Advanced Materials Research Vols. 152-153

Abstract: The microstructure characteristics and tensile properties in a 0.2C-1.5Mn-1.0Al-0.50Si, high strength hot rolled TRIP steel obtained by a new processing based on dynamic transformation of undercooled austenite(DTUA) were investigated. The results show that the main feature of the new technology is that the ferrite was produced by the applied strain during DTUA. Characterization by means of optical and scanning electron microscopy, transmission electron microscopy and X-ray diffraction has shown that the microstructure of the investigated steel contained a ferrite matrix with fine grain size, bainite with small bainitic packets, and high volume fraction of retained austenite with a large number of granular retained austenite. Tensile testing indicates the steels produced by this processing have higher strength (790MPa) and total elongation (35%) as well as low yield ratio..

Abstract: The nanoparticles of Fe3O4 were prepared with chemical precipitation method, and then used sodium oleate and the lauryl sulfonic aid sodium as bilayer to envelope the ultra-fine Fe3O4 particles. Then stabilized water base magnetic fluid was obtained. The crystallization behavior and the surface of Fe3O4 nanoparticles after the modification were investigated with XRD and IR respectively; the particle size was studied with TEM; the magnetic properties were studied with VSM. The mechanism of bilayer surfactants that modified Fe3O4 magnetic nanoparticles was explained, and influencing factors of the magnetic fluid were discussed.

Abstract: According to the empirical electron theory of solid and molecule, the valence election structures of the matrix  of Al-Fe-Si alloy, solid solutions of -Al-Fe and -Al-Fe-Si, precipitated phases of A13(Fe,Si), Al8Fe2Si and Al12Fe3Si and their abilities of the forming bond were calculated, then the relationships between the abilities of the forming bond of the main precipitated phases in Al-Fe-Si alloys and their precipitations and phases transition were studied in this paper. From the results we find that the ability of the forming bond of Al12Fe3Si (637.23) is small, that of Al3(Fe,Si) (670.52) is large and that of Al8Fe2Si (1038.27) is the largest; the larger the cooling speed, the more amount of the precipitated first of Al12Fe3Si, the few amount of the precipitated of Al3(Fe,Si) and Al8Fe2Si; the stability of Al12Fe3Si is smaller than that of Al3(Fe,Si) and Al8Fe2Si, and under high temperature, the phase of Al12Fe3Si can grow up and coarsen and even change into Al3(Fe,Si) and Al8Fe2Si.

Abstract: Effects of different impact angles such as 45°and 90°on the erosion-abrasion properties of eutectic Al-Mn alloy and its composites reinforced with Al2O3 particulates were studied by rotating erosion-abrasion test, and the microstructure and the worn surfaces were analyzed. The results show that the as-cast Al-Mn alloy is composed of aluminium-manganese solid solution, MnAl6 and Al11Mn4 phase, while the δ-Al2O3 particles are included in the composites besides the aforementioned microstructures. With elongating the erosion time, the wear rates of the Al-Mn alloy and its composites increase at the impact angle of 90°, whereas they firstly increase and then decrease , and there is a maximum at 45°. The distortion wear caused by the normal stress is dominant at 90°, which lead to the erosion pits on the worn surface. However, the cutting wear by the shear stress is predominant at 45°, which result in the ploughs.

Abstract: A wedged load test method is used to evaluate the adhesion strength of high-strength coatings, which have been processed with various sintering parameters. In this test, for stress concentration at cut tip, cracks are always induced and expanded rapidly cross the interface between coating and substrate. Macro-fracture and SEM image of coating interface of high-strength coating are characterized using optical microscope and scanning electron microscopy (SEM), respectively. In order to evaluate the bonding properties between coating and substrate effectively, corresponding finite element (FE) analysis has been conducted to evaluate the adhesion strength of high-strength coating. And stress distributions cross the interface of high-strength coating are obtained. The stress analysis can help to evaluate the bond strength of high-strength coating. Because of small specimen and contact relationship between wedged pressure head and wedged cuts, complex stress state is affected by many factors resulting from interface, and also by the thickness of coating.

