Defect and Diffusion Forum Vols. 297-301

Abstract: This paper presents a numerical study of mixed convection heat and mass transfer in horizontal rectangular channels partially filled with porous medium. The main contribution of this research is to characterize how the porous block will create a heterogeneity that will induce a change on the Poiseuille-Rayleigh-Benard (PRB) fluid circulation dynamics. For a broad range of dimensionless parameters, which control the mixed convection, we show that the effect of the insertion of the porous block changes the thermal and solutal boundary layers; we find that the exchanges are intensified near the sidewalls in the porous region compared to upstream and downstream of the porous medium; and inversely in the core region. We describe, also, the onset of the longitudinal rolls at both upstream and downstream of the porous region. And finally, we compared the heat transfer, for different positioning of the porous medium with the purely fluid mixed convection.

Abstract: In order to explore the formation process of collapse-type shrinkage of eucalypt wood, the collapse-shrinkage properties in Eucalyptus urophylla and E.cloeziana wood under different heat-treatment conditions were systematically investigated by using frozen drying, and simultaneously creative assessments on their collapse-type shrinkage process were conducted based on the novel concepts of both transient collapse and maximum transient collapse advanced for the first time. The results indicated that, for lower-density E.urophylla, total shrinkage and residual collapse under both heat-treatment regimes increased with increasing temperature. As compared to intermittent heat treatment, the above two indices at three levels of temperatures in continuous heat treatment displayed relatively larger values, and exhibited down-open-parabola type; For higher-density E.cloeziana, only higher collapse phenomenon in the part near to the pith were observed, and similar to E.urophylla, while almost slight and /or no collapse occurs in the middle heartwood and sapwood, and shrinkage and collapse in continuous heat treatment is slightly larger than those in intermittent heat treatment, and both shrinkage and collapse take on up-open-parabola type. Trends of radial variation of both parameters for both species in continuous heat treatment were consistent with those in intermittent heat treatment. It can be speculated that the mechanism of the difference in collapse-type shrinkage characteristics between two heat-treatment patterns are that the more types of cells and the more number of cells participated in the collapse development, and the more transient collapse, especially maximum transient collapse, is transformed into the permanent set to develop the residual collapse for continuous heat treatment than the intermittent heat treatment. Therefore, it is very crucial for lower-density susceptible-collapse eucalypt to manage to prevent maximum transient collapse from being transformed into permanent set in the process of drying.

Abstract: Collapse-type shrinkage is the greatest obstacle to prevent planted eucalypts from being used for solid wood products. In order to make the suitable drying schedules for high effective utilization of eucalypt wood, the total shrinkage and collapse on two species of difficult-to-dry E. urophylla and E.grandis wood under continuous and intermittent drying regimes were measured. The results show that total shrinkage and collapse in both eucalypts exhibited higher values for continuous drying than intermittent drying. With increasing drying temperature, total shrinkage and collapse increase in both drying regimes, while the increasing magnitude of both parameters becomes apparently larger for continuous drying than intermittent drying regime, in particular higher temperature condition. Properly elevating drying temperature to make up for the intermittent-waiting time may be allowed for intermittent drying regime. Drying duration at each intermittent drying period has a greater effect on total shrinkage and collapse of eucalypt wood. When more than a drying duration of 6 hours at an intermittent drying period is used, the differences in shrinkage and collapse between both drying regimes are very slight. Intermittent duration at an intermittent drying period has a comparatively larger effect on total shrinkage and collapse. Accordingly, we may draw a conclusion that intermittent drying regime is very likely to be a potential drying one suitable for collapse-prone lower-density plantation-grown eucalypt wood.

Abstract: In this paper, we present results of a study of TiN films which are deposited by Physical Vapor Deposition and Ion Beam Assisted Deposition. In the present investigation the subsequent ion implantation was provided with N2+ ions. The ion implantation was applied to enhance the mechanical properties of the surface. The film deposition process exerts a number of effects such as crystallographic orientation, morphology, topography, densification of the films. The evolution of the microstructure from porous and columnar grains to densely packed grains is accompanied by changes in mechanical and physical properties. A variety of analytic techniques were used for characterization, such as scratch test, calo test, SEM, AFM, XRD and EDAX. The experimental results indicated that the mechanical hardness is elevated by penetration of nitrogen, whereas the Young’s modulus is significantly elevated. Thin hard coatings deposited by physical vapour deposition (PVD), e.g. titanium nitride (TiN) are frequently used to improve tribological performance in many engineering applications. Ion bombardment during vapour deposition of thin films, colled ion beam assisted deposition (IBAD), exerts a number of effects such as densification, changes in grain size, crystallographic orientation, morphology and topography of the films. This paper describes the successful use of the nanoindentation technique for determination of hardness and elastic modulus. In the nanoindentation technique, hardness and Young’s modulus can be determined by the Oliver and Pharr method. Therefore, in recent years, a number of measurements have been made in which nanoindentation and AFM have been combined.

