Key Engineering Materials Vols. 336-338

Abstract: A kind of gradient thermal and environmental barrier coating applied in internal combustion engine is brought forward to improve its reliability, emission and efficiency. The multi-layer plate and cylinder models are established for the simulations of heat transfer and thermal stress in the coatings. Both the theoretical and the numerical analysis with multi-layer cylinder model with coating inside are carried out and compared. The results show good agreement.

Abstract: Ion-beam sputtering deposition is a physical deposited method which uses accelerated ionbeam to sputter oxide or metal targets, and deposits atoms on substrate. Thin films of yttrium-stabilized zirconia (YSZ) were deposited on Si (100) wafer and NiO/YSZ plate. Scanning electron microscopy and transmission electron microscopy with EDS were employed to study the microstructural and chemically stoichiometric results of the films and the crystal growth process by various heat treatments. X-ray diffraction was also used to analysis crystalline phase of the YSZ films. The influence of different targets, substrates deposited efficiency and the properties of the film will be presented and discussed.

Abstract: Al2O3-Al2Cu3 multiphase coatings were prepared on the surface of steel by reactive flame spray. The binding strength, microhardness and abrasion quality of the coatings were measured and analyzed. The influence of the agglomerate size on the properties of the coatings was emphatically studied to choose suitable size range for Al-CuO reactive system. The results showed that coatings prepared by using –150∼+250 meshes agglomerates exhibited good mechanical properties.

Abstract: Silver doped titania-silica films were fabricated by two-step route of sol-gel method using Ti(OC4H9)4, Si(OC2H5)4 and AgNO3 as the precursor materials. The films were annealed at temperature from 350°C to 560°C for a period of time ranging from 15min to 90 min. Optical properties of the films were characterized by UV-visible spectroscopy and the state of silver in the titania-silica films was investigated by XRD patterns. It was found that the annealing temperature and time have considerably influenced the coloration of the films, and with the increase of annealing temperature the [111] orientation of silver crystal occurred which make the color of silver doped titania-silica films deepened. The coloration stability of the silver doped titania-silica films was also investigated.

Abstract: Sol-gel coatings of mixed TiO2-SiO2 had been deposited on ceramic substrates by spraycoating technique to study their hydrophilic and photocatalytic behavior on exposure to sunlight or ultraviolet illumination. The range of the films heat-treatment temperature is from 300°C to 500°C. AFM and XRD analysis were used to characterize the crystal structure and surface morphology of these coatings. Hydrophilic property was evaluated by water contact angle measurement under sunlight illumination condition, and photocatalytic activity by decomposition rate of aniline blue under ultraviolet illumination. Attrition resistance experiment was also carried out to test the hardness and adherence strength of these films. The experimental results demonstrate that this coating possesses high photo-activity and excellent adhesion to ceramic substrates.

Abstract: Antimony doped tin oxide (ATO) thin films were deposited onto silica coated soda lime silicate substrate by the sol-gel method using Sb(OC4H9)4 and Sn(OC4H9)4 as the precursor materials. Conductive tin oxide nano particles of different particle size were added into the sols. The films were subjected to heat treatment at t=500) for about one hour. Film structure and surface morphology has been investigated by means of atomic force microscopy (AFM). Room temperature electrical resistivity of the films was measured using the conventional four probe van der paul method. The influence of incorporation of conductive nano particles on the electrical conductivity of Sb-doped tin oxide films was studied. The correlation between the microstructure and the film electrical property has been obtained. The status of the nano particles in the films has also investigated by FTIR spectroscopy.

Abstract: This research is aimed at the development and characterization of a novel bioceramic coating on the surface of pure titanium. Nano-TiO2/HA composite bioceramic coating was designed and developed on the surfaces of pure titanium discs by sol-gel route. The TiO2 anatase bioceramic coating was employed as the inner layer, which could adhere tightly to the titanium substrate. The porous HA bioceramic coating was employed as the outer layer, which has higher solubility and better short term bioactivity. Conventional HA coatings and commercially pure titanium (cpTi) were taken as control. XRD and SEM were employed to characterize the crystallization, surface morphology and thickness of the coatings. The bioactivities of the coatings were evaluated by the in vitro osteoblasts culture. Results show the nano-TiO2/HA composite bioceramic coating has good crystallization and homogeneous, nano-scale surface morphology. And it adheres tightly to the substrate. The in vitro osteoblasts culture exhibits satisfactory bioactivity.

Abstract: Biomechanical models of implanting prostheses into femora by means of press fit, i.e. the mechanics of non-homogeneous layer-like composites, have been used to quantify the press-fit strength and circumferential stress of the interface, when femora are partially replaced by different thicknesses of bioactive ceramic coatings on a prosthesis surface during the initial implant stage. The maximum press-fit strength appears on the interface between femora and Ti alloy prostheses with non-coating; the press-fit strength decreases with the increased thickness of the coating. The circumferential stress displayed as the large tensile stress at the femoral side of the interface; the compressive stress, appeared at the side of the coating and Ti alloy prosthesis. The shearing strength, jointing between the prostheses and femora would be bigger with the thinner bioactive ceramic coatings. Considering the biodegradability of bioactive ceramic coatings, e.g. hydroxyapatite, HA, it is concluded that the optimum thickness of the bioactive ceramic coatings will be about 50-60 microns.

Abstract: In this paper, two-steps digital image correlation method is well advanced with the sub-pixel reconstruction in sub-image by utilizing the higher precision calculation of bicubic spline interpolation value method, and the accuracy of displacement is extended to better than 0.01 pixel, the strain resolution is limited to less than 0.0002 in micro-region. The experimental results show that the method of two-steps digital image correlation is an up-to-date technique to comprehensive investigations of base metal-coating composition at extremely small size scales. In the meantime, influence of crack in base metal perpendicular to interface on coating is directly observed, and the measurement of the residual compressive strain in base metal is performed according to different thickness of coatings. Lastly, the bond behavior between base metal and coating has been quantitatively analyzed, and the experimental results also prove the Ni-Lan coating is combined with base metal by toughened interface.

Abstract: In this paper, the adsorption of human serum albumin (HSA), human serum fibrinogen (HFG) and human serum immune globulin (IG) on surfaces of diamond like carbon film (DLC), diamond film (DF) and graphite has been studied. The adsorption isotherms of single component protein solution and the competitive adsorption of binary system have been investigated by radioisotope 125 I labeling method. Results showed that (1) the adsorptive amounts of HSA on DLC is more than that of HFG, but the adsorptive amounts of HFG on DF and graphite are apparently more than those HSA; (2) the relative competitive adsorption ability of three proteins on DF and graphite surfaces is HFG > IG > HSA, but that on DLC is HFG ≈ HAS > IG, comparison with HSA, there is no apparent competitive adsorption superiority on DLC for HFG. These results indicated that there is no apparent distinction for the adsorption of three human serum proteins on DLC, but the adsorption of HFG on DF and graphite takes precedence in varying degrees. It probably makes rational explanation for the result of blood-compatibility tests in vitro that DLC is good, but DF and graphite are worse.