Key Engineering Materials Vols. 368-372

Abstract: Using the development tool C++ Builder and adopting object oriented programming method, the ceramic/metal gradient thermal barrier coating design software (CCDS) is developed according to software engineering criterion. The CCDS, which has user-friendly interface, is composed of three functional modules: preprocess module, analysis module and post process module. In addition, this software is attached with an optimal design module and an expert module. The calculation and design of the ceramic/metal gradient thermal barrier coating can be carried out by the CCDS, and the numerical results show good agreement with the analytical results.

Abstract: A coupled and uncoupled non-linear thermomechanical finite element analysis using ANSYS have been carried out to analyze the heat transfer and associated thermal stresses during different simulated thermal shock processes, and the results of two analyses are discussed. It indicates that piezocaloric effect can be neglect when thermal shock intensity is mild and piezocaloric effect should be taken into account when thermal shock intensity is severe.

Abstract: The residual stress accumulation of thermal barrier coatings (TBC) during thermal cycling has been simulated by thermal elastic-plastic finite element method. Stability process of thermal barrier coatings during thermal cycling is studied by Melan's static shakedown theorem considering thermal gradients and thermal expansion misfit. The influences of the interfacial morphology of top coat / bond coat (TC/BC) on residual stress and stability process are analyzed. Thus, the residual stress and stability process are affected remarkably by interfacial topography between TC and BC. Accidented interface cause the sudden change of the interfacial residual stress which is harmful to interface bonding intensity and stabilization. It is useful information for studying of the life and final spallation of TBC system.

Abstract: TiB2 coatings were plasma sprayed in air and were studied by XPS. There are five elements in the top surface of the studied coatings, namely, B, C, N, O and Ti. Oxygen pick-up in the coatings results in formation of oxides of boron and titanium. Nitrogen was shown to exist in N-Ti and O-N-Ti in the coating. Depending on the spraying parameters, mono-boride as well as di-boride was also detected in the studied coatings. With careful peak fitting it was shown that oxygen may exist in the coating as dissolved atomic O in addition to as lattice oxygen in the oxide of boron and titanium.

Abstract: Laser cladding technique was used to form Ni3Si intermetallic composite coating reinforced by in-situ formation NbC particles on Ni-based superalloy substrate. The process parameters were optimized to obtain cladding. The effect of Nb-C addition to the microstructure of the coating was investigated. The morphology of reinforcement particles was discussed. The experimental results showed that an excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. The clad coating was very good and free from cracks and pores. The microstructure of the coating was mainly composed of Ni(Si), Ni3(Si, Nb) and NbC. The NbC particles were formed by in-situ reaction between Nb and C during laser cladding process. NbC particles were homogeneously distributed in the composite material. Moreover, the maximum size of NbC particles was more than 4 μm.

Abstract: Transparent and hard Al2O3-SiO2 thin films have been deposited on PET substrate by E-beam evaporation with oxygen pressure ranging from 1×10-5 to 1×10-3 Torr at room temperature. Pressuredependent characteristics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), meanwhile, apparent transmittance and hardness of thin films were evaluated by uv-visible spectroscopy (UVs) and nanoidentor, respectively. The XRD results showed that the amorphous Al2O3-SiO2 film was obtained although the intensity of the broaden peak decreased with oxygen pressure increasing. The similar morphologies and composition were obtained in pressure range. Good apparent transmittance was found, which higher than 85% in the pressure range. Apparent hardness of PET was effectively improved from 2.77 to 5.7 – 6.1 GPa depending on oxygen pressure. However, the critical load of Al2O3-SiO2 film slightly decreased with oxygen pressure increasing.

Abstract: The influence of pre-deposition of homo-buffer layers on film quality is studied for SrAl2O4:Eu2+ (SAO) crystalline film prepared by RF magnetron method. This preparation technique is necessary to prepare high quality films suitable for the development of SAO devices. Crystallinity and surface morphology were characterized by X-ray diffraction and scanning electron microscopy. After introducing a homo-buffer layer, not only the crystalline but also the surface morphology and adhesion of the film were obviously improved. These results imply that the buffer layer relaxes the strain due to the lattice mismatch between SAO and quartz glass, which improved the crystalline and adhesion of the film.

Abstract: Strongly adherent SrAl2O4:Eu films were fabricated on the rough surface of an alumina substrate by a combination of the RF magnetron sputtering technique and a post-annealing treatment. A crystalline SrAl2O4:Eu2+ film was achieved after annealing at 1000°C in reduced atmosphere and it exhibit a intensively green PL and triboluminescence (TL) while an as-deposition film showed the amorphous state and weakly red photoluminescence (PL). It was found that the fabricated films possessed a strong durability of a friction, exhibiting no peeling, cracking, and breaking in the films after TL measurements. These results will facilitate a development of novel TL skin sensors.

Abstract: Magnetite nanoparticles were obtained by liquid phase precipitation method in which the pH value of [FeCl2⋅4H2O], [FeCl3⋅6H2O] and [NaOH] solution were controlled. Then the magnetite nanoparticle were scattered in water solution and put in [Na2SiO3] and [HCl], the resultant of reaction SiO2 can be coated on magnetite nanoparticles surface. The morphology and magnetite properties of the coated nanoparticles were evaluated by XRD, TEM, FTIR and VSM. The SiO2 thin film with nanometer size was coated on surface of nanoparticle, so that the magnetic value is decreased with the coating thickness increasing.

Abstract: Bioactive porous surface on metal implants are benefit for forming the continuous interface with “mechanical interlocking” and “chemical bonding” between implants and bones. In the present study, the main attention was concentrated on fabricating a porous bioactive surface on Ti substrate. Porous surface was first fabricated by two-step etched. Then thin HA coating was deposited on the pre-treated porous Ti surface by sol-gel method and immediately sintered at 500°C for 1 hour. The structure and morphology of HA coating formed on the porous surface were characterized by thin-film X-ray diffrac- tion and scanning electronic microscopy, respectively. Rietveld method and Warren-Averbach Fourier Transfer Analysis were employed to determine the lattice parameters, crystallite size and micro-strain of HA coating. The SEM results indicated that an interconnecting porous surface with cancellous structure and mean diameter about 1/m was etched on the Ti substrate, and the surface was covered by a thin particle coating. The TF-XRD results testified that the thin coating was poor crystalline HA.