Advanced Materials Research Vols. 15-17

Abstract: Strip casting is a promising route to directly produce magnesium alloy sheet by twin roll casting method. As-cast strips with proper microstructure and good surface quality are requested to serve as next rolling feedstock. In order to restrain the coarse dendrite growth and get uniform grain, a new method of in-line heat treatment was proposed. The as-cast strip was dipped into an oil tank after exiting the rolls and then was quenched with oil at various temperatures. The effect of oil temperature, casting speed and pouring temperature on microstructure and mechanical properties of cast strip was investigated.

Abstract: Biphasic calcium phosphate (BCP) bioceramics, for use as resorbable bone substitutes, containing both isolated macropores and interconnected micropores, have been fabricated by sintering, using naphtalen particles as a porogen to produce macropores. The resulting ceramics contain ~ 45% macropores and various amounts of microporosity. Mechanical properties (compression and bending strength, toughness and hardness) have been measured and modeled by combining two approaches, at two different scales: the one describes the mechanical properties of a partly sintered stacking of grains, supposed to account for the interconnected microporosity, the other one holds in the case of closed and isolated macropores within a continuous matrix. The material is then represented as a quasi-continuous matrix containing macropores, the matrix being itself microporous. The model also considers that fracture always initiates on a macropore, which allows to set a correspondence between fracture toughness and fracture stress equations. The mechanical tests performed on the sintered ceramics tend to validate the modeling approach.

Abstract: Induction heating is a case hardening process used to improve performance of machine components by producing a hard martensitic microstructure and high compressive residual stresses at the surface layer. A reliable numerical model able to predict the hardness profile would shorten process development. However, the accuracy and the efficiency of the model are restricted by the coupling complexity between the electromagnetic and thermal fields, and the nonlinear behaviour of the material properties. The paper analyzes the sensitivity of the material properties values and of the finite element meshing onto the predictive modeling of the case hardening profiles. The material used is SAE-4340 low-alloy steel. The simulations are done using a computer-modeling software (Comsol) and the sensitivity analysis is conducted by using an experimental design method.

Abstract: High molybdenum high strength stainless steels can contain the so-called Chi phase (Fe36Cr12Mo10). The presence of this phase, which normally occurs at grain boundaries, depletes the chromium content leading to intergranular corrosion. This may cause alloy embrittlement during long term use. The presence of such phase has proven to be highly sensitive to alloy processing parameters such as the cooling rate after a final heat treatment. The present work provides a model to quantify the effects of processing parameters aimed at controlling the Chi phase. The model is based on nucleation and growth classical theories involving capillarity effects for the early stages; it is applied to a range of heat treatment conditions and compared to experimental results.

Abstract: Of all the processing stages for wafers, interior temperature distribution in thermal treatment furnaces has a great influence on wafer properties. Therefore, internal temperature distribution is a key factor for operating a furnace. However, it is practically impossible to directly measure temperatures within the furnace, and consequently the need for a reliable numerical model to analyze temperature distribution is becoming increasingly urgent. Exact modeling of the processing is very difficult because the structure of the furnace used for thermal treatment is very complex, with large numbers of Si wafers stacked within. Therefore, simplified modeling is necessary. The modeling strategy of the present study is to reduce the radiation calculation domain and simplify the model by replacing the wafer stack region with a single block. It is necessary to determine the vertical and horizontal effective thermal conductivities of the block to reflect radiation heat transfer between wafers. In this study, calculations were performed through numerical experimentation, using r k as the heat transfer coefficient in the direction of the radius, and v k for the vertical direction. Using these calculated property values, the temperature distribution within a 300mm thermal treatment furnace can be obtained.

Abstract: We developed a synthesis method of nanomaterials by the impulse plasma in liquid. The method is based on the low voltage pulsed plasma. The apparatus is very simple and does not require vacuum system, high-energy, cooling system, but can evaporate even refractory metals. Preparation experiments of nanomaterials by using Impulse Plasma in Liquid method were performed. We succeeded in synthesis of nanocrystals of some metals, TiO2, and fullerene C60. The synthesized TiO2 powder consists of fine-dispersed particles of rutile and anatase phases with 5-15 nm grain size. Pure fullerene C60 was prepared by dispersion of graphite electrodes by Impulse Plasma in toluene. It was suggested that the present method can be effectively used for nanomaterials preparation.

Abstract: Ptx-Pd(1-x) nanoparticles supported on amorphous silica (SiO2) were prepared by wetness impregnation techniques with choroplatinic acid (H2PtCl6) and palladium chloride (PdCl4) with different concentrations of Pt and Pd at about 1% in overall metallic weight. The purpose of this study was to evaluate the physical properties as physisorption (BET), X Ray Diffraction XRD, High Resolution Electron Microscopy HREM, Transmission Electron Microscopy TEM couple with XEDS energy dispersive X-ray spectrometry and chemical properties to determine the activity in cyclohexene reaction of these materials supported. Bimetallic nanoparticles are made of a single solid solution of Pt and Pd atoms, and the particles diameter of about 3-5 nm was estimated by HREM and Bright field image, the Pt-Pd nanoparticles were found mainly to have truncated cuboctahedral shape with fcc packing,. by using energy dispersive X-ray spectrometry (XEDS) and their values were found to be close to the stochiometric relative concentrations in weight of the metals in the precursor aqueous solution.