Xiaohong Chen

Analysis of phase in Cu–15%Cr–0.24%Zr alloy

Abstract The vacuum medium-frequency induction melting technology was employed to prepare the Cu–15%Cr–0.24%Zr alloy. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to analyze the phase composition, morphology and structure of the alloy. The results reveal that the as-cast structure of the alloy consists of Cu matrix, Cr dendrite, eutectic Cr and Zr-rich phase. A large number of Cr-precipitated phases occur in the Cu matrix, and Cu 5 Zr particles can be found in the grain boundary of Cu matrix. The HRTEM images prove that there is a semi-coherent relationship between Cu 5 Zr and Cu matrix.

The mechanical behavior dependence on the TiB whisker realignment during hot-working in titanium matrix composites.

Low-cost TiB whiskers reinforced titanium matrix composite (TMCs) was fabricated with enhanced mechanical performances using in situ technologies and hot working. Morphologies observation indicates that needle-like TiB whiskers with a hexagonal transverse section grow along the [010] direction due to B27 crystal structure and its growth mechanism. Mechanical properties tests show that the mechanical behavior of the TiB whiskers reinforced TMCs is dependent on the deformation amplitudes applied in hot-working. The improvement in yield strength by hot-working is attributed to the TiB whiskers realignment and the refinement of microstructure. Models are constructed to evaluate the realignment of TiB whisker during deformation and the increase in yield strength of the composite at elevated temperatures. These models clarify the alignment effect of TiB whiskers under various deformation amplitudes applied in hot-workings and reveals the yield strength dependence on TiB whiskers orientation.

Hydroxyapatite bioceramic coatings prepared by hydrothermal-electrochemical deposition method

The hydroxyapatite(HA) ceramic coating was successfully prepared on Ti6Al4V alloy by the hydrothermal-electrochemical deposition method with constant voltage model. The phases of deposits were analyzed by X-ray diffraction. The releationship between crystallinity and depositing temperature was discussed. The microstructures of hydroxyapatite coating were observed by scanning electron microscope. The experimental results showed that the phases, crystallinity and morphologies of deposits were influenced by depositing temperature (100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C, respectively). The special hydrothermal environment can lower the crystallization temperature of HA. The crystallinity of HA increases firstly and then decreases with the increase of temperature. There is little hydroxyapatite deposited on the Ti6Al4V surface when the depositing temperature is 100 °C. The HA deposition increases with the increase of the depositing temperature. And the HA morphologies are influenced by the depositing temperature.

Microstructures, mechanical behavior and strengthening mechanism of TiSiCN nanocomposite films

Currently, the arguments have existed in the strengthening mechanism and microstructural model of the nanocomposite film due to lack of the convincible experimental evidences. In this investigation, the quarternary TiSiCN nanocomposite films with the different C and Si contents are synthesized by the reactive-magnetron-sputtering technique. The TiSiCN film is characterized as the nanocomposite structure with the TiN nanocrystallites surrounded by the (Si3N4 + C + CNx) interface phase. When the C/Si content ratio is 2:2, the TiSiCN nanocomposite film is remarkably strengthened with the maximal hardness and elastic modulus of 46.1 GPa and 425 GPa, respectively. Meanwhile, the (Si3N4 + C + CNx) interfaces exhibit as a crystallized form, which can coordinate the growth misorientations and maintain the coherently epitaxial growth between the TiN nanocrystallites and interfaces. Through the high-resolution transmission electron microscopy (HRTEM) observations, this investigation firstly provides the direct experimental evidence for the crystallized feature of the interfaces when the TiSiCN nanocomposite film is strengthened, suggesting that the strengthening effect of the TiSiCN nanocomposite film can be attributed to the coherent-interface strengthening mechanism, which is expressed as the “nc-TiN/c-Si3N4/c-C/c-CNx” model.

