Papers by Keyword: EB-PVD

Abstract: Large scale Ni-based alloy sheets are prepared by electron beam physical vapor deposition with and without tungsten added into melting pools respectively. Addition W increased vapor rate and decreased compositional transformation during deposition. Chemical constitution of the sheet prepared through tungsten is more similar to that of the ingot. Microstructure of two alloy sheets is observed by scanning electron microscope (SEM) and atom force microscope (AFM). The results show that both of the sheets consist of columnar grains, whose major axes are almost parallel to the normal direction of the sheet. However, the average diameter of grains of the sheet through tungsten is larger than that of the sheet not through tungsten in minor axis direction. Mechanical properties and failure mechanisms of both sheets are studied. Tensile tests are conducted on a number of specimens. Strength, strain-to-failure are estimated under loading condition. The results show that the sheet prepared by EB-PVD through tungsten has a superior strength and an elongation percentage than that of the one prepared without tungsten.

Abstract: New gadolinium-yttrium zirconate thermal barrier coating(TBC) material is deposited by electron beam PVD method, as an alternative to YSZ TBC layer for gas turbine blade applications. XRD analysis reveals that the new TBC material consists of thermally stable pyrochlore structure. Hertzian and nanoindentation evaluations reveal that gadolinium zirconate materials show superior properties as a TBC candidate material with high mechanical properties. The Y2O3 doping improved hardness and elastic modulus of TBC layers. The indentation stress-strain curves by Hertzian indentation and the load-penetration depth curves by nanoindentation indicate that the new TBC layer has higher damage resistance combined with superior thermal insulation properties rather than commercial YSZ coatings.

Abstract: Numerical method was used to simulate the stress state of thermal barrier coatings (TBCs) under thermal-mechanical coupled environment. The finite element (FE) model was built as hollow tube and boundary conditions including heating rate, cooling air convection and mechanical loadings were considered. The maximum stress locates where maximum temperature gradients is formed. This failure mode is consistent with the experimental results.

Abstract: In the process of preparation of high silicon steel by EB-PVD, the effect of distance between ingot and substrate on the weight percent of silicon in the silicon steel was investigated through specially designed experiment. Energy dispersive spectroscopy (EDS), optical microscope (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD) were used to characterize the weight percent of silicon, microstructure, crystal grain size and phase of the high silicon steel. The experimental results show that the weight percent of silicon in the silicon steel decreases with increasing of the distance between ingot and substrate, when the distance is about 415 mm, high silicon steel can be fabricated by EB-PVD. The microstructure of the high silicon steel was composed of columnar crystal grain, the size of the crystal is about 25-50 μm. The material back to the substrate side is composed of B2 and exhibits strong {400} texture.

Abstract: It has been found that under oxygen partial pressure of ~2×10-6 kPa, the high-temperature oxidation of thermal barrier coatings (TBCs) occurred during an electron beam physical vapor deposition (EB-PVD) process for producing the TBCs top ceramic coating. In the present investigation, two modified bond coats (BCs) of NiCrAlY with Si addition, and NiCrAlY with Co and Hf additions, were developed by Arc Ion-plating technique to study the effects of the EB-PVD process on thermally grown oxide (TGO) formation and growth. The isothermal and cyclic oxidation tests were conducted and the cross-sectional morphologies of the specimens were examined to compare the high-temperature oxidation behaviors of the two TBCs. It was found that a mixed oxide layer have been developed in the as-deposited TBCs with a NiCrAlYSi BC. The mixed oxide layer mainly included Cr2O3, NiO, Al2O3 and their spinel. With the mixed oxide layer, TBCs with the NiCrAlYSi BC showed a superior high-temperature resistance on later high-temperature exposure to TBCs with NiCoCrAlYHf BC, where no mixed oxide layer was observed. The pre-formed mixed oxide layer apparently shortened the time to fully develop a protective α-Al2O3 layer and therefore restrained the TGO growth in TBCs.

Abstract: The sheet metal of a new Ni-based superalloy has been prepared by Electron Beam Physical Vapor Deposition (EB-PVD) technology. The phases, the microstructures and mechanical properties of this alloy before and after heat treatment have been analyzed by X-ray diffractometer, transmission electron microscope, optical microscope, scanning electrical microscope and tensile equipment. Results showed that the size of γ' particles increases gradually and the morphologies of γ' particles changed from spherical shape into cubical shape when temperature increased from low to high. Compared with as-deposited alloy, mechanical properties of heat-treated alloy were improved obviously. It is feasible that superalloy of better properties can be prepared by EB-PVD technology.

Abstract: The thin film deposited by electron beam physical vapor deposition (EB-PVD) on rotating substrate was approached via a kinetic Monte Carlo (KMC) algorithm on a “surface” of tight-packed rows. The motivation is to study the surface morphology distribution of thin film along the substrate radial. Effective deposition rate model and effective incident angle model were established along the substrate radial. Two phenomena are incorporated in the KMC simulation: adatom-surface collision and adatom diffusion. The KMC simulations show that the surface roughness of thin film is small and the changing of surface roughness is small near the side of rotation axis, however, the surface roughness is big near the side of substrate edge, and the surface roughness increases quickly with the increasing of substrate radius when r>300 mm. The simulation results indicate that the effective incident angle is the main factor to cause the changing of surface roughness: the effective incident angle does not reach critical value and the deposition rate difference is small when the radius is less than 300 mm, so the surface roughness of thin film in the scope is small and its changing is small, but when r>300 mm, the effective incident angles increase sharply with radius increasing and all of them are above the critical value, which cause surface roughness of thin film to increase quickly. Experiments reveal that the KMC method can predict surface roughness distribution of thin film deposited by EB-PVD on rotating substrate.

Abstract: In this paper the formation of shear bands in columnar EB-PVD thermal barriers coatings is studied. In particular, critical parameters of nucleation of shear bands, such as contact pressure and initiation of cracks in the columns, are extracted from the experimental results. The pertinence of these parameters is discussed respecting to the stress field induced in the material during the indentation.

Abstract: A NiCoCrAlY bond coating was low-pressure plasma sprayed on a stainless steel sub- strate. Zirconia with 8 wt% yttria was deposited on the bond coating using an electron beam-physical vapor deposition (EB-PVD) method. The top coating had the preferred orientation with the h111i axis direction perpendicular to the coating plane. The distribution of the in-plane residual stress in the top coating was measured using laboratory Cr-K X-rays with a progressive layer removal method. The value of the in-plane stresses was determined by the sin2 method after the separation of the 133 and 331 peaks. The distribution of the out-of-plane strain in the top coating was measured using the strain scanning method with hard synchrotron X-rays. The out-of-plane strain was obtained from the 333 peak which had strong intensity due to the preferred orientation. The measured value of the in-plane stress in the top coating was a large compression, and showed a steep decrease near the in- terface between the top and the bond coatings. The distribution of the out-of-plane stress showed a compression, and its magnitude was smaller than that of the in-plane stress.

Abstract: Yttria stabilized zirconia (YSZ) films with the thickness of up to 12 μm were prepared on alumina and NiO-YSZ substrates by electron beam physical vapor deposition (EB-PVD). The films showed nano-scaled columnar structures depending on the substrate temperature. Electrical conductivity of the YSZ films on alumina was also investigated at the temperature between 700 and 1000oC in oxidizing atmosphere. High activation energy of the conductivity (>1.03eV) indicated that the conduction via grain boundary controlled the ionic conduction in the films prepared by EB-PVD. La0.6Sr0.4CoO3-δ as a cathode was applied on the YSZ/NiO-YSZ in order to evaluate the performance of the YSZ electrolyte.