Advanced Materials Research Vols. 816-817

Abstract: To improve the wear resistance of brass substrate while retaining the electrical conductivity, laser cladding was applied to Cu-WC-Ni composite coating on brass using High Power Diode Laser. Microstructures, phase constitution and wear properties are investigated by means of scanning electronic microscopy with energy disperse spectroscopy and X-ray diffraction, as well as microhardness test and speed friction and wear test. The result shows that microhardness and wear resistance of clad coating were improved obviously compared with the brass substrate owing to the addition of WC ceramic phase, when the content of WC is 25%, the hardness of coating is 4 times of substrate, as well the cumulation mass loss is 1/19 of substrate. Electrical conductivity did not change as copper powder had high electrical conductivity.

Abstract: Flowing solution environment containing H₂S/CO₂ was simulated by high temperature and high pressure autoclave. Corrosion behaviors of P110-3Cr pipeline steels were investigated by Weight loss, Scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Energy dispersive spectrometer (EDS). Effect of temperature on corrosion rate and corrosion product was discussed. The results showed that corrosion rate of P110-3Cr steel decrease at the beginning and then increased with rising temperature. The corrosion types are general corrosion. P110-3Cr has resistance to local corrosion. Mackinawite (FeS_0.9) is formed as corrosion product in low-temperature condition. With temperature increasing the corrosion products are dominated by mackinawite (FeS_0.9) and Cubic iron sulfide (Fe₃S₄). When temperature increased to 150 ¡æ, the corrosion products are made up of Hexagonal iron sulfide (Fe_0.96S) and Orthorhombic Marcasite (FeS₂). No siderite (FeCO₃) is detected, the corrosion is controlled by H₂S; Cr is rich in the corrosion scale.

Abstract: In this paper different characteristic parameters using high-k dielectric materials in Metal Oxide Semiconductor (MOS) device have been compared from the theoretical and simulated Capacitance-Voltage (C-V) graphs. The simulation has been done using ATLAS device simulator. The agreement of the specified values while deriving and simulating and that extracted is excellent. Further, the extracted parameters for high-k dielectric materials show an inferior interfacial quality.

Abstract: New materials play an important part in today high and new technology.Superconducting nanomaterial has become the most vibrant in new material research due to its unique physical and chemical properties. This paper focuses on how small-size effect affects superconducting transition temperature, and summarizes the concrete preparation methods of superconducting nanomaterials, hoping to provide a reference for material researchers.

Abstract: The effect of soaking time and temperature of post weld heat treatment on the micro-properties of the welded joints of ASTM4130 steel was investigated by using micro-shear test. The results show that micro-shear test can be adopted to evaluate the mechanical properties of uneven materials such as the welded joint. The micro-strength of the weld, fusion line and base metal is not obviously affected by the soaking time. The width and strength loss of the softened zone slightly decrease with increasing soaking time. The micro-shear strength of the weld firstly decreases and then significantly increases with increasing PWHT temperature. But the BM shows the opposite trend. The width and strength loss of the softened zone are not obviously affected by PWHT temperature. At PWHT temperature of 590 °C, the width of softened zone and the strength loss rate are the largest. In terms of hardness, width and degree of the softened and toughness, 640°C/165min PWHT is preferred.

Abstract: Electrical discharge machining process (EDM) is a process for removing material by the thermal of electrical discharge. EDM process melts and evaporates workpiece material. Some of the melted and all of the evaporated material is then quenched and flushed away by dielectric liquid and the remaining melt recast on the finished surface. The recast layer is called as white layer. Beneath the recast layer, a heat affected zone is formed. The quality of an EDM product is usually evaluated in terms of its surface integrity, which is characterized by existence of surface cracks and residual stresses. The machinability of EDM in terms of the material removal rate and electrode wear ratio was evaluated in this paper. The machining tests were carried out on a copper alloy grade HR750 with a copper tungsten electrode. The workpiece surfaces are analyzed by optical microscope and XRD technique. The formation of crack is not found.

Abstract: Considering the effect of electro-thermal feedback on the thermal stability of multi-finger power SiGe HBT, optimization of SiGe HBT on both Ge doping profile (electrical aspect) and layout (thermal aspect) is demonstrated in this paper. A novel stepped Ge doping profile of SiGe HBT with a grading Ge concentration in base region is proposed to improve the temperature coefficient of current gain, meanwhile, the cut-off frequency of HBT is also increased considerably due to the accelerated electric field caused by the Ge concentration grading. However, there is still an uneven temperature distribution. Therefore, the layout of multi-finger HBT with nun-uniform emitter finger length is optimized to compensate the thermal coupling effects and hence the uneven temperature distribution is improved obviously. It is shown that the device with simultaneous optimization of Ge doping profile and layout could be in thermal stability over a wide temperature range, which presents useful guideline to design microwave power HBTs.

Abstract: 7075-T651 aluminum alloy are widely used in aeronautical applications such as wing panels, but there is no corresponding constitutive model for it now. In this paper, the flow behavior of 7050-T651 aluminum alloy was investigated by Split Hopkinson Pressure Bar (SHPB) and quasi-static compression experiment system. The strain hardening parameters were obtained by quasi-static compression experiment data, and the strain rate hardening parameters at various strain rates (1000-3000s^-1) and room temperature, and the thermal softening parameter at various temperatures (20-300°C) where strain rate is 3000s^-1 were obtained by SHPB experiment data. Then the constitutive equation of 7075-T651 aluminum alloy is obtained based on Johnson-Cook constitutive equation model.

Abstract: The effects of section size on the stress rupture lives of DD6 single crystal superalloy at 980 °C/250 MPa were investigated adopting machined thin-walled slab specimen. Stress rupture fractograph was analyzed. The results show that stress rupture lives of machined thin-walled slab specimen decline slightly with the reduction of section size at 980 °C/250 MPa, and stress rupture lives of thin-walled specimen are slightly lower compared with that of 5 mm in diameter standard cylindrically specimen, however, the stress rupture lives of thin-walled specimen are still about 200 hours. The decrease in effective loading area caused by oxidation is the main factor for the reduction of thin-walled stress rupture lives.

Abstract: Polypropylene (PP) and high density polyethylene (PE) and are two widely used standard plastics which can be combined to give attractive properties. In this study a selected blend of these plastics is further modified by incorporating nanokaolinite clay and e-glass fibre into the matrix, thereby converting the blend into a fibre-nanomaterial-reinforced-plastic (FNRP). In this manner the PP-PE blend can be upgraded for more critical applications requiring strength and light weight. Melt compounding technique was used to prepare FNRP and samples for testing were prepared by injection molding. Most reports suggest that kaolinite clay, though cheap and abundantly available is difficult to disperse in polymer matrix compared to costly montmorillonite clay. This difficulty is overcome by surface modification of nanokaolinite clay by an organic group and the effect is studied using mechanical properties, thermal stability, dynamic mechanical and rheological behavior. Morphological characterization is done by scanning electron microscopy. This study shows that nanoclay and e-glass fibre synergistically modify PP-PE blend. The resulting composite can be preferentially utilized for manufacturing parts of space crafts, ships, submarines etc.