Plasma processing in carbon containing atmosphere for possible treatment of wind turbine components

Abstract

We propose a new pulse plasma surface treatment consisting of plasma nitriding and subsequent plasma post-nitrocarburizing, which improves the fatigue resistance, wear resistance and corrosion resistance and contributes to the lowering of weighted acoustic level. This process is a candidate for surface treatment of wind turbine gears which are exposed to severe working conditions including high mechanical stresses, alternative load, surface wear and corrosion. During operation, turbine gears can be a source of high sound level which influences the environment. Samples made of steel grades AISI C 1045, 4140 and H11 were pulse plasma nitrided and plasma post-nitrocarburized. The Vickers's method was used for surface microhardness and depth profiling measurements, while the surface zone morphology was examined by the SEM. The surface zone phase analysis was performed by the XRD method while the ball-grinding technique was used to measure the compound zone thickness. A low friction, chemically stable single-phase magnetite superficial layer can be formed by plasma post-oxidation. The post-treatment in a carbon containing atmosphere resulted in the formation of a surface layer with gradually increased carbon content and the formation of the cementite phase, as was found by XRD analyses. A two step plasma process provides the treatment of complex shape workpieces to obtain a nitrided layer with a cementite rich zone at the surface. This was found to be suitable as a candidate technique for wind turbine gears processing.