摘要: Medium-carbon, silicon-rich steels are commonly suggested to obtain a very fine bainitic microstructure at a low temperature slightly above Ms. Thereby, the resulted microstructure consists of slender bainitic-ferritic plates interwoven with retained austenite. The advanced strength and ductility package of this steel is much dependent on the fineness of bainitic ferrite, as well as the retained austenite phase. In this article, the aluminum to silicon ratio, and the isothermal transformation temperature have been adopted to obtain ultra-high strength high carbon steel. Optical and SEM investigation of the produced steels have been performed. XRD has been used to track the retained austenite development as a result of the change in the chemical composition of developed steels and heat treatment process. Mechanical properties in terms of hardness and microhardness of obtained phases and structure were investigated. Results show that the increment of aluminum to silicon ratio has a great effect in promoting the bainitic transformation, in tandem with improving the stability and the fineness of retained austenite. Such an advanced structure leads to enhancement in the whole mechanical properties of the high carbon steel.
摘要: In metallurgy and materials engineering, a number of phase transformation in solids like precipitation, oxidation, creep, annealing, homogenization, etc. are brought about by the process of diffusion. Many industrial manufacturing processes utilize solid-state diffusion principle, to name a few: 1. Rotating or sliding parts of steel have a hard outside case for wear resistance and a tough inner core for fracture resistance by gas carburizing procedure; 2. Integrated circuits were produced by diffusing impurity into silicon wafers; and 3. Joints between similar and dissimilar metals, alloys, and non-metals, were made using diffusion bonding (DB) technique. Day by day, the science of solid-state diffusion phenomenon is spreading inevitably into new areas of engineering and technology. Diffusion-Assisted-Joints (DAJs) meet the requirements for most critical structures in terms of strength, toughness, tightness, and resistance to heat and corrosion. DAJs can be made out of 730 pairs of dissimilar metals. Hence, DB is considered as an engineering marvel among all the physical welding metallurgists. Herein, experiments were performed to exactly map the quantum influence of the bonding temperature variation on the dissimilar joints of a popular light alloy, Ti-6Al-4V (TiA), and a heavily used heavy alloy, stainless steel (SS), using diffusion mechanism in high-vacuum environment. Cu foil (~200 μm) was used as an interlayer. Necessary characterization tools for metallurgical investigations were used to understand the extent of diffusion along the TiA/Cu and Cu/SS interfaces, room-temperature mechanical properties, fracture morphologies, and fracture path of the TiA/Cu/SS DAJs. This paper discussed rational reasons backing the results of the characterizations.
摘要: The mechanical characteristics are determined to a FeB/Fe2B coating applied in AISI L6 steel tool and blades make to cut paper. The thermochemical treatment was applied at temperatures of 1173, 1223 and 1273 K with permanence time of 0.5, 2 and 3 h for each temperature. The diffusion coefficient and activation energy for each phase is obtained for this boron coating on an AISI L6 steel. HRC test were made to establish the type of adherence (qualitative) and comparing with the VDI 3198 standard and the results were obtaining optimal classification of HF1-HF2 in condition for 3h of the three temperatures. The result by nanoidentation show hardness of 1000 - 2000 HV as well as the Young's modulus for each present phase of the coating. Through micrographs (SEM) are showing thicknesses up to 79.52 ± 18.82 μm for FeB and 97.80 ± 20.01μm for Fe2B, a morphology sawn ́s type is evidence. Through EDS and x-ray diffraction are used to show the chemical elements formed.
摘要: The structure of partly desorbed and quenched samples of MgH2 has been investigated by the neutron diffraction method. In ambient conditions a partly desorbed sample demonstrates high stability, while the same sample quenched at low temperature decomposed into Mg after several days. Obtained neutron data showed that all studied samples contain coexisting Mg and MgH2 phases. Hydrogen distribution for both quenched and non-quenched samples is similar. Hydrogen atoms occupied sites predominantly in the MgH2 lattice, whereas Mg lattice is free of the hydrogen.
