Surface Review and Letters

Ion beam assisted deposition (IBAD) was applied to produce TiN coatings on carburized steel substrates. Low deposition temperatures (~50°C) were applied to prevent distortion and softening of previously heat-treated substrates. Mechanical properties of all studied coatings are comparable to those obtained at usually used high temperatures. In order to improve adhesion between TiN coating and substrate, an interfacial layer was prepared by ion beam mixing of Ti atoms and steel substrate. The adhesion strength evaluation revealed significant improvement compared to the coatings produced without the ion beam mixed interfacial layer. Adhesion increased with increase in thickness of the interfacial layer. Substrate roughness was varied systematically in order to determine its influence on adhesion strength. The research was conducted for a rarely studied domain of low roughness (Average roughness Ra below 50 nm). The results of scratch tests revealed improvement of adhesion with increase in substrate roughness. This adhesion trend is different from the one reported by other authors who used rougher substrates. Two groups of opposing mechanisms acting during adhesion testing were identified. It appears that there exists an optimum roughness below which adhesion strength increases, and above which it decreases with the increase in substrate roughness. Accordingly, applying an expensive surface finish does not have to be a guarantee for achieving the appropriate adhesion of TiN coatings deposited at low temperatures.

High quality Co-doped ZnO films with good reproducibility have been prepared under different oxygen partial pressure by radio-frequency magnetron sputtering. These films were characterized using numerous characterization techniques including X-ray diffraction, electrical transport, and magnetization measurements. The effect of oxygen partial pressure on the structural, magnetic, and electrical properties of Co-doped ZnO films has been systematically studied. It was found that the structural, magnetic, and electrical properties of Co-doped ZnO films are dependent on oxygen partial pressure. The saturated magnetization of Co-doped ZnO films rapidly increases with decreasing oxygen partial pressure, whereas the resistivity decreases with decreasing oxygen partial pressure. Our findings indicate that the magnetic and electrical properties of Co-doped ZnO films can be tuned by careful control of oxygen partial pressure. In addition, it was further demonstrated that the oxygen vacancy defect is absolutely necessary to induce ferromagnetic couplings in Co-doped ZnO films.

The fabrication process of Si-steel thin-strip by twin-roll continuous casting was described and the quality of the obtained Si-steel thin-strip was measured. Si-steel strips with 0.5–6.5 wt.% Si content were successfully prepared, and proper parameters including pouring temperature, height of molten pool, casting speed and pouring head mode were optimized, and their mechanisms were discussed. The relationship between quality factors of Si-steel including cracks, strip thickness, impurity and process parameters such as Si content and so on were discussed. The morphologies of the strips with different Si content were studied.

Laser cladding of the Fe₃Al + B₄C/TiN + Al₂O₃ pre-placed powders on the Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiN/TiB₂ composite coating, which improved the wear resistance of the Ti-6Al-4V alloy surface. In this study, the Ti₃Al/Fe₃Al + TiN/TiB₂ composite coating has been researched by means of X-ray diffraction and scanning electron microscope. It was found that during the laser cladding process, Al₂O₃ can react with TiB₂, leading to the formations of Ti₃Al and B. This principle can be used to improve the Fe₃Al + B₄C/TiN laser-cladded coating on the Ti-6Al-4V alloy. Furthermore, during the cladding process, C consumed the oxygen in Fe₃Al + B₄C /TiN + Al₂O₃ molten pool, which retarded the productions of the redundant metal oxides.

To improve the oxidation resistance of the SiC-MoSi₂ coating prepared by two-step pack cementation, a liquid Si infiltrating method was adopted to modify it. The phase composition and microstructure of the coatings were analyzed by XRD and SEM. The results show that the size and number of the cracks in the modified coating decreased evidently after infiltrating Si. The oxidation test results in air at 1773 K show that the mass loss of the SiC-MoSi₂ coating coated carbon/carbon (C/C) composites was up to 1.18% after oxidation for 206 h, while that of the modified coating coated C/C composites was only 0.77% after oxidation for 460 h. The reason is that the cracks formed in the pack cementation process were partly sealed and there were no penetrable cracks in the modified coating. Therefore, there were no direct channels for the oxygen to diffuse into the C/C substrate.

