Infrared thermography of thermal spray coating processes as quality monitoring tool

The evolution of substrate surface temperature during coating deposition is a decisive property-determining factor in thermal spraying. Local heat development is influenced by various factors such as thermal conductivity and substrate thickness. High fluctuations in surface temperatures promote the formation of residual stresses in the coating layers during cooling. Therefore, the risk of oxidation, cracking, or delamination increases. Therefore, limiting the surface temperature appears beneficial for quality assurance. Infrared (IR) thermography offers the possibility to determine the surface temperature in the coating process without contact. Determining factors in temperature evolution during the thermal spray process were identified by using IR thermography. The interaction between the substrate and coating material was taken into account. Furthermore, application limits for IR thermography (Optris XI80) in comparison to thermocouple measurements for the temperature range of 0–250 °C were determined. For this purpose, the stainless steel AISI 316L was coated on aluminum and steel sheets by atmospheric plasma spraying (APS). The influence of substrate thickness was evaluated. A correlation between the temperature history during the coating process and the corrosion properties was established. Current density potential measurements using gel electrolytes were used for this purpose. Clear correlations between the development of the surface temperature and the resulting coating properties werederived.