Effect of the surface oxidization and nitridation on the normal spectral emissivity of titanium alloys Ti–6Al–4V at 800–1100 K at a wavelength of 1.5 μm

Abstract

This work strived to model the effect of surface oxidization and nitridation on the normal spectral emissivity of Ti–6Al–4V alloys at a temperature range of 800–1100K and a wavelength of 1.5μm. In experiments, the detector was as close to perpendicular to the surface of the specimens as possible so that only the normal spectral emissivity was measured. Two thermocouples were symmetrically welded near the measuring area for accurate measuring and monitoring of the temperature at the surface of the specimen. The specimens were heated for 6h at a certain temperature. During this period, the normal spectral emissivity values were measured once every 1min during the initial 180min, and once every 2min thereafter. The measurements were made at certain temperatures from 800 to 1100K in intervals of 20K. One strong oscillation in the normal spectral emissivity was observed at each temperature. The oscillations were formed by the interference between the radiation stemming from the oxidization and nitridation layer on the specimen surface and radiation from the substrate. The uncertainty in the normal spectral emissivity caused only by the surface oxidization and nitridation was found to be approximately 9.5–22.8%, and the corresponding uncertainty in the temperature generated only by the surface oxidization and nitridation was approximately 6.9–15.5K. The model can reproduce well the normal spectral emissivity, including the strong oscillation that occurred during the initial heating period.