摘要: A reaction-diffusion framework (RDF) is used to synthesize and control the size and morphology of single crystals of metal-organic framework-199 (MOF-199). The framework consists of diffusing copper ions (Cu2+, outer electrolyte) into a hydrogel medium containing the organic linker, 1,3,5-benzenetricarboxylic acid (BTC, inner electrolyte). The resulting supersaturation gradient, and its nonlinear coupling with nucleation and growth kinetics, provides means to control the crystal size, distrubution and morphology along the diffusion flux. This method is rapid, efficient, scalable, and environmentally friendly. By using this method we demonstrate how assorted experimental parameters, such as temperature, concentrations, and nature of the gel matrix can be easily tuned to produce different particle size distributions and various morphologies.
摘要: AISI304 stainless steel was bonded by a nickel base interlayer, using a TLP bonding method at 1150 °C with different holding times. The microstructure of the joint region was studied by optical and scanning electron microscopes. The results showed that 20 minutes holding time is sufficient for complete isothermal solidification. At the bonding times of 4, 10, 15 minutes, a eutectic structure was formed at the joint region. The distribution of alloying elements within the joint region and diffusion affected zone were detected using EDS. The results showed that the eutectic microstructure consists of Fe and Cr borides and the isothermal solidified zone consists of solid solution of Fe and Ni at the bonding temperature. Samples with complete isothermal solidified joint were homogenized at 950°C for different times from 30 to 360 minutes to study the distribution of alloying elements between joint region and parent alloy. The results showed more uniform distribution of alloying elements with increasing the homogenization time due to the diffusion of alloying elements between the joint region and the parent alloys. Microhardness and shear strength of joined samples were measured and compared to that of the parent alloy at the same heat treatment condition. The joint shear strength of TLP bonded samples was about 82% that of the parent alloy at the homogenization time of 180 minutes.
摘要: A moisture measuring device based on non-destructive method of gamma rays attenuation, allows measures to deepen concepts in building physics related to the moisture transfer; study the influence of the interface between layers in moisture transfer; analyse the influence of gravity on absorption and drying of different building materials; study the kinetics of absorption and drying of walls of one or more layers; analyse the importance of the temperature gradient in the movement of moisture; calculate the coefficient of water diffusivity of some building materials.
In this work the proposed non-destructive method of gamma ray’s attenuation was used to analyse the transport of liquid water along a constructive element. For that propose gamma ray hydric profiles with red brick samples, 2 types: “A” and “B”, were obtained. Gamma ray hydric profiles are very interesting and original considering that the equipment exists in just a scarce laboratory. It is also intended to show how the equipment works and the way that those profiles can be taken.
The water content profiles experimentally measure are very interesting, and the preliminary results obtained, for red brick samples with different densities and sectional area, will be shown and discussed.
摘要: The Resin Transfer Molding process (RTM) has been widely used for manufacturing of high performance components in aerospace and automotive industries. It is an economical and faster method when compared to open molding process because it allows the molding of complex parts with constant thickness, dimensional precision, good surface finishing and an excellent control of mechanical properties. In this sense, this work aims to study theoretically the manufacture process of polymeric composites reinforced with fibers via resin transfer molding. The governing equations of conservation of mass and momentum, and Darcy's law are presented, and the exact solution of the problems is obtained via method of separation of variables. Predicted results of the flow front and the pressure fields of the resin inside the model during the injection process are presented, compared with experimental data and analyzed. It was verified a good agreement between the results.
摘要: Vegetable fibers have been used in most several applications, as raw material, for manufacturing of different products or directly as reinforcement in composite materials. Green fibers are wet, what requires its drying before their use.In this sense, the aim of this work is to study drying of the sisal fibers in oven. Drying experiments were carried out at different drying condition. It was evaluated the curves of moisture content, drying and heating rates and temperature, as well as the influence of the drying temperature on the mechanical properties of the fibers. It was found that the drying temperature (60 - 105°C) had no significant influence on the tensile mechanical properties, elongation at rupture and modulus of elasticity of the sisal fibers.