Defect and Diffusion Forum Vols. 273-276

Abstract: Grain boundary and surface tension for pure copper and copper-based alloys with Sb, Sn and In are measured by zero creep method. On the base of these and literature data, using the Shyshkovsky equation for a dilute solution, the isothermes of surface tension and grain boundary tension are constructed in Cu-based alloys with Sb, Sn, In and also Bi and Au. It is shown that all solutes are active on the surface tension of copper. The free energies of adsorption are negative and decrease in a following consequence: Bi, Sb, Sn, In, and Au.

Abstract: Generation of vapor and predication of its behavior is an important problem in many industries. In this study, the three dimensional governing equations for turbulence two-phase flow are derived using ensemble averaging two fluid model. The governing equations are simplified by a heuristic approach based on boiling data, and the equations are used to obtain the parameters for each phase along the channel. A computer program is written for the simplified one-dimensional equations, and the results are compared with experimental data.

Abstract: The study of mechanical alloying on the Fe–Cu system, as a model system for those with positive heats of mixing, are investigated. In this research work the effects of impact force, such as increasing in the surface temperature of powders, the number of vacancies and pipe diffusion, on the strain and grain size of final powders have been studied. The aim of this research is to find the optimum condition for mechanical alloying of Cu-Fe system by the help of automatic design and analysis of TAGUCHI experiments.

Abstract: Current researches show a growing interest in Zinc Oxide (ZnO) nanoparticles. ZnO is a semiconductor with a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. Several methods have been developed in order to synthesize ZnO nanoparticles. Chemical methods, among them sol-gel process, are more convenient. Sol-gel is common for producing metal oxide nanoparticles because of its simplicity, cheapness and high quality products. In this research ZnO nanoparticles were prepared via the sol-gel process. ZnAc2.2H2O as precursor and TEA (Triethanolamine) as a novel surfactant were used in a methanolic solution. MEA (Monoethanolamine) and DEA (Diethanolamine) have been highly used before. In this research, solutions with different weight ratios of ZnAc to TEA (1:2, 1:1 and 2:1) were obtained. After drying, all samples were calcinated at 500 °C for 1 hr. Obtained nanoparticles were characterized with the hope of achieving better properties.

Abstract: The interaction between manganese(II) oxide and carbon in powder mixtures may give manganese carbides, condensed(c) and gaseous(g) manganese at different temperatures and pressures. The initial assumptions and results of thermodynamic modelling of this interaction in the temperature range 1600-2100 K at the pressures 0.1-1.0 MPa are presented in this paper.

Abstract: Average ternary interdiffusion coefficients in Ni3Al with Ir additions have been determined using solid-to-solid diffusion couples annealed at 1200°C for 5 hours. Disc shaped alloy specimens were prepared by the vacuum arc melting at compositions of Ni-24Al, Ni-25Al, Ni-26Al, Ni-23.5Al-1Ir, Ni-24.5Al-1Ir, Ni-23Al-2Ir, Ni-23Al-2Ir, Ni-24Al-2Ir, Ni-23Al-3Ir (at.%). Surfaces of alloys were polished down to 1200 grit and diffusion couples were assembled in Si3N4 jig for initial bonding heat treatment at 1200°C for 0.5 hours. Additional diffusion anneal was carried out at 1200°C for 4.5 hours outside of Si3N4 jig so that diffusion couples can be water quenched. Concentration profiles of individual components were measured by electron probe microanalysis using pure standard of Ni, Al and Ir. Interdiffusion flux of individual component was determined directly from the experimental concentration profiles, and the moments of interdiffusion flux were examined to calculate the average ternary interdiffusion coefficients, D˜ ij k either with Al or Ni as dependent component. Calculated interdiffusion coefficients suggest that Ir-alloyed Al2O3-forming oxidation resistant coatings would be beneficial to reduce the interdiffusion flux of Ni from superalloy substrates to the coating, and reduce the interdiffusion flux of Al from the coating to the superalloy substrate.

