Papers by Keyword: Microstructure

Abstract: A GMAW additive manufacturing process is performed with H08Mn2Si wire to fabricate a cube forming part. A optical microscope was used to observe the cross section aspect of forming part and the structure mechanism has been analysed. The results demonstrate that the forming part structure presents a characteristic that macrostructure is uniform and microstructure changes circularly. The circularly heating pattern of GMAW surfacing forming results in circular microstructure change and preheating of formed bead to subsequent bead and postheating of subsequent bead to formed bead are primary reason. Electromagnetic stirring effect of longitudinal dc magnetic field to molten pool can break dendritic crystal and refine crystal grain, which is in favor of enhancing forming part performance.

Abstract: 6CrW2MoVSi steel has a refined and even microstructure after heat treatment, the average size of annealing carbide is 0.6 μm; quenching martensite is mainly lath-shaped martensite and only a small amount of acicular martensite, and the size of quenching acicular at 950 °C is smaller than 2.5 μm. The curve of quenching hardness increasing with quenching temperature rising is divided into three sections. In the middle section of quenching between 910 °C ~ 980 °C, quenching hardness presents slow rising trend. After higher temperature quenching, there are low and high temperature tempering precipitation hardening zones. At 220 °C ~ 240 °C tempering temperature, precipitation hardness is HRC54 ~ 58. At 540 °C ~ 570 °C tempering temperature, precipitation hardness is HRC52 ~ 56.

Abstract: The effects of high temperature deformation on transformed microstructure and transformation amount in a high strength bainitic steel were investigated. It indicates that isothermal bainitic transformation is promoted by high temperature deformation. The transformed bainite microstructure is also affected by high temperature deformation, i.e. deformation retards the growth of bainite sheaves, leading to shorter banitie plates. The present study is useful to further understand the effects of ausforming on bainitic transformation.

Abstract: According to continuous cooling transformation curve of pinion steel, heat treatment simulation tests of 8 series were developed. The results show that the microstructure of pinion steel depends on the cooling rate after normalizing. Furnace cooling according to 30°C/h after normalizing can get the typical F+P organizations; Converter cooling after normalizing mixed with some bainite organizations; Furnace cooling with the break after normalizing can get clear stripped bainite organizations.

Abstract: Asymmetric rolling is a promising forming technique offering numerous possibilities of material properties modification and the improvement of technological process parameters. This geometry of deformation is relatively easy to implement on existing industrial rolling mills. Moreover, it can provide large volume of a material with modified properties. The study of microstructure, crystallographic texture and residual stress in asymmetrically rolled titanium (grade 2) is presented in this work. The above characteristics were examined using EBSD technique and X-ray diffraction. The rolling asymmetry was realized using two identical rolls, driven by independent motors, rotating with different angular velocities ω₁ and ω₂. This ensured a wide range of rolling asymmetry: A=ω₁/ω₂. It was found that a strong shear stress induced in the asymmetrically rolled material allowed to obtain a microstructure refinement, texture homogenization and lowering of residual stress.

Abstract: Z11A3M, Z6A3M, Z1.6A1.6M, and Z1A1M coating samples were prepared in HDPS by traditional continuous hot dipping method. The anti-corrosion ability of these coatings was determined by SST, polarization curve and electrochemical impedance. The corrosion products were analyzed by XRD. The surface and section microstructures were observed by SEM. The results showed, the corrosion resistance of 4 kinds of Zn-Al-Mg coated steel is 4 times as galvanized steel. The Zn-Al-Mg coated steel sheets can be self-cured. MgZn₂ and eutectic could be found in all ZAM coating. Zn/Al/Zn₂Mg eutectic can be found in all 4 kind of coatings. The reason for superior corrosion resistance of Zn-Al-Mg coated steel is the decomposition reaction of Zn₅(OH)₈Cl₂ which is retained by Mg. Thus the O₂ diffusing rate is lowered down. Mg acts as PH buffer and the Zn dissolving rate can be reduced. According the results, the application of Zn-Al-Mg coated steel sheets is forecasted.

Abstract: In the present work, the effect of the microstructure of AlSi6Mg2 alloy on its macro-rheological behavior of the steady AlSi6Mg2 alloy is investigated. Specifically, the effect of particle size, packing mode and degree of the agglomeration of particles are analyzed. It can be seen that the apparent viscosity decreases with increasing the particle size (d) if d is between a few μm and 200 μm, while the solid particle size does not affect viscosity except this region. This theoretical prediction is in qualitatively agreement with the experimental data. The trend of the variation of the average agglomerate size with the particle size is the same as the one of viscosity. The packing mode of solid particles in agglomerate is closely related to the solid volume fraction and the characteristics of the alloy system. Subsequently, the state of agglomeration of solid particles which determines the rheology of semisolid AlSi6Mg2 alloy, while the external flow conditions (such as shear rate) influence the viscosity by changing the state of agglomeration. Consequently, the particle size, the packing mode and the average agglomerate size have different effect on the rheological behavior of SSMS.

Abstract: Exfoliated graphite with large expanding volume (EV) was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid, and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. Its preparation conditions were optimized by orthogonal experiment and parallel experiment, and its microstructure was analyzed by scanning electron microscope. The results show that the optimal preparation conditions for the first step intercalation are as follows: the mass-volume ratio of natural graphite (NG) to mixed acid is 1: 4, the volume ratio of nitric acid to phosphoric acid is 1: 2, the mass ratio of NG to potassium permanganate is 1: 0.2, and the reaction temperature is 20~30°C for 40~60 minutes. Those for the second step intercalation are as follows: the mass-volume ratio of acidized graphite (AG) to acetic acid is 1: 5, the mass-volume ratio of AG to nitric acid is 1: 1.5, the mass ratio of AG to potassium permanganate is 1: 0.15, and the reaction temperature is 20~30°C for 40~60 minutes, the EV is 450ml/g under the conditions listed above. The interlayers of graphite are fully opened and become a worm-like fluffy rope.

Abstract: NiCoW alloy powders with and without 0. 4 % La₂O₃ were flame spray welded onto 1045 carbon steel substrate. Vickers microhardness profiles of the coatings were carried out. Sliding wear tests in dry conditions were carried out by means of weight-loss method for several applications in oil industries. For this purpose, Ni-based alloy and high chrome cast iron were used as compared materials. A scanning electron microscope (SEM) was used to analyze the wear phenomena of samples. The result showed that the hardness of the coatings can be improved by addition of 0. 4 % La₂O₃, and the anti-adhesion, anti-scratching, and plastic deformation resistance abilities of coatings are increased with the addition of La₂O₃.

Abstract: Graphite-like carbon films were deposited on DC53 steel substrate by unbalanced magnetron sputtering. The microstructures of the resultant films were investigated by Raman spectroscopy, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD), respectively. Ball-on-disc tribometer was employed to analyze the tribological properties of the film. The results show that the films were dominated by sp² sites. The surfaces are uniform and dense, the sectional morphology of the films present dense columnar crystal. The films have superior tribological properties under different loads, including low friction coefficient (0.18-0.33) and low wear rate (2.53×10^-17m³/(Nm)- 8.47×10^-17m³/(Nm)).