Thermal imaging systems, namely dual-wavelength pyrometers, have drawn attention to study DED processes because they utilize the ratio of the relative intensities of radiation at two different wavelengths. An advantage of this method is that it is independent of the absolute emissivity value, thus providing a more accurate temperature measurement, with a reported error range of ±6°C.

The thermal behavior of 316L stainless steel was investigated with an imaging pyrometer in the dynamic range of 1500 ~ 2500K. The thermal gradient and cooling rate of the melt pool and surrounding area are derived from temperature profiles, which show that the temperature gradient in the center of the pool is ∼103 K/mm, and the cooling rate for this 102 d treatment area is ∼104 K/s. One limitation of the thermal imaging method is that the entire thermal history of the deposited component, especially the temperature change of the cured material, cannot be obtained.