Efficiency and behavior of textured high emissivity metallic coatings at high temperature

• Texturing metallic surfaces increases the total emissivity.
• Emissivity at high temperature was measured on textured metallic surfaces.
• A total hemispherical emissivity of 0.8 was obtained for a Re coating on TZM alloy.
• Comparison of emissivity data is given for the three materials studied.
• The highest emissivity was obtained on the finest surface texture.

Three metallic coatings with textured surfaces, made of rhenium, tungsten and molybdenum, were studied in the frame of the Solar Probe Plus mission (NASA) as candidate materials. The role of these coatings is to dissipate a maximum of energy from a hot instrument facing the Sun, by the mean of their high total hemispherical emissivity. The total hemispherical emissivity of the three coatings was measured in the temperature range 1100–1900 K, as well as over time in order to study their high temperature stability. Various emissivity levels were obtained depending on the surface texture. The highest total hemispherical emissivity was obtained on a rhenium coating, with an emissivity of 0.8 in the temperature range 1300–1700 K. However, this rhenium coating with a fine, sharp surface texture, presented an instability at high temperature, which might limit its optimal operating temperature to about 1500 K. As for the tungsten coating, the total hemispherical emissivity was increased by a factor 2 due to the enhanced surface texturation and its great stability over the whole temperature range was shown.

Various high emissivity levels were obtained with metallic coatings with different surface patterns at the micron scale.Figure optionsDownload as PowerPoint slide