Materials Science Forum Vols. 546-549

Abstract: Magnetorheological (MR) fluids are suspensions of micron sized ferromagnetic particles dispersed in varying proportions of a variety of non-ferromagnetic fluids. MR fluids exhibit rapid, reversible and significant changes in their rheological (mechanical) properties while subjected to an external magnetic field. In this paper, a double-plate magneto-rheological fluid (MRF) clutch with controllable torque output have been designed. Electromagnetic finite element analysis is used to optimize the design of the clutch by using the commercial FEA software ANSYS.

Abstract: In this paper, the distribution and variation of resin pressure were tested by a specially designed measuring system, reflecting the resin flow during the process. Based on this system, the effects of the applied pressure, the lay-up of laminate and the variety of bleeder on resin pressure were investigated. It indicated that the transfer of resin pressure along the laminate thickness direction was not instantaneous. The resin pressure of the laminate boundaries and the resin flow behavior both were influenced by the studied factors. These results are valuable for the modification of the resin flow model and the precise determination of the boundary conditions.

Abstract: Electron beam technology (EB-PVD) and equipment for one-stage deposition of advanced graded protective coatings using a composite ceramic ingot for evaporation are described. This technology allows replacing the flat interface between coating layers by a graded transition zones and achieve of a high degree of reproducibility of the composition, structure and lifetime of the functionally graded coating in compare with traditional multi-stages technologies of protective coating deposition.A design of the composite ceramic ingot is considered, as well as the ability to regulate in a broad range the composition, structure and properties of all levels of the graded protective coating including transition zones and coating layers. Examples and variants of advanced graded protective coatings with their structures and properties are given (thermal barrier, hard erosion-resistant and damping coatings) for aerospace and gas-turbine industry application deposited by one-stage EB-PVD process. Total cost of one-stage EB-PVD deposition process at least 2 times less in compare with traditional technological processes of protective coating deposition due to using only one EB-PVD unit and elimination of multistage nature of process cycle.Laboratory and productive electron-beam units designed and manufactured at ICEBT are considered. Development of modern protective coatings, technologies and equipment for their application is focused, primarily, on improvement of the durability and main service properties of the coating/protected item system, ensuring a reliable reproducibility of the coating structure and properties, shortening the cost and time of the entire technological cycle of their deposition. The existing traditional technologies of deposition of multilayer protective coatings, for instance, thermal barrier coatings (TBC), containing a oxidation-resistant metal bond coat and outer low thermal-conducting ceramic layer, are multi-stage, with combination of such processes as diffusion saturation, galvanic coating, plasma spraying and electron beam deposition [1-3]. Use of diverse expensive equipment, availability of intermediate mechanical and thermal treatments, as well as the operations of surface cleaning, apply considerable limitations both on widening of the sphere of such coating application, and their further development in terms of improvement of the structure and properties. The one-stage electron beam technology developed at ICEBT for deposition of advanced protective coatings based on evaporation of a composite ingot and allowing deposition of functionally graded coatings in one process cycle, meets the above goals to a considerable extent [4,5]. The technology is based on the use of the known phenomenon of fractionating at evaporation of multicomponent systems, containing elements with different melting temperature and vapour pressure, and their subsequent condensation under vacuum, allowing the flat interface, for instance between the metal and ceramic layers, to be replaced by a transition zone of the graded composition and structure. Fig.1 gives the schematic and appearance of a composite ingot used for one-stage deposition of advanced graded protective coatings in vacuum by its electron beam evaporation from one crucible. The ingot base material determines the purpose of the graded coating. For instance, Al2O3, TiC, TiB2, B4C, MgO, etc. can be used as the base of the ingot for deposition of hard wear-resistant, erosion-resistant and damping coatings. For the case of TBC, this is zirconium dioxide with additives

Abstract: In the present study, high temperature properties of Ir-modified and Ir-Hf-modified aluminide coatings on Ni-based single crystal superalloy TMS-82+ were discussed. They were prepared by depositing pure Ir and Ir-Hf alloys on TMS-82+ using magnetron sputtering and EB-PVD, followed by a conventional Al-pack cementation process. The effects of Hf addition on the oxidation resistance and top-coat spallation resistance were investigated. Cyclic oxidation test at 1423K for 1h as one heating cycle revealed that while there is a small difference in oxidation kinetics and spallation lives between Ir and Ir-Hf coatings, drastic difference in surface morphology was observed. After 50 oxidation cycles the Ir-modified aluminide coating showed surface rumpling whereas the Ir-Hf modified aluminide coatings kept the flat surface. It was also revealed that excessive addition of Hf promoted the internal oxidation, resulting in the deterioration of substrates. These results agree with the conventional Pt-modified aluminide coatings and Ni-Al-Hf alloys.

