined by scanning electron microscopy and X-ray photoelectron spectrometry. It was determined that the silicon dioxide nanoparticles were evenly deposited on the surface of fibres.

Dielectric barrier discharge plasma treatment was applied to modify cellulose nanofibre (CNF) surfaces with and without ultrasonic irradiation. The plasma treatment improved the wetting by deionised water and glycerol, and increased the contents of oxygen, carbonyl group, and carboxyl group on the nanofibre surface. Ultrasonic irradiation further enhanced the wetting and oxidation of the nanofibre coating. Scanning electron microscopic observations showed skeleton-like features on the plasma-treated surface, indicating preferential etching of weaker domains, such as low-molecular weight domains and amorphous phases. Ultrasonic irradiation also improved the uniformity of the treatment. Altogether, it is demonstrated that atmospheric pressure plasma treatment is a promising technique to modify the CNF surface before composite processing.

A Ni coating and nano-SiC/Ni composite coating were prepared on diamond surfaces by an electro-co-deposition method. The surface morphology of plated diamond grit and the bonding state between diamond and Fe-matrix bond were characterised by the scanning electron microscopy and energy-dispersive spectroscopy (EDS). The flexural strength and wear resistance performance of the Fe-matrix bonded diamond tool bits were tested. The results showed that the nano-SiC/Ni composite coating possesses a smoother, finer, and denser microstructure when compared with a pure Ni coating. Furthermore, the nano-SiC/Ni composite coating on diamond surfaces improved the flexural strength and wear resistance of Fe-matrix bonded diamond tool bits. The EDS analysis indicated that the chemical combination between diamond grits and Fe-matrix bonding was formed, thereby the mechanical properties of Fe-matrix bonded diamond tool bits were enhanced.

Silver/fluorocarbon (Ag/FC) nanocomposite films were successfully deposited on the polyester (PET) nonwoven using magnetron sputtering techniques with pure silver (Ag) and polytetrafluoroethylene (PTFE) targets. FT-IR, XPS, XRD and EDX were used to examine the compositions and structure of Ag and Ag/FC films. SEM and AFM were employed to observe the surface morphology. Hydrophobicity properties and electromagnetic shielding properties of the Ag- and Ag/FC-coated PET nonwoven were also investigated. The experimental results showed that the films deposited on PET nonwoven were even and dense. The Ag existed in the films was elemental silver which had high degree of crystallinity. In contrast, the FC film did not form crystalline structure containing five components, i.e. –CF₃, –CF₂–, –CF–, –C–CF– and –C–C–, C–F groups clearly observed by the FT-IR spectrum. Compared with the original PET nonwoven, hydrophobicity properties and electromagnetic shielding properties of the PET nonwoven deposited with Ag/FC nanocomposite films were improved significantly.

Platinum nanoparticles (Pt NPs) with a mean diameter of 2.7 ± 0.8 nm were successfully deposited on C₆₀ fullerene nanowhiskers (C₆₀FNWs) by coaxial arc plasma deposition (CAPD). No correlation was observed between the face-centred cubic (fcc) lattice constant and the diameter of the deposited Pt NPs, while the mean fcc lattice constant of the Pt NPs on C₆₀FNWs was less than that of bulk Pt and significantly different from that of the Pt NPs deposited on graphite particles. The Pt NPs deposited on graphite particles showed larger lattice strains than the Pt NPs deposited on C₆₀FNWs. These results suggest that the strained structure of Pt NPs deposited by CAPD changes depending on the surface energy of the carbon substrate.

The microstructure of high strength PAN-based T700 carbon fibre (C_f) with pyrolytic carbon (PyC) coating was characterised. Effects of PyC coating on the surface of carbon fibres, interface characteristics, and mechanical properties of C_f/AZ91D composites were evaluated. The results showed that the carbon fibres with PyC coating had higher surface roughness and higher graphitisation which were beneficial to ease hazardous interface reaction. C_f-PyC/AZ91D composites with an optimal PyC coating that is about 150 nm thick and has low texture exhibited ultimate tensile strength of 416 MPa, which demonstrated 35% improvement compared with the C_f/AZ91D composites. The increase of mechanical properties of C_f-PyC/AZ91D composites could be ascribed to a synergistic effect of the rough C_f surface interlocking, an optimum interfacial bonding between fibres and matrix, and protection of fibres from a corrosive attack of the aluminium element in the matrix.

This paper studied the Co–Cr₃C₂ composite coatings on the nickel-based super alloy GH4169 deposited by pulse reverse jet electrodeposition in conjunction with ultrasonic vibration. The GH4169 substrates were first annealed at 500°C for 20 min to eliminate the internal stress, and then the surface was activated chemically. The surface activation procedure and ultrasonic pulse interval time in the jet electrodeposition were investigated. The results showed that the Cr₃C₂ particle contents, microhardness, wear resistance of the coatings were significantly improved, while the surface roughness and the coefficient of friction were reduced, when the ultrasonic vibration is applied in the jet electrodeposition of the Co–Cr₃C₂ composite coatings. It is found that the intermittent ultrasonic vibration at 8 s interval time has the greatest effect on the coatings. The Cr₃C₂ particle content at this condition is at its maximum of 23.85%, with evenly particle distribution and good adhesion with the cobalt matrix. The hardness of the composite coating is 652 HV(0.5), and frictional coefficient is 0.15. It has also high thermal stability, and the microhardness can hold up to 800°C without degradation, showing a great potential for high-temperature applications.

To gain insight into bonded repairs, which are commonly applied to damaged composites, we herein investigate the effects of low-temperature plasma treatment on the surface properties of a carbon fibre/epoxy resin composite, revealing that this treatment enhances the bonding strength between the patch and damaged surface. Moreover, we probe the water contact angle, chemical composition, tensile-shear strength, and morphology of composite surfaces, showing that under optimal conditions, plasma treatment decreases the water contact angle from 78° to 35.5°, increases the surface energy by a factor of ∼2.3, and induces the formation of surface-bound oxygen-containing groups, increasing the O/C ratio by ∼70%. Compared to that of the untreated composite, the tensile-shear strength of the plasma-treated composite initially increases and subsequently decreases with increasing treatment time, with the maximum increase reaching 117%. Finally, the obtained experimental data allow the above-mentioned plasma treatment to be modelled by a four-stage process.

During the process of preparing coal tar pitch and petroleum asphalt, it is technically difficult to remove adhered asphalt through heating, chemical solvents, mechanical methods, etc. In this paper, polyphenylene sulphide/polytetrafluoroethylene (PPS/PTFE) composite coatings were fabricated on stainless steel specimens to study the adhesion of asphalt. Specimens were immersed in hot asphalt and taken out to calculate the coverage area, which was set as the standard for measuring the anti-asphalt properties. Moreover, the surfaces of the PPS/PTFE composite coatings were investigated by means of scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR) and energy-dispersive system (EDS). As the FT-IR and EDS results reveal, the PPS generated a severely oxidative reaction, and the PTFE macromolecule chain shifted gradually from the coating's interior to the surface. The PPS/40%PTFE coating exhibited the most adequate performance, which showed the best anti-asphalt behaviour, high temperature performance and strong adherence behaviours.