Abstract: This study investigated the effects of Fe2+ on the cell growth and hydrogen production to Biohydrogenbacterium R3 sp.nov. in the batch test. The hydrogen production got the maximum of 12.54mmol/L when the concentration of Fe2+ was 40 mg/L and the hydrogen content, OD600nm, glucose consumption and the concentration of ethanol had the maximum of 45.2 %, 1.31 g/L, 92 % and 1073.34 mg/L respectively when the concentration of Fe2+ was 100 mg/L. The phenomenon of feed back appeared when the concentration of Fe2+ exceeded 100 mg/L.

Abstract: A new experimental system is presented to make hydrogen by hydrolyzing Zn nano-particles in a cyclone reactor, in which the chemical reaction and gas-solid separation are carried out simultaneously. The gas-solid form a three-dimensional, turbulent flow-field induced by strong revolving force. The turbulent moving improves the efficiency of heat and mass transfer, which is favorable to chemical reaction. And the Zn nano-particles of 10-20nm preheated at about 523K can react with water steam rapidly. XRD and TEM analysis shows that the solid product consists of ZnO and Zn and has a blended morphology of nano-rods and nano-flakes. The gas-solid separation efficiency primarily depends on the inlet velocity when the particle size distribution is determined, and the particle resident time in the reactor has close relation to Reynolds number of gas inlet. It is confirmed that the steam inlet velocity of 10m/s and Ar inlet velocity of 5m/s are favorable.

Abstract: Different alloys with the minor Sc, Zr and Ti additions were prepared. Microstructures and mechanical properties of the alloys were studied. The results show that the Al-0.25%Sc-0.2%Zr alloy has smaller grain than that of the Al-0.25%Sc alloy, grains of which change from the columnar structure to the fine equiaxed structure because of 0.2%Zr addition. The as-cast Al-0.25%Sc-0.2%Zr-0.03%Ti alloy has the finest grain and the highest hardness of all the studied as-cast alloys. This behavior can be attributed to the fine Al3Sc, Al3(Sc,Zr) and Al3(Sc,Ti) particles, which not only act as the ideal nuclei for α(Al) but also produce grain-size strengthening and dispersion strengthening. The strength of the Al-0.25%Sc-0.2%Zr alloy is not higher than that of the Al-0.25%Sc alloy after hot extrusion because of the presence of Al3(Sc,Zr) particles with smaller misfit with Al than Al3Sc, which brings the transition of dislocation moving mechanism from Orowan bypassing to shearing of the particles.

Abstract: CrZrCu is extensively used as high electrical, thermal and mechanical performance in spot welding. But when CrZrCu electrode is used in spot welding of galvanized steel sheet, the abrasion, corrosion and oxidation shorten the electrode life rapidly. The electrode is not able to meet the needs of spot welding of galvanized steel sheet .In the paper, double glow plasma discharge surface titanizing was carried out on CrZrCu alloy. The processes of double glow plasma discharge titanizing, surface alloying layer structure were also analyzed elementary. The properties of high temperature oxidation were also researched. The experimental results indicated that in the plasma titanizing alloying layer, the diffusion of titanium element toward the interior of the CrZrCu alloy substrate forms the intermetallic compound named Cu4Ti, which is beneficial to the reinforcement of CrZrCu substrate. The experimental results confirmed that double glow plasma discharge titanizing could greatly improve the high temperature oxidation resistance of CrZrCu alloy. Under the temperature of 450oC and 700oC, the oxidation rate of CrZrCu is about five times of plasma titanzing sample.

Abstract: In-situ (Al2O3+Al3Zr)p/A356 composites were synthesized by melt reaction technology and the effects of yttrium on microstructure and mechanical properties of the composites are investigated. The results indicate that the reinforced particulates Al2O3 and Al3Zr become smaller in size with yttrium addition, the sizes are about 0.5~2μm. The distribution becomes more homogeneous, the morphologies are spheroid-shape and ellipsoid-shape, the ambitus is blunt. The mechanical properties test results show the mechanical properties of the composites are greatly enhanced. With 0.4wt.% yttrium addition, the ultimate tensile strength and yield strength of the composites reach to 388MPa and 296MPa, which are increased 35.6% and 37.0% comparing with no yttrium addition, respectively. The effect mechanisms of yttrium are discussed.