Peter N. Quested

Reference Data for the Density and Viscosity of Liquid Aluminum and Liquid Iron

The available experimental data for the density and viscosity of liquid aluminum and iron have been critically examined with the intention of establishing a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The proposed standard reference correlations for the density of the aluminum and iron are characterized by standard deviations of 0.65% and 0.77% at the 95% confidence level, respectively. The overall uncertainty in the absolute values of the density is estimated to be one of ±0.7% for aluminum and 0.8% for iron, which is worse than that of the most optimistic claims but recognizes the unexplained discrepancies between different methods. The standard reference correlations for the viscosity of aluminum and iron are characterized by standard deviations of 13.7% and 5.7% at the 95% confidence level, respectively. The uncertainty in the absolute values of the viscosity of the two metals is thought to be no larger than the scatter between measurements made with different techniques and so can be said to be ±14% in the case of aluminum and ±6% in the case of iron.

Towards high accuracy calibration of electron backscatter diffraction systems

For precise orientation and strain measurements, advanced Electron Backscatter Diffraction (EBSD) techniques require both accurate calibration and reproducible measurement of the system geometry. In many cases the pattern centre (PC) needs to be determined to sub-pixel accuracy. The mechanical insertion/retraction, through the Scanning Electron Microscope (SEM) chamber wall, of the electron sensitive part of modern EBSD detectors also causes alignment and positioning problems and requires frequent monitoring of the PC. Optical alignment and lens distortion issues within the scintillator, lens and charge-coupled device (CCD) camera combination of an EBSD detector need accurate measurement for each individual EBSD system. This paper highlights and quantifies these issues and demonstrates the determination of the pattern centre using a novel shadow-casting technique with a precision of ∼10μm or ∼1/3 CCD pixel.

The physical properties of alloys in the liquid and “mushy” states

Data on the physical properties of alloys at high temperatures are urgently needed for the mathematical modeling of high-temperature processes such as casting, welding, secondary refining, dip melting, spray forming, and metal powder production. Data are required for those properties which are involved in heat and fluid flow in high-temperature processes. Levitated drop methods have been adopted to measure the surface tensions, densities, and enthalpies of commercial alloys, and rapid, transient methods have been developed to measure thermal conductivities to avoid the problem of convection. The results obtained for the properties of commercial alloys for the liquid and “mushy” states are discussed.

Viscosity measurement of liquid ternary Cu–Ni–Fe alloys by an oscillating cup viscometer and comparison with models

Abstract Viscosity data on Cu – Ni – Fe have been obtained using an oscillating cup viscometer. In this method, a liquid sample is suspended in a crucible which performs damped angular oscillations. Viscosities are calculated from the time period and the decay of the amplitude. The temperature dependence of the measured viscosities can be described by an exponential Arrhenius law, taking into account an activation energy for the viscous flow. The activation energies for the ternary alloys were found to be linear combinations of the corresponding activation energies of the pure elements Cu, Ni, and Fe. At constant temperature, a non ideal mixing behaviour was observed and the data were compared with several quantitative models. Close agreement of the experimental results was found with the predictions of two models by Kaptay and Hirai.

Physical property measurements for the mathematical modeling of fluid flow in solidification processes

Measurement methods are being developed to provide values for the density, viscosity, heat capacity, enthalpy, fraction solid, surface tension, and thermal diffusivity and conductivity of commercial alloys in the liquid and mushy states. These data are needed for the mathematical modeling of heat and fluid flow in solidification processes. This paper briefly describes the present state of development of apparatus for the measurement of density by the levitated drop and hydrostatic probe methods and viscosity by the oscillating viscometer in our laboratory.

Surface tension and viscosity of industrial alloys from parabolic flight experiments — Results of theThermoLab project

The surface tension and the viscosity of a series of industrial alloys have been measured by the oscillating drop technique with an electromagnetic levitation device under reduced gravity conditions in several parabolic flights. It was demonstrated that the 20 seconds of reduced gravity available in a parabola were sufficient for melting, heating into the liquid phase, and cooling to solidification of typically 7 mm diameter metallic specimen. The surface tension and the viscosity were obtained from the frequency and the damping time constant of the oscillation which were evaluated from the temperature signal of a highresolution pyrometer. Alloys processed included steels, Ni-based superalloys, and Ti-alloys which were supplied by industrial partners to the project. Three to four parabolas were sufficient to obtain the surface tension and the viscosity over a large range in temperature.

Recent developments in two fundamental aspects of electron backscatter diffraction

Two very different aspects of electron backscatter diffraction (EBSD) are considered in this paper. Firstly, the use of the technique for the measurement of grain size is discussed with particular reference to the development of international standards to help ensure reproducible and repeatable measurements. In particular the lessons learnt for both calibration of the complete SEM-EBSD system and in choice of the correct data acquisition and processing parameters from an international round robin are summarized. Secondly, extending the capability of EBSD through development of new detectors is discussed. New shadow casting methods provide a means to achieve better accuracy in definition of sample-pattern geometry, while increased detail can be obtained by larger cameras and ultimately direct electron detection.

Prediction of Properties of Metals Relevant to Process Simulation

Abstract Industrial metal processes, such as casting, primary production and welding are frequently simulated using physical models which require alloy properties including liquidus and solidus temperatures and fraction solid; properties associated with heat flow: enthalpy, heat capacity and thermal conductivity and properties associated with fluid flow: density, surface tension and viscosity. These properties are required both as a function of temperature and composition. In recent years, significant developments in the experimental methods for measuring these properties have occurred, but their measurement still remains difficult and expensive. These constraints have driven the development of methods for the prediction of the properties based upon the chemical composition of the alloy. The paper describes a software program to predict properties of alloys based upon their chemical composition. The properties included are enthalpy, enthalpy of fusion, heat capacity, density, volume, fraction solid during solidification, solidification range, thermal conductivity, phases formed during solidification and viscosity. Most of the underlying models are based upon thermodynamic calculations using MTDATA, a software tool for the calculation of thermodynamics and phase equilibria developed at NPL. Transport properties such as thermal conductivity and viscosity are difficult to model and for example, thermal conductivity is estimated using empirical relationships. The program has been deliberately designed for the engineer who is not expert in thermophysical properties. The predictions will be compared with measurements for selected alloys.