Laser surface engineering of Inconel 600 tiles to manufacture high thermal emitters

Inconel 600 is a nickel-chromium based super alloy used in the construction of the vacuum vessel of the Joint European Torus (JET) experimental fusion device. It was selected for its mechanical properties at elevated temperature, being exposed to vacuum baking at >300°C and heat loads of typically 0.5 MW/m² for recessed areas of the JET first wall [1]. In a 2011 JET upgrade, Inconel was also used as a structural & substrate material in the construction of a new wall built to validate the use of metallic plasma-facing components [2]. This paper investigated a new manufacturing route based on nanosecond laser-processing to enhance the surface emissivity of Inconel 600 tiles to use as in-vessel calorimetry targets as part of the JET diagnostics system. Near perfect emissivity from Inconel 600 surfaces was achieved in the measured mid-wave infrared of ~3.2 – 4.7µm by tuning the laser surface processing parameters (fluence, repetition frequency, and feed speed). It was proven that the achieved increase in emissivity was caused primarily by microscale surface structures and that a variable extent oxide layer, when present, could contribute to enhance the emissivity further. This paper presents for the first time a threefold increase of emissivity in Inconel 600 materials achieved via nanosecond laser processing in air. The functionalisation of Inconel 600 hereby presented could be useful for various industrial applications such as passive radiative cooling and thermal management of spacecraft.