A Mathematical Model on Macro-Segregation Formation for Popular Bloom Continuous Casting Process

A segmented 3-D coupled electromagnetic-thermal solute transportation model, aimed to better understand the macro-segregation formation in the strand during a popular continuous casting (CC) process, has been developed. Based on the model validation by industrial tests, the effect of M-EMS and F-EMS running parameters on the segregation distribution were subsequently carried out. It is shown that the simulated solute segregation profile in the W-shape along the casting thickness direction is in a good agreement with the measured profile. In the initial solidification shell with thickness in 0.020 m, the solute segregation degree changes from a positive value to a negative with the increasing distance from strand surface because of the washing effect induced by the impact flow from the nozzle side port and M-EMS. Here, the minimum degree of carbon segregation decreases from 0.976 to 0.875 with the increasing stirring current from 100A to 550A. As the stirring current of F-EMS decreases from 630A to 200A, the minimum segregation degree locating at 0.109 m distance from strand surface increases from 0.805 to 0.967. The carbon segregation degree at the strand center first decreases from 1.10 to the minimum value of 1.06 at the case of 350 A/4 Hz because of the concentration equilibrium for the local decreasing negative segregation induced by F-EMS, and then increases to 1.16 due to the local poor stirring.

An Efficient Model for Predicting the Segregation Profile of Binary Fluidized Beds

In most cases, the stationary fluidized beds are composed of two different particle classes (inert and active particles), and the concentration profile of these binary beds along the vertical axis is crucial regarding the effectiveness of the reactor. The present study introduces a semi-empirical 1D mathematical model for predicting the vertical concentration profile of binary fluidized beds. The proposed model is a developed and applicable version of the so-called Gibilaro and Rowe two-phase model, in which the differential equations describing the jetsam movement in the bulk and wake phases were solved numerically. The main work was to determine the parameters of the basic model, which was carried out by means of an advanced multi-step parameter fitting procedure. A more general form was established, which is based on direct linkage with the operating parameters that can be directly set and measured on the system. Comparisons with very diverse measured data sets available in the literature prove the accuracy of this model. Additional comparisons pointed out that the realization of this model is numerically inexpensive as it is several orders of magnitude faster than the available 2D and 3D models.

Deviation from Regular Shape in the Early Stages of Formation of Strain-Driven 3D InGaAs/GaAs Micro/Nanotubes

Single-crystalline InGaAs/GaAs semiconductor micro/nanotubes have been obtained by the strain-driven self-rolling mechanism. This approach combines the advantages of bottom-up (epitaxial growth) and top-down (postgrowth processing) techniques, offering an exceptional opportunity to realize complex three-dimensional nanoarchitectures by using conventional photolithography and wet-etching processes. The method employed to obtain micro/nanotubes with selected orientation and length is described in detail. By means of high-resolution scanning electron microscopy characterization, we show a clear shape difference between single-wall and multiwalls tubes and we discuss it on the basis of strain release, taking into account also possible shape deformations induced during micro/nanotubes drying. We analyse the In-segregation profile in the nominal In0.20Ga0.80As/GaAs bilayer and we show its effect on the actual diameter of the tubes, concluding that a more accurate description of the structure should consider an In0.20Ga0.80As/In0.10Ga0.90As/GaAs trilayer. This work will be useful to set up reliable methodologies for the realization of strain-driven micro/nanotubes with controlled properties, necessary for their implementation in a large number of application fields.

Homogenisation of Cast Microstructures: Thermodynamic Calculation and Kinetic Simulation

This paper uses a combination of thermodynamic calculation and kinetic simulation to model the homogenisation process of cast microstructure for multi-component alloys. The approach assumes that the solute segregation profile across the half dendrite arm spacing can be scaled to the solute concentration profile during solidification as generated by a Scheil type calculation. When secondary phases dissolve during homogenisation, they are treated as an additional fraction of pseudo-eutectic to the initial solute concentration profile of the primary solution phase. The methodology is compared with the assumptions made by other authors, highlighting the significant advantages in the present treatment. Examples are drawn from a cast nickel-based superalloy.

Quality Assessment and Metallurgical Examination of Laser Welded Sheets

Laser welding of steel 316L sheets is considered and the effects of laser welding parameters on the laser weld quality and metallurgical changes in the weld section are presented. The laser weld quality is assessed through careful examination of weld geometrical features, and the resulting weld microstructure. Metallurgical changes in the weld sites are examined using optical, and electron scanning microscope (SEM). Two levels of heat inputs are used-1500W and 2000W; and two scanning speeds of 2cm/s and 4cm/s are used to laser weld 316L sheets. It is found that at the high laser power intensities, evaporation takes place in the irradiated region and as the laser power intensity increases further, a cavity is formed at the top surface of the welding cross section. A similar situation is also observed as the laser scanning speed reduces. The low diffusivity of the alloying elements at high temperatures preserves the segregation profile. The scattered partitioning of the cells and dendrite boundaries are observed due to the presence of Cr and Mo.