Defect and Diffusion Forum Vols. 258-260

Abstract: In this study, it will be investigated the diffusion of critical elements, namely, carbon (C) and iron (Fe), into a steel substrate (Impax Supreme) during the diamond chemical vapour deposition (CVD) process. The substrate temperature was varied from 700 to 850°C by plasma power manipulations to enable the correlation of substrate temperature with diffusion length and depth of the above mentioned critical elements into steel during film growth conditions. Methane concentration is also a parameter which has been considered during the parametric analysis. The crystalline compounds formed during the diamond growth process are studied using XRD analysis. In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements during the process. The results obtained enabled to improve traditional understanding about the mechanisms relating to diamond deposition on steel substrates using CVD processes.

Abstract: In this work a study on the structural phase transitions of silicon undergone by two different methods were performed. The samples were submitted to high non-hydrostatic pressure applied by cyclic Vickers indentations and by the tool tip during the single point diamond turning. The indentations were performed on virgin surface (polished as received) and on an amorphous surface generated either by the machining process or RF sputtering. The analysis on the machined surface, debris on the diamond tool and around of imprints were also performed using Raman micro spectroscopy. The results indicated the formation of some phases may depend upon the initial structural state of the surface, i.e., amorphous or crystalline.

Abstract: Several analytical models have been developed through the years to describe the formation and growth of the internal oxidation layer in binary alloys. Such models are often complex and their validity strongly rely on precise measurements of molar fluxes of the different species involved in the oxidation process. The main disadvantage of such measurements is that they are difficult to made and present a high degree of uncertainties, thus some assumptions are needed to ease understanding and the applicability of them. In this paper we set up a numerical scheme (finite differences) to describe the growth of the internal oxidation layer in binary Cu-Al alloys oxidized in air at different temperatures. There is good agreement between the experimental results and the values calculated with the aid of our numerical approach.

Abstract: The rate of reduction of chromium oxides in a stainless steel slag was studied in stagnant slag / metal melts at 1600 °C. The experimental results show that the magnesium contained in a FeMgSi ferroalloy has a reduction potential comparable to that of the silicon in a FeSi ferroalloy. On the other hand, it was confirmed that the rate limiting step in the reduction of the chromium oxides is the transport of chromium from the bulk of the slag to the slag / metal interface. The mass transfer coefficients for the reduction of chromium were estimated and are in good agreement with previously reported values.

Abstract: The reactive diffusion and phase formation sequences in two types of ‘internal tin’ superconducting wires designed for the ITER project, which investigates the production of electricity by means of nuclear fusion, have been studied during heat treatments both in situ, using electrical resistometry [1] and ex situ, using optical and scanning electron microscopy, energy dispersive X-ray spectrometry (EDS) and X-ray Micro-Tomography (XMT). XMT reveals long pores in the longitudinal direction which may result in tin deficiency thereat and hence local off-stoichiometric Nb3Sn. Microscopy suggests there are incomplete conversion of elemental tin to copper-tin intermetallics before ramping above the tin melting temperature, nonuniform distribution of tin before formation of Nb3Sn, and filament movement and bridging, stacking cracks and unreacted niobium at the end of the heat treatment. FEGSEM shows a fine microstructure which nevertheless could still be improved.

Abstract: The structure and properties of in situ Cu-Nb composites have been studied by the methods of TEM and SEM, X-ray analysis and mechanical testing. The evolution of Nb filaments structure at drawing and the effect of annealing and doping with Zr on the composites structure and texture have been investigated. Sharp fibre texture with <110>Nb develops in the ribbon-shaped Nb filaments, while the Cu matrix possesses a two-component fibre texture, <111>Cu and <100>Cu, appreciably affected by annealing. Annealing results in softening due to Nb filaments coagulation. In Zr doped composites two types of ZrO2 particles are observed, dispersed and coarse ones. The former result in the dispersion strengthening, while the latter may cause embrittlement.

Abstract: Binary mutual diffusion coefficients have been measured for aqueous solutions of some carbohydrates (glucose, fructose, lactose, sucrose, α-cyclodextrin and β- cyclodextrin) at concentrations from 0.002 mol dm-3 to 0.010 mol dm-3. The concentration dependence of the diffusion coefficients at physiological temperature, 37 °C, is discussed on the basis of their structures.

Abstract: We simulate fluid and solid Lennard-Jones argon systems via non-equilibrium molecular dynamics and study how the system behaves under an imposed temperature gradient until it reaches the stationary state, from where the thermal conductivity is calculated. We show that transient pressure waves propagate in the system giving rise to a density oscillation pattern. Based on the damping of this pattern we estimate the time needed to reach the stationary state. We also show that thermal conductivity is size independent in the fluid phase, while it increases until the Casimir limit in the solid phase.

Abstract: The iron and zinc calcium oxysulfides Ca3Fe4S3O6, CaFeSO and CaZnSO are synthesized by reacting mixtures of CaO and FeS or of CaO and ZnS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by X-ray microanalysis and X-ray diffraction. From the temperature-dependent lattice parameters of oxysulfides (measured up to 1170K) their thermal expansion coefficients are evaluated. Oxidation Ca3Fe4S3O6 and CaZnSO are studied by thermogravimetric analysis when air heated. Oxidation speed temperature coefficients showing that process limiting stage is diffusion are determined.

Abstract: The electrochemical permeation technique was used to evaluate the hydrogen diffusion, and analyse its interdependent solubility and trapping behaviour in 9 austenitic stainless steels. The hydrogen diffusion of all alloys obeyed Arrhenius relationships in the temperature range between 25 °C to 100 °C. The apparent diffusion coefficients were determined and the relevant activation energies were estimated. It was observed that Ni, Mo, Mn and N, among other alloying elements, clearly effect the hydrogen diffusion.