Defect and Diffusion Forum Vols. 297-301

Abstract: The kinetics of intermetallic growth in the bulk, along the surface and grain boundaries (GBs) was studied in the Cd-Ni, Cd-Cu and Cu-Sn systems. Bulk dynamic diffusion coefficients exceed by a few orders of magnitudes the tracer self-diffusion coefficients in homogeneous phases. The reasons for this difference are discussed in terms of departure of growing intermetallics from stoichiometry due to the simultaneous existence of two processes: interdiffusion through the growing phase layer and chemical reactions at interfaces. Accelerating contribution of GBs and free surfaces, as fast diffusion paths, into diffusion penetrability of growing intermetallics has been investigated. It was found that the rates of lateral phase spreading along free surfaces and GBs exceed several times the rate of phase growth in the bulk. Accelerating GB contribution depends on the grain size. Nano-dispersed thin films demonstrate maximal phase propagation rates, which several times exceed even the rates of lateral phase spreading along free surfaces in coarse-grained polycrystals.

Abstract: This paper presents the results of investigations on gas nitrided austenitic stainless steel. The treatment was conducted at various temperatures (400-515°C), gas compositions of atmospheres used (20-100% NH3) and times (0.5-12h). The layers were investigated by X-ray diffraction, Light and Electron Microscopy and Glow Discharge Optical Spectrometry. The kinetics of layer growth has been analysed in terms of the process parameters and compared with the data presented for plasma treated steel. The specific nitrogen profiles of nitrided layers are discussed in the context of the layers’ microstructure and phase composition.

Abstract: In this paper, sodium bentonite (BT) and organically modified sodium bentonite (OBT) are used to reinforce and modify asphalt binder. The microstructures of the reinforced asphalt binders are investigated using transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Two models for the microstructure of the BT and OBT modified asphalts are suggested considering the colloidal structure of the base asphalt binder. The physical properties of the modified asphalt binders were studied.

Abstract: In this work, the mixed convention of air inside a rectangular cavity with moving cold sidewalls is studied numerically. A constant flux heat source is attached to the bottom wall of the cavity. A thin thermal shield is located at a specific distance above the heat source. The governing equations are solved using appropriate numerical methods. A parametric study has been conducted and the effects of heat source length, its location and the shield distance from the source on the heat transfer have been investigated. The results show that the heat dissipation increases as the heat source and the shield are moved up to a certain distance towards either sidewall. However, moving them beyond this limiting distance results in the reduction of heat dissipation. It is shown that the presence of shield results in the reduction of the heat transfer coefficient. However, for the normalized distance of the shield from the heat source greater than , the shield’s effect on the reduction of the heat transfer coefficient is less than.

Abstract: Interest in Al alloys for ship construction has increased because of the advantages of high speed with lightweight, increased load capacity, and ease of recycling compared to fiber-reinforced plastic. This study determined that the optimum traveling and rotation speeds for friction stir welding of 5052-O and 6061-T6 Al alloys for shipbuilding applications are 61 mm/min and 1600 RPM, respectively.

Abstract: Austenitic stainless steels have problem such as pitting, intergranular corrosion and stress corrosion cracking, which causes severe damage of structure in spite of high toughness and mechanical strength. To minimize these disadvantages in offshore structures demand of STS 316L which has small amount of C and has Mo is increasing. In this paper, the electrochemical experiments are executed to evaluate the durability at various protection potentials on stress corrosion cracking and hydrogen embrittlement of STS 316L in natural sea water environment. The polarization trend for STS 316L shows the effects of concentration polarization due to dissolved oxygen reduction reaction and activation polarization due to hydrogen gas generation. The turning point of two reactions in the polarization curve presented -0.92 V (vs. Ag/AgCl). The lowest current densities in the potentostatic test and non-correded surface condition of specimens by SEM analysis presented at potentials of 0 ~ -0.9 V and 0.4 ~ -0.9 V, respectively. Synthetically, the optimum corrosion protection range without stress corrosion cracking and hydrogen embrittlement is concluded with the potential range of -0.56 V ~ -0.92 V.

Abstract: The phase formation in oxide-sulphidic systems was studied with the use of X-ray diffraction, mineralography, combined thermogravimetry and calorimetry, in addition to Х-ray spectral microanalysis. The purpose of this work was to estimate the effect of cooling rate of melts in FeOx-SiO2-Cu2O-ZnO-FeS systems on structure and content of the resulting phases. Test subjects were two samples having following compositions (wt. %): I - 40.5 Fe, 2.41 S, 0.87 Cu, 3.87 Zn, 32.1 SiO2 and II - 40.7 Fe, 3.05 S, 8.55 Cu, 4.1 Zn and 19.5 SiO2. Cooling rate of the melts was changed from 0.3 up to 900оС/s.

Abstract: Heat treatable aluminium alloys show their best properties when properly heat treated. Most of the high-strength alloys are usually serviced in the so-called T6 temper consisting of ageing at moderate temperature after a solution treatment and a subsequent quenching. A large extrusion was investigated in this paper. The part was solution annealed at 505°C, water quenched and aged at 160°C for 16 hours. Each stage of the heat treatment is analyzed in this paper in the light of the properties achieved, by experimental investigations and several kinds of numerical simulations. In particular, a thermodynamic calculation (Pandat® software) provides solidification temperatures and equilibrium phases, in order to check whether the solution temperature is adequate. A finite element analysis (performed with COMSOL Multiphysics® software) supplies a simulation of the temperature field during water quenching. The cooling curves obtained are drawn on CCT (Continuous Cooling Transformation) curves, calculated by means of JMatPro® software, to verify if any undesired high temperature precipitation could occur during quenching. Finally, calculated TTT (Time Temperature Transformation) curves can be related to the ageing treatment.Thermal analyses, microstructural investigations and microhardness profile measurements on extrusion sections are also performed to validate calculated results.

Abstract: In this work the influence of thermal effects on the performance of a finite porous journal bearing has been investigated using a thermo-hydrodynamic analysis. The Reynolds equation of thin viscous films is modified taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The governing equations were solved numerically using the finite difference approach. Obtained result show a reduction in the performance of journal bearings when the thermal effects are accounted for and, this reduction is greater when the load capacity is significant.

Abstract: This paper describes a novel technique to determine mass diffusion coefficients of multi-component system within a transparent mixture by using an optical system. The mixture is composed of sodium chloride and lysozyme as solutes. Binary and multi-component solution experiments were conducted separately under constant temperature conditions. By measuring transient diffusion fields inside the cell, as well as for mixed multi-component solutions, it was confirmed that within the concentration ranges considered in this study, the diffusion of each solute inside the cell progresses independently. This indicates the superposition principle of concentration for certain levels of sodium chloride and lysozyme within the cell. Furthermore, by using this concentration superposition principle and an inverse analysis based on the conjugate gradient method, the diffusion coefficients of each solute in the mixture were successfully obtained from several multi-component experiments. Each obtained diffusion coefficient was good agreement with the determined diffusion coefficient from binary experiment.