Effect of substrate temperature control during deposition on the adherence of ion-plated titanium carbide and vanadium carbide films on molybdenum

Molybdenum has been proposed as a material for protective or liner plates of fusion reactor first wall components. To avoid the introduction of high Z impurities such as molybdenum into the plasma, low Z coatings for the molybdenum are required. We investigated controlled heating of the substrate during deposition in an attempt to obtain strong adhesion across a film-substrate boundary. Using acetylene gas as the carbon source titanium carbide was ion plated onto the molybdenum substrate, whose temperature was increased at a rate of 40-80°C min^-1 and finally maintained at 800°C or more until the end of the coating process. Coatings about 25 μm in thickness obtained by this method were thermally cycled 100 times with an IR image furnace between 200-1200°C at a heating rate of 100°C s^-1; no evidence of adhesion failure was obtained. Vanadium carbide coatings also showed good resistance against film exfoliation, although microcracks were observed after the thermal cycle test.