Resampling technique applied to statistics of microsegregation characterization

Characterization of chemical heterogeneities at the dendrite scale is of practical importance for understanding phase transformation either during solidification or during subsequent solid-state treatment. Spot analysis with electron probe is definitely well-suited to investigate such heterogeneities at the micron scale that is relevant for most solidified products. However, very few has been done about the statistics of experimental solute distributions gained from such analyses when they are now more and more used for validating simulation data. There are two main sources generating discrepancies between estimated and actual solute distributions in an alloy: i) data sampling with a limited number of measurements to keep analysis within a reasonable time length; and ii) uncertainty linked to the measurement process, namely the physical noise that accompanies X-ray emission. Focusing on the first of these sources, a few 2-D composition images have been generated by phase field modelling of a Mg-Al alloy. These images were then used to obtain "true" solute distributions to which to compare coarse grid analyses as generally performed with a microanalyser. Resampling, i.e. generating several distributions by grid analyses with limited number of picked-up values, was then used to get statistics of estimates of solute distribution. The discussion of the present results deals first with estimating the average solute content and then focuses on the distribution in the primary phase

Study of the Eutectoid Transformation in Nodular Cast Irons in Relation to Solidification Microsegregation

Eutectoid transformation in cast irons may proceed in the stable or the metastable systems giving ferrite and graphite for the former and pearlite for the latter. The present work demonstrates that composition profiles across ferrite/pearlite boundaries are smooth and similar to those issued from the solidification step. No trace of long-range diffusion of substitutional solutes due to austenite decomposition could be observed. In turn, this ascertains that both stable and metastable transformations proceed with the product matrix—either ferrite opearlite—inheriting the parent austenite content in substitutional solutes. This result sustains a physical model for eutectoid transformation based on the so-called local para-equilibrium which is commonly used for describing solid-state transformation in steels

Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys

Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton’s like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration

The free energy of the Potts model: from the continuous to the first-order transition region

We present a large $q$ expansion of the 2d $q$-states Potts model free energies up to order 9 in $1/\sqrt{q}$. Its analysis leads us to an ansatz which, in the first-order region, incorporates properties inferred from the known critical regime at $q=4$, and predicts, for $q>4$, the $n^{\rm th}$ energy cumulant scales as the power $(3 n /2-2)$ of the correlation length. The parameter-free energy distributions reproduce accurately, without reference to any interface effect, the numerical data obtained in a simulation for $q=10$ with lattices of linear dimensions up to L=50. The pure phase specific heats are predicted to be much larger, at $q\leq10$, than the values extracted from current finite size scaling analysis of extrema. Implications for safe numerical determinations of interface tensions are discussed.Comment: 11 pages, plain tex with 3 Postscript figures included Postscript file available by anonymous ftp://amoco.saclay.cea.fr/pubs.spht/93-022.p

Critical evaluation of the FeeNi, FeeTi and FeeNieTi alloy systems

The FeeNieTi alloy system has been evaluated, together with FeeNi and FeeTi binary subsystems, to provide reliable information for applications and in view of a thermodynamic modelling of the system. Available literature has been critically evaluated, mainly considering phase constitution and phase equilibria, thermochemical and diffusion data, as well as ab initio atomistic calculations. A discussion of the presently available CALPHAD-type thermodynamic assessments is also presented. Finally, new experimental investigations needed to solve uncertain and contradictory data are suggested

Índices sintéticos de actividad económica local. Un estudio comparado entre Bariloche y Mar del Plata (2006-2020)

El trabajo presenta un análisis comparativo entre las dinámicas de crecimiento de dos municipios con estructuras productivas fuertemente sesgadas a su oferta de recursos turísticos. El primer caso es el del Municipio de General Pueyrredon en la Provincia de Buenos Aires, cuya ciudad cabecera es Mar del Plata. El segundo caso, es el del Departamento de Bariloche, en la Provincia de Río Negro, cuya cabecera es San Carlos de Bariloche. El estudio, que se circunscribe al periodo 2006-2020, presenta y examina la evolución de los indicadores sintéticos de actividad económica disponibles para ambas jurisdicciones -ISAE-GP e ISAE-SCB, respectivamente-, de tipo coincidente y con frecuencia mensual, que capturan el comportamiento de un conjunto de variables heterogéneas vinculadas con el nivel de actividad.Fil: Malvicino, Facundo E. Universidad Nacional de Río Negro. Centro Interdisciplinario de Estudios en Territorio, Economía y Sociedad; Argentina.Fil: Lacaze, María Victoria. Universidad Nacional de Mar del Plata. Facultad de Ciencias Económicas y Sociales; Argentina

Effect of various dopant elements on primary graphite growth

Five spheroidal graphite cast irons were investigated, a usual ferritic grade and four pearlitic alloys containing Cu and doped with Sb, Sn and Ti. These alloys were remelted in a graphite crucible, leading to volatilization of the magnesium added for spheroidization and to carbon saturation of the liquid. The alloys were then cooled down and maintained at a temperature above the eutectic temperature. During this step, primary graphite could develop showing various features depending on the doping elements added. The largest effects were that of Ti which greatly reduces graphite nucleation and growth, and that of Sb which leads to rounded agglomerates instead of lamellar graphite. The samples have been investigated with secondary ion mass spectrometry to enlighten distribution of elements in primary graphite. SIMS analysis showed almost even distribution of elements, including Mg and Al (from the inoculant) in the ferritic grade, while uneven distribution was evident in all doped alloys. Investigations are going on to clarify if the uneven distribution is associated with structural defects in the graphite precipitates

Structure of smectic defect cores: an X-ray study of 8CB liquid crystal ultra-thin films

We study the structure of very thin liquid crystal films frustrated by antagonistic anchorings in the smectic phase. In a cylindrical geometry, the structure is dominated by the defects for film thicknesses smaller than 150 nm and the detailed topology of the defects cores can be revealed by x-ray diffraction. They appear to be split in half tube-shaped Rotating Grain Boundaries (RGB). We determine the RGB spatial extension and evaluate its energy per unit line. Both are significantly larger than the ones usually proposed in the literatureComment: 4 page