Thermophysical Properties of Molten Metals

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  Diffraction User Center
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  Oak Ridge National Laboratory

Staff

    Wallace Porter and Ralph Dinwiddie, ORNL

Background

Recent advances in the area of solidification modeling have brought these techniques to the point where it is very advantageous to be able to use a model to simulate and optimize processes such as casting, welding , and semi-solid forming. However, it has been recognized and documented in sources such as ASM International's Advanced Materials and Processes and A Vision of the Future of the U. S. Metalcasting Industry that there is a lack of thermophysical property data for metals near and extending into the molten region. Advances in the area of process modeling are limited by this shortage of data. Depending on the process, today's modelers and designers require many thermophysical properties as a function of temperature including those listed in the Table below.
Thermophysical Properties Required by Solidification Models
density thermal expansion
specific heat capacity heat of fusion
thermal diffusivity thermal conductivity
melting temperature emissivity
viscosity surface tension

Approach

  • Identify properties that could be measured using existing Thermophysical Properties User Center(TPUC) instruments at the HTML
  • Include capability to measure molten materials in specifications for new TPUC instruments
  • Design special molten metal specimen containers and develop the techniques required to use them in existing TPUC instruments
  • Identify the techniques / instruments required to measure any remaining properties


The high temperature Differential Scanning Calorimeter(DSC) has a range of RT-1500oC and can measure liquidus and solidus temperatures, heat of fusion, and specific heat capacity.

The DSC was used to determine the fractional heat of fusion of Ni-Al bronze.

The high temperature dilatometer has a range of RT to 1600oC. Special specimen containers have been designed and fabricated which allow the measurement of the density and thermal expansion of molten metals.

Density of Al-Si Alloy 356 as a function of temperature.

Inset shows specimen and graphite container used for the measurement.

When HTML's Laser Flash Thermal Diffusivity(LFTD) system was recently replaced, the capability to measure molten metals was included in the specification. The new LFTD has a range of -150 to 2500oC. The thermal diffusivity of molten metals can be measured up to 1700oC using special specimen containers designed by TPUC staff.

Thermal diffusivity of HY 100 steel as a function of temperature.

Inset shows specimen and container used for the measurement. The container consists of sapphire windows, an alumina spacer ring around the specimen, and graphite housing and lid.

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Acknowledgments

URL: http://www.html.ornl.gov/tpuc/molten.html