Claus Cagran

Thermophysical properties of a Ti–44%Al–8%Nb–1%B alloy in the solid and molten states

Abstract The families of titanium aluminide intermetallic alloys have attractive high temperature mechanical properties which make them potential candidate materials for a wide range of applications, particularly in the aeronautic and automobile sectors. The development of appropriate manufacturing techniques is an essential stage in the engineering exploitation of these materials, e.g., Induction Skull Melting is one of the techniques which needs to be optimised for the casting of titanium aluminides. Research is underway to develop a computer model of this process but data are required for the key thermophysical properties. Pulse-heating techniques have been used to measure properties for the Ti–44Al–8Nb–1B system. Rectangular samples have been prepared and are resistively heated as part of a fast capacitor discharge circuit. Time-resolved measurements with sub-μs resolution of currents through the specimen were made with a Pearson probe current monitor using the induction principle. Voltages across the specimen were determined with knife-edge contacts and voltage dividers, and radiance temperatures of the sample were measured with a pyrometer. These measurements allow the calculation of specific heat and dependencies between enthalpy, electrical resistivity and temperature of the alloy up into the liquid phase. Data for thermal diffusivity have been obtained by using the Wiedeman–Franz relation. The results are compared with those obtained using DSC and the four-probe method to measure the temperature dependence of the resistivity.

Thermophysical Properties of Palladium

The Subsecond Thermophysics Group at Graz University of Technology has been working to determine the thermophysical properties of liquid metals for about 25 years. The work remains relevant and of current interest for scientific applications as well as for the metalworking industry. Accurate data for the melting transition and the liquid state are often sparse, but are essential inputs to computer simulations, for instance those of solidification or die-casting. Palladium is used in dentistry, jewellery, watchmaking, spark plugs, the production of electrical contacts, and metallising ceramics (1). Finely divided palladium makes a good catalyst, used to accelerate hydrogenation and dehydrogenation reactions, and for petroleum cracking. The palladium-hydrogen electrode is used in electrochemical studies. Palladium has recently attracted much interest as a potential replacement for higherpriced platinum in catalytic converters for controlling emissions from diesel vehicles. The present experiments on palladium form part of a systematic investigation of the thermophysical properties of the platinum group metals. Measurements on rhodium are scheduled in the present programme; osmium and ruthenium are not available in wire shape. Platinum and iridium have already been investigated (2–4), and show a slight increase of normal spectral emissivity at wavelength 684.5 nm in the liquid phase, similar to the trend in emissivity values for palladium reported in the present work.

Electrical resistivity of high melting metals up into the liquid phase (V, Nb, Ta, Mo, W)

Objective of the collaboration of TU Graz and DLR Cologne is the measurement of specific electrical resistivity comparing pulse-heating and levitation results. The TU Graz measurements on V, Nb, Ta, Mo and W will be presented and discussed with regard to volume expansion and resistivity.

Normal spectral emissivity near 680 nm at melting and in the liquid phase for 18 metallic elements

Optical and thermophysical properties of pure metals at the melting point and in the liquid phase are of general interest for technological applications. This is especially true for those metals that are commonly applied. Many of these elements are used either in their pure form or as alloying components. Due to their widespread use in industry an ongoing need for new and more accurate data exists. Based on an ohmic pulse-heating apparatus, properties of conducting materials can be obtained from temperatures of about 1200 K, at which most metals are in the solid state, up to about 5000 K in the liquid state. To enable a fast and accurate temperature measurement over such a vast range, pyrometric temperature detection based on Plancks radiation law is employed. Furthermore, a microsecond-resolution ellipsometric device with no moving parts, called μs-DOAP (Division-of-Amplitude-Photopolarimeter) as first described by Azzam [1], is applied to measure normal spectral emissivity close to the wavelength of the pyrometer (650 nm). In the present paper, measurements of normal spectral emissivity at 684.5 nm, obtained by means of the above-mentioned pulse-heating technique combined with a μs-DOAP, are summarized for 18 metals, namely cobalt (Co), copper (Cu), gold (Au), hafnium (Hf-3%Zr), iron (Fe), iridium (Ir), molybdenum (Mo), nickel (Ni), niobium (Nb), palladium (Pd), platinum (Pt), rhenium (Re), silver (Ag), tantalum (Ta), titanium (Ti), tungsten (W), vanadium (V) and zirconium (Zr). The results are very important in order to eliminate uncertainties arising from the unknown behavior of emissivity at melting and in the liquid phase when investigating temperature-dependent thermophysical properties.Optical and thermophysical properties of pure metals at the melting point and in the liquid phase are of general interest for technological applications. This is especially true for those metals that are commonly applied. Many of these elements are used either in their pure form or as alloying components. Due to their widespread use in industry an ongoing need for new and more accurate data exists. Based on an ohmic pulse-heating apparatus, properties of conducting materials can be obtained from temperatures of about 1200 K, at which most metals are in the solid state, up to about 5000 K in the liquid state. To enable a fast and accurate temperature measurement over such a vast range, pyrometric temperature detection based on Plancks radiation law is employed. Furthermore, a microsecond-resolution ellipsometric device with no moving parts, called μs-DOAP (Division-of-Amplitude-Photopolarimeter) as first described by Azzam [1], is applied to measure normal spectral emissivity close to the wavelength of th...

Normal Spectral Emissivity of Liquid Copper and Liquid Silver at 684.5 nm

Up to now temperature measurements on pulse‐heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity in the whole liquid phase because of the lack of data for the liquid metals. The emissivity for most metals is known at the melting point and it is also known that large changes in specific volume occur between the melting point and maximum experimental temperatures. Since electronic structures, optical properties, and emissivities have a large dependence on the electron density of a material, it follows that the emissivity of the liquid cannot be assumed to be constant and equal to the value at the melting point a priori. The key innovation which removes the ambiguity present in all previous measurements is that uncertainty in temperatures is eliminated by the direct measurement of material optical properties and emissivities for the first time during the experiments. Normal spectral emissivity measurements at 684.5 nm have been suc...