Abstract: Chromium (Cr) films were deposited on plain carbon steel sheets by DC and RF magnetron sputtering as well as by electroplating. Effects of DC or RF sputtering power on the deposition rate and properties such as hardness and surface roughness of the Cr films were investigated. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microcopy (SEM) analyses were performed to investigate the crystal structure, surface roughness, thickness of the Cr films. The deposition rate, hardness and surface roughness of the Cr film deposited by either DC or RF sputtering increase with the increase of sputtering power. The deposition rate and hardness of the Cr film deposited by DC sputtering are higher than those of the Cr film deposited by RF sputtering, but RF sputtering offers smoother surface. The sputter-deposited Cr film is harder and has a smoother surface than the electroplated one.

Abstract: Al-Cu-Fe quasicrystals powder was used to prepare the thin films on the surface of the A3 steel by the means of DMD-450 vacuum evaporation equipment. The thin films with different characterization were obtained through different parameters. The microstructures of the thin films were analyzed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Additionally, the nano-hardness and the modulus of the films are tested by MTS and Neophot micro-hardness meter. The results showed that the modulus of the films was about 160GPa. Nano hardness of the films was about 7.5 Gpa. The films consisted of CuAl2, AlCu3. The thickness and the micro-hardness of the films are improved. In same way, with the increase of the electric current, the thickness and the hardness of the films are also improved. Along with increase of the time and the electric current, the wear behavior of the films was improved. To some extent, the microstructure of films contained the quasicrystal phase of Al65Cu20Fe15.

Abstract: In this paper, the preparation of mullite suspension for electrophoretic deposition (EPD) is presented. It shows that the successful deposition of mullite coating is closely related to the weight ratio of mullite powder to ethanol solvent, and the concentration of phosphate ester (PE) in ethanol solvent, which is employed to positively charge the mullite particles in suspension. The polyvinyl butyral (PVB) is necessary as binder in the suspension. With increasing the powder:ethanol weight ratio, the content for the PVB in the suspension will also increase in order to make the deposited layer adhere to the substrate. The compositions of the mullite suspension were optimized and the process was determined based on the surface quality. It provides a new route to develop mullite coating on SiC or Si3N4 ceramic materials for high temperature application.

Abstract: NiCrAlY coatings were prepared by the detonation spraying (DS) and high velocity oxygen fuel (HVOF) spraying processes, respectively. The DS NiCrAlY coating has higher oxidation rate than the HVOF NiCrAlY coating at 1100 oC due to its rougher surface and more mixed oxides. The residual compressive stress in thermally grown oxides (TGO) on the DS NiCrAlY coating is higher than that on the HVOF coating because the θ-Al2O3 to α-Al2O3 transformation causes the tensile stress in the TGO on the HVOF coating.

Abstract: Modified zirconia thermal barrier coatings (TBCs) with segmentation cracks were sprayed onto a TMS 82+ single crystalline substrate. The thermal cycling lifetime of the modified TBC was improved by 10 times compared to that of the traditional non-segmented TBC. Also, the modified coating showed much better resistance to high temperature cyclic hot-corrosion.

Abstract: Compound ceramic coatings were prepared on Ti-6Al-4V allosy by pulsed bi-polar Micro-plasma Oxidation (MPO) in NaAlO2(S1) and Na2SiO3(S2) solution respectively. The coated samples were calcined in argon under 1000 oC. The phase composition,morphology and element content of the ceramic coatings were investigated by XRD, SEM and XRF. After oxidation in argon, The Al2TiO5 of S1 coating surface was decomposed into Al2O3. SiO2 was crystalized in S2 coating with the final proportion of SiO2 to TiO2 on the coating surface is 81:18. The morphology of the ceramic coatings after the calcination was also different. S1 coatings calcined in argon were fine, grains and pores were smaller and were combined tightly with the substrate, on the contrary, S2 coatings calcined in argon cracked on the coating surface and were separated with the substrate. The content of elements in the coatings both changed a little, which may be due to the reaction of the substrate in the oxidation. According to the phase composition and the morphology of the coatings, S1 coatings are better than S2 coatings.