Papers by Keyword: EB-PVD

Abstract: Ti-TiAl multi-layered materials have been prepared by electron beam physical vapor deposition technique. The tensile behavior of samples at room temperature and high temperature was tested, and then the deformation mechanism at different temperature was analyzed according to the fracture surface. The results show that the tensile curves hot-pressed samples have a broad step during the plastic deformation process, and the breaking strain of the sample has been increased for a wide-range. The presence of Ti layers have led to the cracks stagger along the inter-laminar interface or the layer due to which micro laminate expresses a good characteristic of delayed fracture. With the increase of temperature, the bulk modulus and yield strength of multi-layered Ti-TiAl have been increased abnormally due to the anomalous yield strengthening behavior of TiAl intermetallic.

Abstract: Large-sized Ti/Ti-Al micro laminated thin sheet with thickness of 0.12mm was prepared by high-power electron beam physical vapor deposition technology, and then tensile tests of specimen after hot-pressing densification were carried out at room and high temperature, and tensile specimen was examined the fractured surfaces by SEM and OM. It was found that the tensile specimen under room temperature presents a compound quasi-cleavage and intergranular fracture, and a certain plastic deformation of Ti toughening layer was detected during fracture process. Tensile fractured surfaces under high temperature present the feature of compound dimple models and quasi-cleavage, furthermore, the size and the quantity of dimple exhibited an enhancing trend with test temperature increased. Results show that the cracks will stagger along the inter-laminar interface or the layer due to which micro-laminate expresses a good characteristic of delayed fracture. The toughening mechanisms are that the crack deflection and micro-bridge connection caused by the toughening layers increases crack propagation resistance.

Abstract: By using electron beam physical vapor deposition (EB-PVD) technology, Ti-Al thin sheet with dimension of 450mm×450mm×0.2mm was prepared and the microstructure of Ti-Al deposit was investigated by means of scanning electron microscopy (SEM), atom force microscopy (AFM) and X-ray diffraction (XRD), and then the effect on deposit by re-evaporation of Al was explored by calculating the ratio of re-evaporating capacity with depositing capacity of Al on the substrate. The results indicate that there existed equiaxed crystal and columnar crystal along the cross-sectional may resulted from the transformation latent heats released during the transition course of atoms from gaseous state to solid state, and the variation of target-substrate distance would take effect on the phase composition due to the changing of atoms collision probability and radiant heat quantity absorbed by substrate. The effect on deposit by re-evaporation of Al could be neglected because the re-evaporating capacity of Al was far below that of the depositing capacity.

Abstract: A microlaminate consisting of Ti and α2-Ti3Al+γ-TiAl has been synthesized using electron beam physical vapor deposition technique. The microstructure and various properties have been explored. It is demonstrated that the nano-hardness and elastic modulus of Ti layer and Ti-Al layer are of gradient distribution according to the distance to the interface layer which may be results from the pile-up effect and the stress concentration at interface. The presence of Ti layers will lead to the cracks stagger along the inter-laminar interface or the layer due to which micro laminate expresses a good characteristic of delayed fracture. The toughening mechanisms are that the crack deflection and micro-bridge connection caused by the toughening layers increases crack propagation resistance.

Abstract: As the top coating, zirconia with 4 mol% yttria was electron beam-physical vapor deposited (EB-PVD) on the bond coating of CoNiCrAlY. The substrates were rotated during EB-PVD process and the rotation speeds were 5 (R5) and 10 rpm (R10). The thickness of the top coating was 0.12 mm. In order to investigate the change of the internal stress in the top coating under a heat cycle, the specimen was heated from a room temperature to 1293K, the internal stress was measured in-situ by a strain scanning method with hard synchrotron X-rays at each temperature step. For the specimen R5, the internal stress increased from about -100 MPa to about 100 MPa with the increase in temperature, then the stress relaxation of the top coating occurred over 1093K. In the cooling process, the internal stress decreased, however, the changing rate of the internal stress was small as compared with the heating process. This was caused by the feather-like structure sintered. For the specimen R10, the internal stress did not show a tension in the heating process, it was caused by the separation between columnar structures.

Abstract: Thermal fatigue damage evolution behavior in thermal barrier coatings (TBCs) was studied, by employing the originally designed two dimensional ring-shape TBC specimen. The TBC specimen consisted of Ni-based superalloy IN738LC substrate, bond coat, and 8 wt.% Y2O3-stabilized ZrO2 (YSZ) top coat. The top coat was fabricated by electron-beam physical vapor deposition (EB-PVD) method with 250 micron-meters in thickness. Three kinds of MCrAlY bond coat alloys were specified as an experimental variable. Through the work, special attention was paid not only to the failure life of TBC specimen, but also to the underlying failure mechanisms. Some problems have been also pointed out, on feeding back these experimental findings to engineering applications.

Abstract: Yttria Stabilized Zirconia (YSZ) films were prepared by electron beam physical vapor deposition (EB-PVD) technique with a high deposition rate up to 1μm/min. An improved sin2ψ method was employed to analyze the residual stress of films by means of grazing incidence X-ray diffraction (GIXRD). The result of residual stress measurement reveals that residual stress of YSZ film is compressive stress and keeps a linear relationship with the deposition temperature, which is induced mainly by the thermal expansion mismatch between the film and substrate. The XRD result of films, prepared with different incident angles, demonstrates that the films show preferred orientation evidently. Furthermore, a parameter ωhkl was introduced from the inverse polar figure measurement theory to reveal the degree of preferred orientation clearly. The calculating result of ωhkl value indicates that the preferred orientation of different specimens changes with the incident angles, which is due to columnar growth pattern of films prepared by EB-PVD. In order to characterize the crystallographic texture visually, XRD with 2D detector system was used to analyze the texture of films. The result shows that Debye rings appear asymmetric intensively, which denotes the existence of preferred orientation directly and agrees with the calculating result of ωhkl value.

Abstract: The process of Electron Beam-Physical Vapor Deposition (EB-PVD) preparing SiC coating by Electron Beam evaporating 3C-SiC ingot on stainless steel (SS) substrate was firstly discussed as a preliminary estimation from thermodynamic viewpoint. The results show that, with the temperature increasing from 2500 to 3400 K, the purity of SiC coating increases from 0.58 to 0.734.

Abstract: Large-sized Fe-based ODS (Oxide Dispersive Strengthen) high-temperature alloy sheets were successfully synthesized by EBPVD (Electron Beam Physical Vapor Deposition) technique. The sheets were about 120μm thick, and having a diameter of 1000mm, whose surface roughness was less than 1μm (Ra<1μm). The microstructures were examined by SEM (Scanning Electron Microscope). The grain size was 1-4μm. When the substrate temperature was 600°C, the sheet had sharp irregular polyhedral grain, and when the substrate temperature was 700°C the sheet had quite regular grains. The morphological orientation angle increased with the distance from the center of the sheet. During the first period of deposition, the sheet was growing in a G-L-S mode, which corresponded with the corn-like microstructure in the cross-section. While during the final period, the sheet changed into a G-S growing mode, which corresponded to the smooth columnar microstructure.