Surface Review and Letters

In this paper, we summarize research progress on the design and preparation of organic–inorganic hybrid coating molecular networks, which are based on the basic theory of organic–inorganic hybrid network construction. Among them, we focus on expounding the essential problems of hydrolysis during sol preparation particularly. In addition, the status of research related to titanium-containing organic–inorganic hybrid protective coatings for the surfaces of lightweight alloys such as steel, aluminum and magnesium is introduced here.

This paper represents the nanomechanical properties of various loading levels of montmorillonite clay filled polyester composites and randomly distributed jute fiber reinforced hybrid composites through Vickers micro-hardness test. The study of indentation fracture mechanics in polymer materials is a simple and cost-effective technique for the determination of fracture toughness. Ultrasonication technique was used to disperse the clay in the polyester matrix. The hand layup method was adapted to prepare the test specimens. Incorporation of 5wt.% montmorillonite clay into the polymer matrix results in an enhancement in hardness of 26.52% and the modulus of elasticity increased from 4205.21MPa for neat polyester to 5051.46MPa with the addition of clay. Fracture toughness was observed to depend on the montmorillonite clay content, and the maximum value was observed at 5wt.% nanoclay and 25wt.% jute fibers. The results show that the increase in the fiber content reduces the crack propagation in hybrid composites and increases the fracture toughness. To predict the crack size, the scanning electron microscope images are used.

In this study, the diamond films are deposited on tungsten carbide substrates with 10wt.% Co via hot filament chemical vapor deposition (HFCVD). Amorphous SiC (a-SiC) interlayers with various thicknesses are fabricated between the diamond films and tungsten carbide substrates via precursor pyrolysis to promote the adhesion and friction performance of diamond films. Indentation tests are performed to evaluate the adhesion of the as-fabricated diamond films, which show that the a-SiC interlayers can greatly improve the adhesive strength between diamond films and tungsten carbide substrates with 10wt.% Co. Moreover, the thickness of a-SiC interlayer is of great importance for the effectiveness on the film–substrate adhesion enhancement. The optimum thickness of a-SiC interlayer is 1$\mu$m. Afterwards, ball-on-disc experiments are chosen to check the tribological properties of the as-fabricated a-SiC interlayered diamond film specimen with the optimum interlayer thickness, which exhibits lower friction coefficient than the conventional diamond film with no interlayer.

The present research paperfocusses on manufacture of AlSi₆Cu₄–3 wt.% TiO₂ metal matrix composite (MMC) through liquid metallurgy route, and the manufactured composites are tested for their dry sliding wear behavior using response surface methodology (RSM). The extensive microstructural investigation is carried out to examine the dispersion of Titania particles, its bonding ability, and embedment characteristics with the matrix. The wear rate on the developed MMC is investigated and predicted using regression model. Further, the confirmation test is conducted to validate the model. The microstructures of the composite had revealed that TiO₂ particles are dispersed in the Al matrix. Further, the surface plots show that the wear rate started to vary linearly with the function of load whereas the wear rate starts to vary nonlinearly with the function of the sliding velocity and the sliding distance. In addition, the worn surfaces were investigated through the scanning electron microscopewhich addressed the wear mechanisms and revealed that TiO₂ particles enhance the wear performance of aluminum alloy by a reduction in material removal at all wear conditions.

We report the effect of potassium cyanide etching treatment on structural, optical and electrical properties of Cu₂ZnSnS₄ thin films prepared by a spray-assisted chemical vapor deposition process. Raman spectroscopy and X-ray diffraction measurements before and after potassium cyanide etching have confirmed the kesterite structure of Cu₂ZnSnS₄ films. Potassium cyanide treatment led to the elimination of ${\text{Cu}}_{2-x}$S secondary phase. Optical measurements showed that the band gap value was about 1.52eV. The best electrical resistivity and Hall mobility values were reached for a deposition temperature of 450^∘C in both cases without and with potassium cyanide treatment.

