Abstract: The purpose of this investigation is focused on brazing Inconel 600 alloy using the nickel-based VZ-2150 filler foil for advanced plate heat exchanger application. Based on SEM microstructural observations and WDS chemical analysis results, both the amount and shape of precipitates in the brazed joint are changed with brazing parameters. With increasing the brazing temperature and/or time results in depletion of the boron from the joint into the grain boundary of base metal. The amount of boride in the joint is greatly decreased, and continuous grain boundary boride will dominate the entire brazed joint. However, the continuous grain boundary boride cannot be completely eliminated by increasing the brazing temperature and/or time.
Abstract: In the present study, Cu60Zr30Ti10 metallic glass powders were prepared by mechanical alloying of pure Cu, Zr, and Ti powder mixtures. Cu60Zr30Ti10 metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and transmission electron microscopy. The metallic glass powders were found to exhibit a supercooled liquid region before crystallization. Cu60Zr30Ti10 bulk metallic glass were synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass powders at 723 K in the pressure range of 0.72 ~ 1.20 GPa. Cu60Zr30Ti10 BMG with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix was successfully prepared under applied pressures. It was found that the pressure could enhance the thermal stability and prolong the existence of amorphous phase inside Cu60Zr30Ti10 powders.
Abstract: Pure molybdenum powder material was processed by equal channel angular pressing (ECAP) with different numbers of passes at the temperature of 400 °C and then Vickers microhardness measurements and scanning electron microscopy (SEM) analysis were conducted. The samples were further characterized with electron back scatter diffraction (EBSD) to examine the grain size. These experimental results exhibit that the powder material is well consolidated and the grains are refined by 2 passes of ECAP processing. In addition, discrete element method (DEM) was used to investigate the deformation behaviour of particles as well as the pores between the particles. The deformation of particles, the distribution of residual porosity and the variation of coordination number in pure molybdenum powder material sample during ECAP were obtained in microscopic scale and all the simulation results are well in line with the microstructure evolution.
Abstract: The thermal insulation function of tungsten-doped vanadium dioxide (V2O5) thin films deposited on non-alkali glass substrate using RF magnetron sputtering was analyzed in this study. Grinded hot-dry V2O5 and tungsten powders, mixed in weight ratio of 98.1:1.9 or 97:3, were pressed at 800 psi for 10 min. These compounds were sintered at 550 or 600 °C for 8 hours, in oxygen gas environments (10 sccm and 0 sccm), to several W-doped V2O5 targets. The surface morphologies of these targets were analyzed by a SEM, and the crystal structure was characterized by a XRD. The experimental studies with reference to the thermal insulation property of V2O5 were conducted under various duration of deposition, substrate temperatures, rf powers and duration of annealing time. The influence of these factors was investigated using the Taguchi method, an orthogonal array L8. The results show that the targets contain a more homogenous structure and a larger grain size with higher oxygen gas flow rate. With a deposition-parameter combination of 60 min (duration of deposition), 300°C (substrate temperature), 150 W (rf power) and 60 min (duration of annealing time), the optimal thermal insulation temperature, 19.3°C, was observed.
Abstract: Boron-bearing high speed steels are widely used in roller materials because of their improved wear resistance and toughness. In present work, aluminum was added into boron high speed steel and the aging-hardening behavior and microstructures of tempered boron high speed steel at various tempering temperatures were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy dispersive spectrometry (EDS) and HR-150A Rockwell hardness tester. The results show that the bulk hardness of boron high speed steel gradually enhances with the increasing destabilized temperature. Aluminum addition cuts down the bulk hardness and delays the hardening process, thus leading to high the hardening value of boron high speed steel shifting to higher destabilized temperature. After tempering process, boron-bearing high speed steel displays precipitate-hardening behavior at the tempered temperature of about 520°C. The bulk hardness of boron-bearing high speed steel achieves 60.5 HRC as a maximum value when the aluminum addition is 0.6 wt.%. More aluminum addition can result in lower precipitate-hardening rate and bulk hardness. The microstructures of boron high speed steel tempered at 520°C consist of eutectic borides and tempered martensite dispersed a lot of secondary precipitates. XRD and TEM results indicate that the precipitate-hardening properties of boron high speed steel depend on precipitates and square degree of martensite
Abstract: The as-cast microstructures and mechanical properties of Al-Si-Mg-Cu-Ti alloys with and without Sc were investigated by metallographic microscope, field emission scanning electron microscope, energy spectrum analysis, transmission electron microscope and universal testing machine. The result shows that adding 0.20wt.% Sc into the casting alloy can refine the grain, change the growth morphology from dendrite to fine equiaxed grain, and the morphology of eutectic Si by rough laminar structure into fine fibrous. The tensile strength of alloy with 0.20wt.% Sc is up to 304.4 MPa after T6 heat treated, which is close to that of 6061 forging aluminum alloy.
Abstract: Abstract: Oxidized and non-oxidized SiC particulates were mixed with Al powder respectively and the two kinds of mixed powders were consolidated at 250°C by equal channel angular pressing and torsion (ECAP-T), which belongs to severe plastic deformation. The interfacial bondings of as-consolidated composites were characterized by SEM images, corrosion morphology and fracture morphology. The results show that after severe plastic deformation, the interfacial bonding between non-oxidized SiC and Al is a kind of mechanical bonding and the consolidation is not firm enough so that the composite has a weak corrosion resistance and its tensile sample has a brittle fracture. However, the composite containing oxidized SiC has a dense microstructure, high corrosion resistance, ductile fracture due to the metallurgical interface.
Abstract: The paper studied the thermal mechanical shearing of waste tire rubber (WTR) by tetra methyl thiuram disulfide (TMTD), a reclaiming agent. The results showed that the mooney viscosity, gel content and crosslink density of the WTR decreased with the increasing TMTD amount. The mechanical properties of recycled rubber were best in the amount of 1% TMTD, which could reach 14MPa and 368%, respectively. The molecular weight of WTR was analyzed by gel permeation chromatorgraphy (GPC). The molecular weight of rubber dropped more faster when the content of TMTD from 0.5% to 1%. The plausible reaction mechanism of TMTD on the process of cross-linking degradation was predicted based on the changes of the mooney viscosity, gel content, crosslink density and the relation between the molecular weight and the Raman spectroscopy of the sol fraction.
Abstract: AbstractThis paper investigated the effect of sensitization time (0h,5h,15h,30h)on intergranular corrosion sensitivity of welded joints of Super304H stainless steel at 650°C by electrochemical impedance spectroscopy (EIS), electrochemical potentiodynamic reactivation (EPR) method and scanning electron microscopy (SEM). EPR results showed that with the increase of sensitization time, the value of reactivation rate Ra increased. Electrochmical impedance spectra of welded joint of super304H for different sensitization time exhibited the similar characteristics. The fitted results showed that the values of Rf decreased with the increase of sensitization time.