Advanced Materials Research Vols. 295-297

Abstract: Fatigue property of 45 steel was studied in this paper with the method of ultrasonic fatigue testing, and SEM was used to analyze microscopic characteristics of the fatigue fracture. Fatigue test results show that: S-N curves descend continuously after 10⁸ cycles, there is no fatigue limit as the traditional fatigue conception describes. Therefore, it is very dangerous to design welded structure working in the ultra-high cycle interval with the fatigue strength corresponding to 5×10⁶ cycles. In the super-long life range, the fatigue property of welded joints is worse than the base metal. SEM analysis shows that: fatigue crack mainly initiates from the defects in the surface or sub-surface.

Abstract: In this paper a bonding-FSSW hybrid method is proposed and the performance and microstructure of bonding-FSSW joints of AZ31 aluminum alloy is examined . The results show that the bonding agent has little influence on the forming and mechanical property of FSSW nugget, the shear-resisting property of joints resulted from bonding with sealing glue and FSSW is equivalent to FSSW joints, in bonding-FSSW with high-strength bonding agent, the shear-resisting property of joints are apparently superior to that of pure FSSW or bonding joints. Tiny and uniform equiaxial grains are formed in the WN(Welding nugget zone) and coarse grains are formed in TMAZ (Thermomechanically affected zone) and HAZ (Heat affected zone), but with unequal size.

Abstract: The aim of the present work was to investigate the effects of specific nitrogen gas additions to argon shielding gas on morphology and microstructure of austenitic stainless steel TIG welds. An autogenous TIG welding process was applied on type 316L stainless steel to produce a bead-on-plate weld. The ferrite content of weld metal was measured using a Feritscope. The results indicated that the arc voltage increase as the amount of nitrogen gas added to the argon atmosphere increases. The retained ferrite content of type 316L stainless steel TIG weld metal decreased rapidly as nitrogen gas addition to the argon shielding gas was increased.

Abstract: In order to obtain better understanding of the friction stir weldability of the magnesium alloy and provide some foundational information for improving mechanical properties of retardant magnesium alloy joints. A retardant magnesium alloy was weld using the method of friction stir welding. The influence of welding parameters on the strength of the joint was investigated. The maximum strength of 230 MPa was obtained from the joint welded at the tool rotational speed of 1000 r/min and welding speed of 750 mm/min.

Abstract: In this paper, the features of weld formation, porosity, arc behavior, microstructure and mechanical properties of 6061 Al alloy thin sheet welds by direct current (DC) double pulse metal inert gas (MIG) welding process are investigated and compared with the traditional DC MIG welding process. Results show that continuous one-side welding with back forming weld beads without spatters, undercuts or cracks can be obtained by using the DC double pulse MIG welding process. The porosity of weld bead can be largely reduced by using the process. The arc of DC double pulse MIG welding is stable without arc blowout, and the metal transfer model of DC double pulse MIG welding is better than that of DC MIG welding. Microstructure of the weld bead by DC double pulse MIG welding shows a dendrite structure and it is fine and uniform. The average ultimate tensile strength and elongation of the weld bead by DC double pulse MIG welding can get to 228MPa, 80% of base metal, and 7.6%, 63% of base metal.

Abstract: The use of temper bead technique in an attempt to eliminate the conventional postweld heat treatment (PWHT) in welding of A508 steel with Alloy 52 filler metal was evaluated. A PWHT at 621°C for 24 h reduced hardness in the heat-affected zone (HAZ) of the conventional welds but led to forming a carbon-denuded zone near the weld interface. The temper bead welding process not only softened the hardness in the HAZ but also diminished the carbon-denuded zone of A508-Alloy 52 welds. Apparently, the temper bead technique provides a convenient and time- saving process for welding/repairing large structural components.

Abstract: Although the original intent of the peer-to-peer (P2P) concept is to treat each participant equally, the heterogeneity is an inherent characteristic of P2P systems. In this paper, according to the previous researches in P2P resource sharing networks, we first conclude and classify the heterogeneity in P2P networks, and then analyze each type of P2P systems that utilize heterogeneity in P2P network. The above analysis and conclusion will become a good guidance to design new resource locating algorithm which takes advantage of heterogeneity in P2P networks.

Abstract: Discontinuous NiTi SMA thin films were deposited on PZT substrate by magnetron sputtering method with a specially designed pore plate. The microstructure and damping property of the prepared composite were studied with X-Ray diffraction, scanning electric microscopy and dynamic elastic modulus apparatus. It was found that the NiTi SMA thin films with physical dimension of the width of less-than or equal to 2mm and distance between the adjacent thin films of 1mm are of best equiaxed crystal structure after crystallization at 600°C. The damping effect of the composite is still caused by PZT and the damping value is generally lower than that of pure PZT, about 9.9%.

Abstract: Zn_1-xCo_xO thin films on sapphire (0001) substrates were synthesized by laser molecular beam epitaxy (LMBE) method at various temperatures under a work ambient pressure of 5.0 x 10^-5 Pa condition. X-ray diffraction (XRD) spectra, UV–visible transmission spectra and X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra were employed to characterize the properties of samples. All samples were of wurtzite hexagonal structure with the preferential c-axis-orientation. Co²⁺ ions incorporated into ZnO lattice and substituted for Zn²⁺ ions. ZnLMM Auger spectrum implied Zn interstitials existed in sample. The optical transmission of all samples was relatively high in visible region. Two PL emission peaks located at 418 nm and 490 nm were assigned to the electron transition from the Zn interstitials to the top of the valence band and from the Zn interstitials to the Zn vacancies, respectively.