Papers by Author: Fu Hui Wang

Abstract: The corrosion behavior of a nanocrystalline (NC) low carbon steel (LCS) surface film deposited on a conventional polycrystalline (PC) LCS by magnetron sputtering was studied in 0.5 M H2SO4 solution using impedance and potentiodynamic polarization techniques. The corrosion inhibiting effect of a non toxic organic compound (methionine) and synergistic KI additives was also studied. Microstructure characterization by X-ray diffraction and atomic force microscopy revealed no phase changes due to nanoprocessing and the grain size of the NC surface layer was ~ 40 nm. Electrochemical results show that both the PC and NC surfaces underwent active corrosion with no transition to passivation in the potential range studied. Surface nanocrystallization however increased the corrosion susceptibility of low carbon steel more than two-fold, leading to a decrease in interfacial impedance and an increase in the kinetics of the anodic reaction. Methionine inhibited the corrosion of both specimens with comparable inhibition efficiencies. Iodide ions synergistically increased the inhibition efficiency of methionine on both specimens. This synergistic effect was more pronounced for the bulk steel and has been discussed vis-à-vis the more positive surface charge on bulk steel surface at the corrosion potential compared to the nanocrystalline surface.

Abstract: Composite metastable Ti0.5Al0.5N, Ti0.49Al0.49Y0.02N and Ti0.48Al0.48Y0.04N coatings were deposited on a wrought martensite steel 1Cr11Ni2W2MoV for aero-engine compressor blades by arc ion plating respectively all coatings possessed a dense surface and the same B1NaCl phase structure and the lattice parameter increased with increase of the incorporated element Y. Oxidation-resistance of (Ti,Al,Y)N coatings at 800
for up to 500 hr was investigated and the results showed that the introduction of yttrium into the coatings dramastically improved the oxidation-resistance of the coatings in air. The presence of Y in the nitride coatings suppresses the outer diffusion of Fe through the nitride coating. And the oxide of yttrium may segregate to the grain boundaries of oxides, suppressing the outward diffusion of metallic elements in coating and the inward diffusion of oxygen. Besides, the existence of adequate Y in the coatings is in favor of suppression of the growth of oxide crystals, formation layered oxide scale and decrease of compressive stress of oxidation.

Abstract: The most common metallic coatings used in today’s gas turbine engines are MCrAlX (where M is Ni and/or Co and X is one or more reactive elements such as Y, Hf, etc.) type overlay coatings. However, overlay coating techniques (plasma and flame spraying or physical vapor deposition) are line-of-site processes, and so, it is possible not to deposit coating on some surface of the complex turbine components. The diffusion aluminide coatings can solve this problem. A NiCoCrAlY and diffusion aluminide coating were prepared on K38G cast alloy by multi-arc ion plating and low pressure chemical vapor deposition (LP-CVD) techniques, respectively. The isothermal oxidation behavior of K38G and the coatings was studied in air at 900 and 1000 oC. Their hot corrosion behaviors in the presence of 75 wt.% Na2SO4+K2SO4 and 75wt.%Na2SO4+NaCl film at 900oC were studied. The results showed that the two kinds coatings exhibited low oxidation rate at 900 and 1000oC and the presence of salt accelerated the oxidation rate. The NiCoCrAlY coating showed the better hot corrosion resistance than the aluminide coating.

Abstract: (Ti1-xAlx)N(x=0, 0.1, 0.3) coatings were deposited on 1Cr11Ni2W2MoV stainless steel by arc ion plating. The (Ti1-xAlx)N coatings had B1 NaCl structure, however its preferred orientation change from (111) to (220) with the increase of Al content. A number of nodule-shaped spots identified as rutile TiO2 by XRD formed on the surface of TiN coating after corrosion beneath NaCl deposit in wet oxygen at 600 oC. With the addition of Al, a thin scale composed of Al2O3 and TiO2 formed on the surface of the (Ti1-xAlx)N coatings instead of a scale of TiO2 on TiN coating, thereby their corrosion resistance was remarkably enhanced.

Abstract: Two types of Ni-base nanocomposites were prepared by co-deposition of Ni with nano-sized particles of Cr or CeO2, respectively. Both Ni-Cr and Ni-CeO2 nanocomposites were mainly composed of nanocrystalline Ni matrix, in which certain content of nanoparticles of Cr or CeO2 randomly dispersed. The Ni-Cr nanocomposite was used as a precursor for preparing a novel hard Ni/CrN coating by plasma nitriding at 560oC. The Ni-CeO2 nanocomposite was used as a precursor to develop a novel oxidation-resistant chromia-forming coating by low temperature chromizing using a conventional pack-cementation method. The microhardness of the nitrided layer on the Ni-Cr nanocomposite and the oxidation resistance of the chromizing coating on the Ni-CeO2 nanocomposite were both greatly increased, in comparison to the corresponding counterparts, which were obtained by plasma nitriding on a conventional coarse-grained Ni-Cr alloy with similar Cr content and by chromizing on a coarse-grained Ni metal, respectively. The relationships among the microstructures of the nanocomposite precursors and the nitrided/or chromized coatings, and their properties were investigated and discussed.

Abstract: The aim of this work is to investigate the relationship between the deformation microstructure and texture in cold rolled Interstitial Free (IF) steel sheets. In the present research, the cold rolled IF steel sheets with 10%-50% reductions are used to observe the characteristic microstructure and individual orientations by transmission electron microscopy (TEM) and SAED patterns. The experimental results on inter-granular strain homogeneity and dislocation wall formation are given in details in this paper. The results are explained by the analysis of crystallographic gliding and are helpful to improve the prediction of cold rolling textures.