Improvement of wear resistance of austenitic steel by combined treatment using electron beam cladding and subsequent plasma nitrocarburizing
The high passivation capacity of austenitic stainless steels leads to excellent corrosion resistance in a wide variety of corrosion media. However, the tribological properties of these steels prove unsatisfactory due to their low hardness and high tendency to adhesive wear. To improve the wear behaviour of austenitic steels while maintaining corrosion resistance, thermochemical processes such as nitriding or nitrocarburizing in plasma can be used. These can be carried out as single process or in combination with coating processes, e.g. hard material coating. Furthermore, high-energy beam technology such as electron beam cladding can be used to generate wear resistant coatings of Fe- or Co-based alloys on austenitic steels.
The present paper presents the results of a new combination treatment consisting of electron beam cladding (EBC) of Co-based alloy (Stellite® 12) and a subsequent plasma nitrocarburizing (PNC). The influence of two different beam deflection techniques on the structure and phase formation of the wear protection layer, the resulting hardness, as well as the bonding of this layer to the base material and the dilution ratio are shown. The subsequent plasma nitrocaburization led to the formation of a 3-4 µm thick layer enriched with nitrogen and carbon.
The characterization of this modified layer was performed using high-resolution imaging techniques (SEM) as well as glow discharge optical emmision spectroscopy (GDOES), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).
The significant improvement in wear resistance compared to the untreated base material was demonstrated by means of abrasive (scratch test) and adhesive-abrasive (pin-on-disc) wear tests. Corrosion resistance was investigated by recording current density potential curves and long-term investigations in corrosive media.