Preparation of hydroxyapatite-titanium dioxide coating on Ti6Al4V substrates using hydrothermal-electrochemical method

Ti6Al4V substrates were anodized in a 0.5 mol/L H2SO4 solution at applied voltages of 90-140 V. A hydroxyapatite-titanium oxide (HA-TiO2) coating was then deposited on the anodized Ti6Al4V substrates via a hydrothermal-electrochemical method at a constant current. The obtained films and coatings were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectrometry. The microstructures of the porous films on the Ti6Al4V substrates were studied to investigate the effect of the anodizing voltage on the phase and morphology of the HA-TiO2 coating. The results indicated that both the phase composition and the morphology of the coatings were significantly influenced by changes in the anodizing voltage. HA-TiO2 was directly precipitated onto the surface of the substrate when the applied voltage was between 110 and 140 V. The coatings had a gradient structure and the HA exhibited both needle-like and cotton-like structures. The amount of cotton-like HA structures decreased with an increase in voltage from 90 to 120 V, and then increased slightly when the voltage was higher than 120 V. The orientation index of the (002) plane of the coating was at a minimum when the Ti6Al4V substrate was pretreated at 120 V.

Enhanced Saturation Magnetization of Nanocrystalline Cobalt Produced by Surface Mechanical Attrition Treatment

A nanocrystalline surface layer is produced in Co plate by surface mechanical attrition treatment (SMAT). The characterization of microstructure and composition indicates that elements of Fe, Cr diffuse from hardened steel balls into the surface layer during SMAT. The diffusion phenomenon results in the composition deviation in the surface layer, leading to higher value of saturation magnetization(Ms) for nanocrystalline Co surface layer in comparison with its coarse-grained counterpart.

Preparation of copper-graphene layered composites by spark plasma sintering

ABSTRACT In situ chemical vapour deposition-based graphene growth was designed with copper foil as a substrate and used to prepare copper matrix-graphene layered composites by spark plasma sintering. Mechanical properties and corrosion resistance of layered composites were greatly improved when sintered at 700°C and 25 kN for 10 min. Composite had 12% higher Vickers hardness and 30% higher tensile strength comparing with pure copper, respectively. The corrosion potential (Vcorr) of the layered composites shifted towards more positive values and the corrosion current (Icorr) was significantly lower than that of copper. Corrosion inhibition efficiency () was as high as 68.38% and 36.90%, and the corrosion rate (CR) was 0.047 and 0.093 mm year−1 for the parallel sample and vertical sample, respectively.

Microstructure and optical performance of In2S3 thin films grown by chemical bath deposition

ABSTRACT The In2S3 thin films were deposited by chemical bath deposition at different processing parameters. The In2S3 films were well crystallized when grown at pH values in the range of 1.6–2.0. With increase of the sulfide ion concentration and deposition temperature, the formation and growth rates of β-In2S3 crystals improve. Too high sulfide ion concentration and deposition temperature can induce decomposition of In2S3 crystals. When grown at pH value of 1.8, nIn:nS ratio of 1:4 and deposition temperature of 80°C, the In2S3 film can achieve highly crystallized structure, high transmittance of over 80% and proper energy gap value of 2.74 eV.

Synthesis of carbon nanotubes using Cu-Cr-O as catalyst by chemical vapor deposition

A novel powder catalyst Cu-Cr-O applied to the synthesis of carbon nanotubes (CNTs) was developed, which was prepared via ammonia precipitation method. Techniques of thermo-gravimetric/differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been employed to characterize the thermal decomposition procedure, crystal phase and micro structural morphologies of the as-synthesized materials, respectively. The results show that carbon nanotubes are successfully synthesized using Cu-Cr-O as catalyst when the precursors are calcined at 400, 500, 600, and 700 °C. The results indicate that the calcination of the Cu-Cr-O catalyst at 600 °C is an effective method to get MWCNT with few nano-tube defects or amorphous carbons.

Synthesis of Absorber Layer Film for CI(G)S Solar Cells by Selenization after Sputtering

The CuInSe2 and Cu(In1-xGax)Se2 absorbing layer films are prepared by selenization after magnetron sputtering. The influence of selenization parameters, including selenized temperature and time, on microstructure of CuInSe2 thin films was studied by X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Highly crystallized CuInSe2 film could be obtained when selenized at 500°C for 40 min. By using the same selenization technique, high-quality Cu(In1-xGax)Se2 films were also successfully synthesized from two types of CuInGa precursor layers with different structure.