Polyvinyl alcohol (PVA) films doped with potassium iodide (KI) have been prepared by casting from their aqueous solutions. The structure of the doped samples was investigated using Fourier transform infrared spectroscopy. The addition of KI to PVA structure leads to form crosslinking as well as the increase of the amorphous ratio within the investigated sample. The optical measurements were recorded at room temperature in the range of 200–2500nm. It was found that the optical energy gap of the investigated sample increases with increasing KI ratio. The effect of the addition increment of KI on the optical parameters of PVA has been investigated. Dielectric spectra of PVA doped with KI were studied in the temperature and the frequency ranges of 303–373K and 100Hz–5MHz, respectively. The behavior of dielectric constant (${\epsilon }_1$) and dielectric loss index (${\epsilon }_2$) of PVA sample doped with KI exhibits good linearity with temperature. The obtained results suggest strongly the applicability of these materials in the temperature sensor applications.

In this work, SiO₂-encapsulated copper particles/PA12 (Cu-SiO₂/PA12) composite powders were prepared by electroless composite plating, and the laser sintering behavior was investigated. Results showed that Cu, Cu₂O, CuO, and SiO₂ (Cu-SiO₂) composite particles were plated on the surface of KH550-modified PA12 powders. The Cu-SiO₂ particles existed independently on PA12 surface, and the size was around 200 nm. The melting temperature and crystallization temperature of Cu-SiO₂/PA12 composite powders were 183^∘C and 150^∘C. The results indicate that the selective laser sintering (SLS) process involved the contact of Cu-SiO₂/PA12 powders, the formation of sintering neck, the growth of sintering neck, and the formation of fused solid. The Cu-SiO₂ composite particles uniformly dispersed in the part due to surface tension, and the contact interface was good due to their similar polarity. The Cu-SiO₂/PA12 SLS parts had excellent dimensional precision. The tensile strength of the 15W-sintered Cu-SiO₂/PA12 specimen was 48MPa.

PtO_x films were deposited by direct current (DC) reactive magnetron sputtering in Ar/O₂ mixture atmosphere at substrate temperatures ranging from 200^∘C to 400^∘C. The influence of substrate temperature on the structure, morphology, composition, electrical resistivity and infrared emissivity of PtO_x films was studied. The X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (GIXRD) results revealed that the as-deposited amorphous PtO_x films were mainly composed of PtO and PtO₂ phases. It was found that with the increase in the substrate temperature, the proportion of PtO phase in the films increased, while the electrical resistivity and infrared emissivity of the films decreased with the increasing substrate temperature.

Laser cladding (LC) of the Stellite6-BN-Cu-Y₂O₃ pre-placed powders on the Ti-6Al-4V alloy substrate formed the bulk TiN and needle-like Ti-B compounds reinforced composites, which improved the wear resistance of the substrate surface. The results showed that lots of the amorphous-nanocrystalline phases were produced in such composites; the proper content of Cu was used to refine microstructures, also a large number of the nanocrystals can be formed; the elements such as Co, Ni and Fe in Stellite6 favored the amorphous phase to be formed. The addition of Y₂O₃ improved the fluidity of the liquid metal, also retarding the growth of the dendrite, leading the fine microstructures to be formed, improving the property of the LC composites.

Nanoparticles of alpha ferric oxide ($\alpha$-Fe₂O₃) were prepared by the hydrothermal method. Structural properties of $\alpha$-Fe₂O₃ were determined by XRD, SEM and AFM measurements. The particles had a good matching with standard pattern. Average particle size was about 90nm and the distribution extended from about 20nm to 120nm. Biocompatibility study of ferric oxide nanoparticles against bacteria, parasites, tumor cell line and normal cells was determined. No antibacterial activity was observed for the concentration, of ferric oxide nanoparticles in distilled water, up to 1.5mg/ml vs. E. coli and S. aureus. Moreover, MTT assay was used to determine the cytotoxicity against parasites and cells. Intermediate cytotoxicity (53.30%) of 1.5mg/ml of prepared nanoparticles was noted against L. tropica, while weak cytotoxicity of 5.20% was observed against L. donovani at the same concentration of ferric oxide nanoparticles. On the other hand, the prepared nanoparticles revealed low cytotoxicity (47.28%) against SR tumor cell line, while no cytotoxicity was shown against lymphocytes, as a model of normal cells.

