Infrared normal spectral emissivity of Ti–6Al–4V alloy in the 500–1150 K temperature range

Abstract

Thermal radiative emissivity is related to the optical and electrical properties of materials, and it is a key parameter required in a large number of industrial applications. In the case of Ti–6Al–4V, spectral emissivity experimental data are not available for the range of temperatures between 400 and 1200K, where almost all industrial applications take place. The experimental results in this paper show that the normal spectral emissivity decreases with wavelength from a value of about 0.35 at 2.5μm to about 0.10 at 22μm. At the same time, the spectral emissivity shows a slight linear increase with temperature between 500 and 1150K, with approximately the same slope for all wavelengths. Additionally, the influence of the samples thermal history on the emissivity is studied. A strong decrease in the emissivity values appears due to the effect of surface stress relaxation processes. This means that the radiative properties of this alloy strongly depend on the surface stress state. A thermal treatment to relieve the surface stress should be carried out to achieve a steady state of the radiative properties. In addition, a good qualitative agreement is found between the temperature dependence of the electrical resistivity obtained using conventional measurements and the one obtained from the emissivity experimental results by using the Hagen–Rubens equation.