Thermophysical properties reference data for some key engineering alloys

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A summary is given of the results of various NPL measurements carried out over a number of years on specimens of 310 and 430 stainless steel, Inconel 600, and Nimonic 75 alloys. The properties measured were thermal conductivity, λ, thermal diffusivity, a, specific heat capacity, C p , and electric resistivity, p. Linear thermal expansivity values are also included to allow corrections to be made to the results of thermal measurements, including density, due to dimensional changes that occur on heating. Definitive NPL values are presented for selected thermophysical properties for three key engineering alloys, over the temperature ranges from ambient to 750 °C and for one alloy up to 500 °C. In addition comparisons are made between the measured thermal conductivity values and those obtained indirectly from measurements of (i) thermal diffusivity, specific heat capacity, and density; and (ii) electric resistivity via the Wiedemann-Franz relationship. This comparison study is important, as thermal conductivity is often calculated when direct measurements are either not available or not possible. Overall, the average of the measured values of thermal conductivity and those calculated via measurement of electric resistivity agree to within 4%; and those calculated via measurements of thermal diffusivity, specific heat capacity, and density are in good to moderate agreement within 10%. For austenitic and ferrite steels and nickel-chromium alloys, calculation of thermal conductivity via electric resistivity has proved to be reliable and convenient and its use can be recommended. The derivation of thermal conductivity from thermal diffusivity is reliable, except at temperatures where phase changes occur.