Papers by Author: Ming Wei Li

Abstract: Large-size Ni-based alloy sheet was prepared by electron beam physical vapor deposition (EB-PVD). Thickness uniformity of large-size sheet for application is important. Based on the Knudsen’s cosine law and the character of the evaporation during EB-PVD, thickness distribution model of condensate on rotary substrate by EB-PVD was established. The thickness model is not consistent with the traditional cosine law, but cosnθ relationship, n=5.3 in this paper. The predicted data of thickness model agrees well with the measured data. The thickness distribution model is not limited to specific vapor source material, therefore, it provides significant insight on the thickness distribution profile for film, coating and sheet deposited on the rotary substrate by EB-PVD.

Abstract: ARMOR TPS panel is above the whole ARMOR TPS, and the metal honeycomb sandwich structure is the surface of the ARMOR TPS panel. So the metal honeycomb sandwich structure plays an important role in the ARMOR TPS, while it bears the flight dynamic pressure and stands against the flight dynamic calefaction. So the active environment of metal honeycomb sandwich structure is very formidable. We have to discuss any extreme situation, for reason of making sure aerial vehicle is safe. And high-frequency vibration is one of active environment. In this paper we have analyzed high-frequency vibration response of metal honeycomb sandwich structure. We processed high-frequency vibration experiment by simulating true aerial environment. Sequentially we operated high-frequency vibration experiment of metal honeycomb sandwich structure with cracks, notches and holes. Then finite-element analysis was performed by way of validating the experiment results. Haynes214 is a good high temperature alloy material of both face sheet and core at present, so we choose it in this paper.

Abstract: The unitary thermal insulation fiber materials can not satisfy rigorous high temperature environment usually. New inorganic coatings were prepared by adding SiO2 aerogels super-insulation powder into high temperature adhesive. Aerogels are high dispersive solid materials which consist of colloid particles or high polymer molecule and have continuous random network structure filling with gaseous dispersive medium. The coatings with super insulation function were made by means of adding thermal-proof materials to the coatings. The microstructure of light porous power and the states of coatings on the surface of fiber paper under different state were observed by scanning electron microscope (SEM). The insulated effect of the composite materials was tested by considering thermal conductivity. On the basis of this, the coatings on the surface of fiber paper were optimized according to the material thermal-insulation performance and the materials that could be satisfactory to the service conditions were made in the end. The results show that silica aerogels powder is dispersed equably in high temperature adhesive. The new inorganic coatings possess themselves of good thermal-insulation effect and can be used as insulated space-layers. The insulation ability of fiber paper is improved obviously.

Abstract: A 2D kinetic Monte Carlo (KMC) simulation has been applied to study the microstructure of Ni-Cr film deposited by physical vapor deposition (PVD) for variable incident angle. In the KMC method, two phenomena were incorporated: adatom-surface collision and adatom diffusion, the interaction between atoms was described by embedded atom method and jumping energy was calculated by molecular statics calculations, initial location of adatom was located by Momentum Scheme. The results reveal that there exists critical incident angle, which is 35˚ for Ni-Cr thin film. When incident angle is less than 35˚, incident angle have less affect on surface roughness factor and packing density, compact films with smooth surface are obtained, their surface roughness factor is bellow 1.12 and packing density is more than 99.6%. However, when incident angle is more than 35˚, surface roughness factor increases quickly and packing density decreases sharply with incident angle increasing: surface roughness factor increase to 1.5 and 2.3 for incident angle of 45˚ and 60˚ respectively, packing density is below 99% and 96% accordingly. Which reveal that the self-shadowing effect emphasizes with incident angle increasing when the incident angle is more than 35˚.

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: 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: 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: 2D kinetic Monte Carlo simulation has been used to study the void distribution of nickel thin film prepared by physical vapor deposition, and embedded atom method (EAM) was used to represent the interatomic interaction. Packing density and surface roughness were studied as the functions of deposition rate, substrate temperature and incident angle. The results reveal the existence of critical substrate temperature and critical incident angle, and higher substrate temperature, lower deposition rate and appropriate incident angle are advantaged to prepare the compact thin film with excellent mechanical properties.