Nanocrystalline supersaturated solid solutions were formed by mechanically alloyed Fe-28Al (in atom percent) from the elemental powder of iron and aluminum. Phase evolution, grain size and lattice strain of these powders were determined and discussed. A thermodynamic model was developed based on semi-experimental theory of Miedema to calculate the chemical driving force for phase evolution. The influence of thermodynamic driving forces, namely the Gibbs free energy of mixing, for the solid solution and the amorphous was discussed and corresponded to the sequence of phase formations during mechanical alloying.

Both ferroelectric Na_0.5Bi_0.5TiO₃ (NBT) and K_0.5Bi_0.5TiO₃ (KBT) are considered as the best known lead-free materials. In this experiment, we prepared NBT and KBT thin films on Pt/TiO₂/SiO₂/Si substrates by metalorganic solution deposition. The structural properties and surface morphologies were measured using X-ray diffraction and atomic force microscopy. The NBT and KBT films show higher leakage currents due to the oxygen vacancies in the films. The remanent polarization and coercive field of NBT (KBT) thin film are 9 (5.2) μC/cm² and 50 (25) kV/cm at an applied electric field of 150 kV/cm. The relative dielectric constants of NBT and KBT are 340 and 316 at 1 MHz, respectively.

The inhibitory effect of some Schiff bases viz. N,N′-bis(2-hydroxybenzylidene)-1,3-diaminobenzene (SB1), N,N′-bis(4-bromobenzylidene)-1,3-diaminobenzene (SB2) and N,N′-bis(2-hydroxy-5-bromobenzylidene)-1,3-diaminobenzene (SB3) on the corrosion of aluminium alloy in 0.5 M HCl acid have been studied using weight loss measurements, potentiodynamic polarization and Scanning Electron Microscopy (SEM). The experimental results showed that these Schiff bases SB1, SB2 and SB3 efficiently inhibit the corrosion of aluminium alloy in 0.5 M HCl medium and found to follow almost similar corrosion inhibition pattern. The potentiodynamic polarization curves revealed that, all the studied Schiff bases are mixed type inhibitors with a predominantly cathodic action and their inhibition efficiencies increased with increasing inhibitor concentration. The adsorption of Schiff bases was found to follow Langmuir adsorption isotherm. SEM study revealed that these compounds protect the metal corrosion by adsorption on its surface to form a protective layer. The inhibition performance depends strongly on the type of functional groups substituted on the benzene ring.

The photoabsorption edge shifting from UV to visible region accompanied with increased intensity and Raman features change was observed for N⁺ implanted TiO₂. Raman spectra prove the formation of TiN_x and oxygen vacancies in the implanted TiO₂, which is considered as the origin of absorption edge shifting. The work may give a hint to increase the photocatalytic activity of TiO₂ in the visible region at the molecule level.

Different aluminide coatings were prepared on oil casing steel N80 at a relatively lower temperature of 530°C for 2 h by pack powder modified with different content of zinc (Zn). The cross-sectional microstructure, element distribution and properties of as-aluminized oil casing steel N80 were investigated by SEM, EDS, micro-hardness test and electrochemical corrosion measurement. Results show that aluminide coating with around 50 μm in thickness can be successfully achieved by a low-temperature pack aluminizing processing with the addition of Zn. Zn in the pack powder can enhance the uniformity and continuity of the coating layer, while it has little effect on the thickness of as-packed coating with the increasing content of Zn from 38.8 wt.% to 84.4 wt.%. As the content of Zn is over 58.8 wt.%, two layer coating consisting of pure Zn layer and Fe–Al aluminide layer can be formed on oil casing steel N80 substrate. Furthermore, oil casing steel N80 with aluminizing coating shows a higher microhardness than that of original one except in the depth range of pure Zn layer, but the microhardness of oil casing steel substrate does not decrease after aluminizing which can be inferred that low-temperature aluminizing processing reported here will not bring any damages on the mechanical properties of oil casing steel N80. Additionally, a lower self-corrosion current density of oil casing steel N80 with aluminizing coating also indicates that low-temperature aluminizing processing is helpful to the corrosion resistance of oil casing steel N80.