Abstract: The process for making a structural element subjected to a high thermal stress and made of a material of high thermal conductivity such as molybdenum, tungsten, copper, aluminum or an alloy of these metals with a protective layer protecting the surface of the structural element comprises treating the surface of the structural element to remove surface impurities present and then coating the surface with an amorphous hydrogen containing carbon layer. For reduction, i.e. removal, of the surface impurities the structural element can advantageously be exposed to a hydrogen flow containing hydrogen atoms and/or ions at a temperature of from 100.degree. C. to 600.degree. C. at a pressure of from 10.sup.-2 to 10.sup.2 Pa. The hydrogen atoms and/or the hydrogen ions coming in contact with the surface of the structural element are formed by contact dissociation at at least one hot surface or by glow discharge or by electron cyclotron resonance and the volatile products are pumped away.