Thermophysical property requirements for modelling of high temperature processes

Mathematical modelling is recognised as a valuable tool to improve process control and product quality. These models have developed to the stage where reliable thermophysical property data for the materials involved in the process is now one of the prime requirements to improve accuracy. Thermophysical property data are needed to model the heat and fluid flow in casting and foundry operations, welding, secondary refining, dip coating, etc... Data are needed for the following properties: density; viscosity; surface tension; specific heat capacity; enthalpy; thermal and electrical conductivity; emissivity; and fraction solid in the mushy region. These data are needed for a wide range of alloys. including steels, aluminium alloys, and titanium- and nickel-based alloys. Using simulations of the solidification of aluminium alloys in shape castings as an example, it is illustrated how the introduction of accurate thermophysical data significantly improved the prediction of defects. The simulations can also be used to determine which properties are the most critical for accurate predictions; therefore, sensitivity studies can be performed to focus measurement efforts. Accurate thermophysical property data are frequently difficult to obtain at high temperatures, especially for reactive alloys such as titanium and nickel based superalloys. Additionally, other problems, such as the effect of convection on thermal conductivity and on diffusivity, hampers experimentalists. These problems are outlined, focussing on the usefulness of microgravity experiments which allow reference data to be obtained and ultimately improve data for industrial alloys.