A carbon precursor film was formed on a titanium plate by a hydrothermal method using glucose, and an amorphous film was obtained by carbonization at 400^∘C under an Ar atmosphere. The morphology and composition of the surface was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the interface contact resistance (ICR) under different pressures by simulating the working mode of the fuel cell. The corrosion resistance of amorphous carbon coatings was tested by simulating the proton exchange membrane fuel cells (PEMC). The amorphous coating showed excellent interfacial conductivity and great corrosion resistance, with high potential application in bipolar plates of PEMFCs

In order to reduce the adverse effects on the environment and economy and to avoid health problems caused by the excessively used cutting lubrications, cryogenic machining is drawing more and more attention. In this work, a novel cryogenic machining approach was applied for drilling of carbon fiber-reinforced polymers (CFRPs). According to this approach, CFRP was dipped into the liquid nitrogen (LN₂) and it was machined within the cryogenic coolant directly. Various machinability characteristics on thrust force, delamination damage, tool wear, surface roughness, and topography were compared with those obtained with dry condition. This experimental study revealed that the novel method of machining with cryogenic dipping significantly reduced tool wear and surface roughness but increased thrust force. Overall results showed that the cryogenic machining approach in this study improved the machinability of CFRP.

Surface micro/nanotopography of orthopedic implants plays a significant role in determining their biological performance. In this study, plasma jet was for the first time utilized to modulate the micro/nanostructure of the plasma-sprayed 50% Nb₂O₅-TiO₂ coating on the biomedical Ti alloy based on its high temperature and super-high cooling rate characteristics. Results show that the plasma jet can modulate the shape, dimension and distribution of the surface grains in a process-parameter-dependent manner, thus being able to tailor the micro/nanotopography of the surface coating. In vitro cell culture experiments proved that the plasma jet-induced topographical changes have great effects on the osteogenic activity of the MC3T3-E1 cells cultured on the coating surface.

As an efficient and fast developing surface finishing technique, polishing processes have been widely used in the machining of aero-engine blisk blade. Since a number of processing input variables will influence surface quality and production time, controlling surface finish and machining efficiency require a carefully designed combination of various processing parameters. Therefore, this paper presented a comprehensive multi-objective parameter optimization method that integrates grey relational analysis (GRA), radial basis function (RBF), as well as firefly algorithm (FA). The purpose is to simultaneously obtain the optimal parameter combination for minimum surface roughness and the greatest material removal rate by optimizing rotational speed, feed rate and polishing force in Ti-6Al-4V blisk blade polishing. The hybrid experiments were carried out by combining the orthogonal experimental design with the single-factor experimental design. GRA was run for converting multi-objective response into the single-objective response. Then, RBF was applied to build the relationship between the grey correlation degree and the control variables. Finally, FA was utilized to obtain the optimal grey correlation degree in the range of control variables. The verification tests showed the highest material removal rate of 5.370mm²/s and surface quality of 0.374$\mu$m have been successfully achieved.

TiN, TiAlN, CrAlN and TiAlN/TiSiN films were deposited on AISI H13 hot work steel substrate by cathodic arc evaporation method. Each coating was optimized in laboratory conditions and the highest hardness and wear resistance coatings were taken into consideration for this study.

Morphological properties, chemical compositions, crystallographic structure, nano hardness and adhesion strength of coatings were analyzed with SEM, AFM, EDS, XRD, nano indentation and scratch resistance tester. Wear experiments were performed using ball-on-disk tribometer against Al₂O₃ ball of 6mm diameter and wear volume of coatings were measured using optical profilometer.

Wear experimental results revealed that all coated samples showed higher wear resistance and hardness than uncoated AISI H13 steel substrate. The highest wear and scratch resistances as well as nano hardness were attained for CrAlN coating. TiAlN coating has the lowest scratch resistance and wear resistance. Adhesive wear mechanism was the dominant wear mechanism for CrAlN coatings which is the highest wear resistant coating. Abrasive wear mechanism was the dominant wear mechanism for TiAlN coatings which is the lowest wear resistant coating.

A theoretical study was carried out of Cu_mCo_n-O₂-H₂O ($2\le m+n\le 7$) clusters using density functional method. The results indicate that O₂ and H₂O molecules are adsorbed at top sites. The presence of H₂O promotes more charge transfer to anti-bonding orbitals of O₂ molecules which can lead to the elongation of O–O bond. And the effect of charge transfer suggests the occurrence of chemisorption. Comparison between Cu_mCo_n-O₂ and Cu_mCo_n-O₂-H₂O, PDOS are also discussed.