Defect and Diffusion Forum Vols. 334-335

Abstract: Dendritic segregation in deformed samples remains in the form of band structure, which is a high-strained region. The present work investigates the effect of the uphill diffusion process, occurring during deformation, on the dissolution of carbide particles in the band structure. A series of hot compression tests are performed on the cast structure of bearing steel by using a hydraulic testing machine, MTS 810. Cylindrical specimens are deformed in a temperature range of 800°C to 900°C and at strain rates of 5s^-1 and 0.5s^-1. In order to eliminate the recovery process, samples are immediately quenched after the compression. The microsegregation of Cr, Mo, Mn and Si are investigated in the band structure, which shows a tendency of uphill diffusion during deformation process. The results show that the volume fraction of carbides varies with the increased straining. The results also show that deformation causes the fragmentation, dispersion of pearlite in the dendrites and the dissolution of spheroidized carbides in the band structure.

Abstract: In last ten years, leading research centers have been directed to the development of high-Mn steels for manufacturing of parts for automotive industry. The discussed steels with different values of Mn, Al, and Si addition have a medium value of EBU. They usually demonstrate a dominant stress mechanism like twinning induced plasticity TWIP. During the plastic deformation, they may demonstrate a two stress mechanisms like sliding and twinning. The paper presents the results of an analysis of the substructure of high manganese steel after deformation by cold rolling in the context of dominant stress mechanism. The substructure was analyzed by scanning transmission electron microscopy. In the steels, close weaves of dislocations, dislocations tangles, twins and microtwins were observed. It was revealed that the detailed analysis of substructure of the investigated steels after cold deformation could be helpful in determination of the dominant stress mechanism. The obtained results may be used for development of these steels and their plastic deformation models.

Abstract: This paper presents a neuro-fuzzy proportional integral derivative (PID) control technique for improving thermodynamic performance of a metal hydride (MH) reactor via heating/cooling effects generated by a thermoelectric module. The thermal behavior of the MH reactor coupled with a thermoelectric module is numerically studied by mathematical representations of genuine practical applications. It is found that the integrated system has strong nonlinearity owing to thermal characteristics. To obtain the desired performances of the MH reactor, a neuro-fuzzy PID control is used in real-time implementation. A non-linear optimization of a back-propagation technique is applied for fine-tuning the parameters of the neuro-fuzzy PID controller. The simulated results show the effectiveness of the proposed technique compared to conventional PID control.

Abstract: Composite material can be defined as a combination of two or more materials on a macroscale to form a useful material, often showing properties that none of the individual independent components shows. Resin Transfer Molding (RTM) is one of the most widely known composite manufacturing technique of the liquid molding family, being extensively studied and used to obtain advanced composite materials comprised of fibers embedded in a thermoset polymer matrix. This technique consists in injecting a resin pre-catalysed thermosetting in a closed mold containing a dry fiber preform, where the resin is impregnated. The aim of this study is to investigate the effect caused by the use of CaCO₃ filled resin on the characteristics of the RTM process. Several experiments were conducted using glass fiber mat and polyester resin molded in a RTM system with cavity dimensions of 320 x 150 x 3.6 mm, at room temperature, and different CaCO₃ content (0, 10, 20, 30 and 40% in weight). The results show that the use of filled resin with CaCO₃ influences the resin viscosity and the porous media permeability, making it difficult to fill the porous media during the molding process, however it is possible to make composite with a good quality and low cost.

Abstract: In the processing of high performance composite materials, the RTM process has been widely used by many sectors of the industry. This process consists in injecting a polymeric resin through a fibrous reinforcement arranged within a mold. In this sense, this study aims to simulate the rectilinear infiltration of pure resin and filled resin (40% CaCO₃) in a mold with glass fiber preform, using the PAM-RTM commercial software. Numerical results of the filling time and fluid front flow position over time were assessed by comparison with the experimental data and a good accuracy was obtained.

Abstract: In this study, effects of Nd addition on mechanical properties and fracture behaviors of as-extruded Mg-5Al-3Ca based alloy were investigated by a tensile test at elevated temperatures. For all temperatures, addition of Nd elements resulted in further increase of strength both yield and ultimate strength compared to the Mg-5Al-3Ca alloy. At 150°C, the ductility in Nd-added alloys is lower than that of no-Nd addition alloy. However, at 250°C, the ductility in Nd-added alloys is improved for no-Nd addition alloy because of fine grain and suppression of grain growth by formation of thermally stable Al₂Nd intermetallic compounds.

Abstract: Diamonds films have characteristics that are interesting for many optical applications, such as transparency to ultraviolet, visible and infrared light. These applications include use in detectors and windows in processes that involve high temperatures, microelectronics applications and wear-resistant components [. Polycrystalline diamond films can be made in the vapor phase at low-pressure, relatively low temperatures and in the form of auto-supported films, using the CVD process (Chemical Vapor Deposition) [. These films have a significant number of industrial applications, but often have problems with adhesion to metallic substrates. Diamond films can be deposited directly over some metals, but other techniques, such as brazing, can be used [.

Abstract: The reduction of CO₂ emission as the greenhouse gas emitted in the largest volume due to human activities has become a primary focus in the last decade. Generally, in CO₂ gas purification technologies using chemical/physical absorption, the regeneration of solvent is carried out on high temperature and low pressure. This process is quite energy intensive and solvent consuming due to the evaporation loss. The ultrasonic insonation of the solution as a pioneering degassing operation promotes the developing of gas bubbles via rectified diffusion. In the physical models appeared in literature, the effect of the dissolution process on the bubble dynamics is usually neglected due to the different order of magnitudes of the respective timescales. This allows of using constant bubble mass in the equation of motion. Our investigated cases correspond to three different drive frequencies with both coupling and decoupling model settings. Numerical calculations are carried out for an adiabatic CO₂ microbubble by applying a spectral collocation method with Chebyshev polynomials. The obtained results pointed out an enhancement of the rectified diffusion rate by increase of the acoustical frequency at certain pressure amplitude. In addition, the damping effect of the mass diffusion process on the eigen-frequencies can be established in case of subharmonic-and close-to resonance cases. Nomenclature

Abstract: The microstructure of Mg-xAl-3Ca-0.8Sr alloys consists of the α-Mg solid solution, irregular-shaped (Al,Mg)₂Ca, bulky Al₃Mg₁₃Sr and lamellar (Al,Mg)₄Sr phases. The results showed that aluminum has a positive effect on the corrosion resistance of Mg-xAl-3Ca-0.8Sr alloys. The main corrosion product is magnesium hydroxide Mg (OH)₂ which forms a cracked layer on the surface of Mg-xAl-3Ca-0.8Sr alloys.

Abstract: The process of saturation of reinforcement preforms for metal-matrix composite castings is dependent on many different factors. One group of these factors is related to the process of manufacturing of metal-matrix composites with saturated reinforcement. Another group is related to the physical properties of materials used for manufacturing of such composites. The structure of reinforcement preforms is one of such factors. Due to its complexity, its mathematical description is difficult to perform. This structure can be examined and described using physical properties like porosity or permeability. During the conducted analysis presented in the paper, it was checked whether there is a relation between studied physical properties of reinforcement preforms and a degree of their saturation. It was also determined, which of the studied parameters is the best for description of an influence of the geometrical structure of reinforcement preforms on the process of their saturation and in consequence, on the porosity of the obtained composite castings.