Abstract: The microstructure of as-cast Mg-xAl-2Sn alloys consists of an α-Mg matrix, a Mg17Al12 eutectic phase and a Mg2Sn phase. In as-cast alloys, the Mg17Al12 eutectic phase was located at along grain boundaries. The eutectic phase of the extruded alloys was elongated in the extrusion direction and crushed into fine particles because of deformation during hot extrusion, and the grain size was refined with an increased Al content. The maximum values of the yield strength and tensile strength were 240 MPa and 300 MPa at 9 wt.% containing Al element, respectively.

Abstract: Steels alloyed with Si and Al are used as core material in flux carrying machines, they are commonly called electrical steels, divided into grain oriented and non-oriented when a material without magnetic anisotropy or not is desired and used in transformer and electrical motors, respectively. The appearance of brittle ordered structures when Si+Al content in steel is above 4 m.-% does not always make its industrial production easy. Therefore hot dipping in a Al-Si bath followed by a diffusion annealing was found to be a productive way of steels with high Si and/or Al concentration and to overcome the creation of fragile structures during deformation processes, such as rolling. The formation of different layered Al-(Si)-Fe intermetallics on the steel substrate depends on diverse processing parameters such as bath temperature and composition, immersion time, preheating of the steel substrate and its composition and cooling down to room temperature. This contribution reports the diffusion kinetics of Fe2Al5 products obtained during the hot dipping process in an Al iron saturated and a hypoeutectic Al – 5 m.-% Si baths of ultra low carbon steel and Fe-substrates with 3 m.-% Si, annealed and cold rolled to different thicknesses. The preheating of the samples and bath temperatures were varied between 670 to750°C. Dipping times between 1 to 600 sec. were applied. The different layers and compounds formed were characterized by Scanning Electron Microscopy (SEM), using Back Scattered Electron (BSE) detector and Energy Dispersive Spectroscopy (EDS). The influence of the substrate and bath chemical composition on the growth kinetics of the Fe2Al5 intermetallics was investigated assuming a parabolic law. Si addition retards the growth kinetics and, as result, raises the activation energy from 71.3 to 159.8 kJmol-1, the obtained results are in agreement with the literature.

Abstract: Hot dip galvanizing has proven to provide excellent protection against corrosion of steel for a wide range of applications. Coatings of Zn-Al alloys on steel sheet give a high corrosion resistance due to the corrosion prevention by zinc and the passivation by Al. Many important industrial processing steps require a reliable procedure for process verification. Verification on production or pilot lines is neither economical nor efficient. Simulators for the HDP (Hot Dip Process) allow laboratory scale simulations of the (hot dip) coating and of the consequent annealing processes occurring in industrial production lines, serving for process and product improvement and development. To improve and further develop the production and the final coating properties, hot dipping experiments are performed in a HDP simulator using different substrates, bath compositions and hot dipping parameters. The results obtained by these simulations are transferable to the production process of real continuous galvanizing lines. Important industrial steps of the process can be simulated in the HDPS with a high variability of parameters.

Abstract: The development of arthroplastics places high demands on the materials used for load-bearing elements of orthopedic implants. The most common of implant materials are titanium and cobalt alloys due to their excellent mechanical properties and biocompatibility. Titanium alloys have desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, superior corrosion resistance and so are frequently used for long-term implants. However, poor wear resistance limits their application for tribological systems of artificial joints. Research on improvement of titanium alloys tribological properties have been undertaken, mainly by using thin coatings. The TiN-layers are reported to be most promising in biomedical applications such. Many authors stress that application of TiN layer improve wear resistance of titanium implant alloys. Presented work is focused on comparison of effect of TiN coating on properties of TiAlV and CoCrMo implant alloys. The structure, microhardness, corrosion resistance as well as tribological properties were analysed. The research did not confirmed the good properties of titanium alloy with TiN coating. The results show that matrix metal hardness definitely affects the efficiency of TiN layers.

Abstract: Porous metallic alloys are reported as the prospective biomaterials for restorative medicine due to their unmatched features guaranteeing fixation of prosthesis. Numbers of research are focused on functional properties of porous materials. Especially corrosion behavior seems to differ from the analogue bulk materials. The aim of presented work was to study corrosion resistance of sintered porous implant steel 316L. Samples with porosity in range of 26-40% were fabricated by means of the PM method. Corrosion tests were carried by using an automatic polarization unit Atlas-Solich98 in 0.9% NaCl water solution. The experiments conducted confirm that porous 316 stainless steel possesses a distinct passivation range. The obtained results showed the effect of pore morphology on corrosion resistance of sinters.

Abstract: The microstructure and chemical composition of MC carbides in the modified variants of AISI M2 type high-speed steel after casting, annealing, carburising and subsequent final heat treatment (quenching and tempering) have been studied by focusing on diffusion processes in these carbides and their stability during high-temperature treatments. Significant changes in both the microstructure and chemical composition of the MC carbides as well as in their volume fraction shown to occur in the high-speed steels studied were attributed to decomposition, coagulation and dissolution of these carbides during heat treatments caused by strong diffusion of alloying elements and carbon. It was also shown that boron, in general, strongly suppressed the diffusion of carbon during carburising.