Advanced Materials Research Vols. 299-300

Abstract: The microstructure, high temperature tensile behavior of the DS NiAl-Cr(Mo)-W/Nb alloy have been investigated. The transverse microstructure of the alloy consists typically of eutectic colonies of NiAl and Cr(Mo) phase with white phases segregating at the cell boundaries. The white phase is possibly Cr(Mo) phase containing large amount of Nb and W elements. The longtitudinal microstructure of the alloy is lamellar with the direction basically parallel to the directional solidification direction. The tensile yield strength and ultimate strength of the DS NiAl-Cr(Mo)-W/Nb alloy are much higher than that of the general cast NiAl-Cr(Mo)-W/Nb alloy, and the elongation of the alloy is also higher than that of the general cast alloy. The fracture is debonding along phase boundary and cleavage.

Abstract: F-doped TiO₂ by hydrothermal synthesis method is prepared in this paper. By basis of sunlight and porous nickels as the carriers, the samples were characterized by Transmission electron microscopy (TEM), scanning electron microscopy (SEM), infra-red (FT-IR) and diffuse reflectance spectroscopy (UV-vis). The photocatalytic performances of the samples were estimated by degrading Rhodamine B. which indicates that the reaction of photocatalytic degradation of Rhodamine B follows the zero order kinetic law. The photocatalytic performances are increased by F-doped. And F optimum doping dosage is 2.0%. After calcination at 500°C, the photocatalytic performance of the sample has not been obvious improved.

Abstract: The corrosion behavior of 316L stainless steel was investigated in seawater at different temperature by using cyclic anodic polarization. The results indicated that two 316L specimens with different grain size showed similar pitting potential at 25°C. The increase of seawater temperature led to the linear decrease of pitting potential and repassivation potential. Because the pitting resistance of fine grain steel reduced larger than that of coarse grain steel with increasing temperature, the latter had a higher pitting potential about 60 mV at 85°C. Compared with the coarse grain steel, the fine grain steel showed a longer induction time for pitting at 65°C.

Abstract: A nitrided layer was formed on the NiTi shape memory alloy (SMA) after being irradiated by a continuous wave Nd-YAG laser in a N₂ environment. With optimum process parameters, a compact laser modified gradient layer reinforced with fine TiN particles was achieved. Electrochemical measurements of the laser gas nitrided layer on the NiTi SMA showed that the corrosion potential and the breakdown potential were increased while the corrosion current was decreased as compared with the untreated the NiTi SMA. The polarization resistance of the laser gas nitrided layer on the NiTi SMA was increased significantly while the capacitance was decreased. Based on the EIS spectra, a simple model and an equivalent circuit were proposed to describe the electrode-electrolyte interfaces.

Abstract: The temperatures inside the gas turbine reach up to 1000°C, alloys used for gas turbine components must be oxidation, and corrosion resistant, and stable in structure under high temperature circumstances. A Co-based alloy was cladded on the 1Cr18Ni9Ti stainless steel surface using a high power carbon dioxide laser. The microstructure evolution and hot corrosion properties of samples in 75%Na₂SO₄+25%NaCl saline were investigated. The results show that the microstructures of the cladded layer is fine, and the hot corrosion resistance of the cladded layer was significantly improved because of the formation of a protective oxide film of CoO and CoO•Cr₂O₃. Under high temperature corrosive atmosphere, the high content of Co promoted the formation of the protective oxide film. The refinement of dendritic structures and the formation of Co-based alloy oxides lower the penetration rate of the sulphur ions that induce the intergranular corrosion.

Abstract: Titanium alloys have successfully been used as surgical implants. Laser gas nitriding (LGN) is an effective method to improve the wear and corrosion resistance of titanium alloys. A nitride strengthened uniform layer, free of cracks, was obtained on the Ti6Al4V alloy by irradiating with a continuous wave Nd-YAG laser in a N₂ environment. The microstructure, electrochemical corrosion and tribological behavior of the alloy before and after LGN were studied by SEM, XRD, potentiostat, microhardness tester and tribometer. The results show that the performance and composition of the surface of the Ti6Al4V alloy were significantly improved by LGN, with better corrosion resistance in simulated body fluid and better wear resistance.

Abstract: Specific coatings are frequently used for increasing the life of mechanical parts undergoing severe corrosive and wearing environment. Plasma surfacing has been used to produce high quality coatings with the rapid development of coating technology. In this paper, the dissolution process of WC particles during the plasma surfacing with Fe-based and tungsten carbides composite coatings on AISI 316L stainless steel was studied .The dissolution process of WC particles is investigated by SEM, EDS and phenomenological analysis. Results show that the dissolution of WC particle during the plasma surfacing process is a successive process consisted of dissolution and reaction diffusion. Moreover, the effects of WC dissolved on micro-hardness of coating have been discussed.

Abstract: Microstructure and mechanical properties of hot rolled steel plate strengthened complexly by titanium and molybdenum at different final rolling temperature and coiling temperature were studied by optical microscope (OM) and material testing machine. The precipitation behaviors of precipitates phase were obtained using transmission electron microscope (TEM) with EDS analysis. The results showed that at final temperature 850°C, microstructure of experimental steel were fine, uniform polygonal ferrite and acicular ferrite. With the coiling temperature decreasing from 620°C to 580 °C, the grain of polygonal ferrite became finer, and the amounts of acicular ferrite became more; precipitates phase mainly maintained both coarse TiN and small square round sheet (Ti,Mo)C. On the condition of the final rolling temperature (850°C) and coiling temperature (580°C), experimental steel acquired properties as follows: yield strength 608 MPa, tensile strength 720 MPa, elongation 24%. Ti-Mo composite strengthening effect had achieved, and significantly improved the strength of ferrite steel.

Abstract: Wind tunnel test can not simulate effectively the flow field of fuze electrical machinery at flight test conditions. In order to deeply research the structure of flow field and measure the flow field density out of fuze electrical machinery, the laser dual hologram interferometry was applied and the streaks photos were obtained clearly. To recognize the contours of density field, identification is needed to deal with interference streaks, and the density of local streaks is calculated with interference principle. The hologram interferometry photos of density field were pro-processed in the thesis, for the problem of photos that the left part was much brighter than the right, the method of multiple threshold was used to binary image. It can be seen that the method gives consistent results to a certain extent of human perception and gives ideal results to find uniform regions in the image plane. Then the binary image is thinned by pixels searching algorithm according to the lines to get coordinates of the pixels of each streak and to lay the foundation for extracting density field from density interference streak in future research.

Abstract: The influence of powder mixture of steel slag and blast furnace slag on the physical properties of cement paste was investigated. Besides, the effect of chemical activator on powder mixture was also studied. For these purposes, the powder mixtures with different ratio of steel slag to blast furnace slag were blended with Portland cement. The water requirement of normal consistency, setting time, and soundness of cement were measured. Water glass and anhydrite were used to stimulate the activity of powder mixture. And the microstructure of hydration products was observed using scanning electron microscope (SEM). It was concluded that powder mixture could improve the fluidity of cement paste and prolong setting time. The effect of compound activators was better than a single one. Under the action of activators, the activity of powder mixture reached to the level of S95, when the proportions of steel slag were from 10% to 30%.