Abstract: In studying grain boundary segregation in Cu–Bi alloys by means of Auger electron spectroscopy samples must be broken in-situ. Consequently, the distribution of segregants on both sides of fracture path must be considered quantitatively. This question can be addressed by studying the influence of an adsorbed oxygen layer on the intensity of Auger peaks. This oxygen layer forms on the fracture surface when it is intentionally exposed to air. In this work, the values of Bi coverage have been measured both on the as-fractured Cu fracture surface and on the fracture exposed to air. The coverage values evaluated from the model of a crosstie-like pattern agree better with each other than those from the model of a continuous layer. Our study reveals that the Cu-Bi bond is weaker than the Bi-Bi bond.

Abstract: The wetting behavior of grain boundaries is affected by temperature, pressure and misorientation of grain boundaries. However, the influence of quenching baths on liquid state grain boundary wetting is rarely reported. In this work, this effect in the Sn−25 at% In alloy was investigated. The Sn−In alloy was prepared by smelting of In and Sn at 300°C for 6 hr in Ar atmosphere. Samples were annealed at temperature between 130 and 165°C and quenched in two kinds of baths: −10°C salt-saturated water and liquid nitrogen. The results from X-ray diffraction show a difference in preferential orientations between samples quenched in these two baths. Metallographic analysis reveals that the percentage of grain boundaries fully wetted in samples quenched in −10°C salt-saturated water is lower than that quenched in liquid nitrogen. It is pointed out that a proper quenching bath is necessary for preserving the initial microstructure of grain boundary wetting.

Abstract: An oxide scale layer always forms at the strip surface during the hot rolling process. As a consequence, de-scaling and pickling operations must be performed prior or after hot rolling. Many surface defects caused by hot rolling are related to oxidation in the reheating furnace. One of these is the melting of eutectic FeO/Fe2SiO4 during reheating over 1170°C giving as a result red scale defects in Si-added steel. On the other hand, steel strip surface oxidation during hot rolling causes an industrial and environmental problem: secondary oxide is removed after roughing, but tertiary oxide scales already start to form before entering the finishing stands. Their properties affect the final steel surface quality and its response to further processing. Furthermore, the addition of alloying elements has an important impact on scale properties. In particular the alloying of silicon effects the region between scale and substrate. It causes peculiar surface properties inherited from its specific oxidation characteristics. Conventional oxidation experiments in air of silicon steels are a valuable tool to study the influence of Si on steel oxidation. After oxidation in air in the temperature range of 900-1250°C it has been observed that Si enhance markedly scale adhesion, especially above 1177°C (the eutectic temperature of FeO-Fe2SiO4 ) and also at lower temperatures. Special attention has been paid on the investigation of the effects of alloying Si on the high-temperature oxidation of steel, for a better understanding of the behaviour of modern steels during hot rolling.

Abstract: Exposure of metals and alloys to high temperatures leads to the formation of oxide scales, with a large impact on surface quality. The most important features of the oxide layer are its thickness, composition, structure, adherence and coherence. Temperature, time, gas atmosphere and chemical composition determine the growth of oxide layers. In this paper, the characteristics of the high temperature oxidation properties of Fe-Si alloys are discussed in terms of oxide growth mechanism, kinetics and phase morphology. The oxidation kinetics of different Fe-Si alloy steels in air, its scale structure and composition were investigated over the temperature range 900-1250°C. Oxidation experiments were performed in air, to analyse the oxidation process. Experiments were carried out in an electric furnace at temperatures ranging from 900 to 1250°C, for times between 16 and 7200s. Thus treated specimens were characterised by metallography and their scale thickness was measured by optical microscopy. Scale morphology was studied and scale composition confirmed by EDS (Energy Dispersive Spectroscopy) and EBSD (Electron Backscattered Diffraction) analysis. Results show that high temperature oxidation of Si- alloys presents the classic three layered oxide scale. On the grain boundaries in the scale, iron-silicate was found. Observations show a Sienrichment at the scale –metal interface. This enrichment is present in the form a mixed wustite-iron silicate (fayalite) phase, FeO-Fe2SiO4. A very rapid build-up of oxide occurs when a liquid phase, due to the wustite-fayalite eutectic, is present in the surface of the steel.