Laser surface alloying of ferritic Fe-40Cr alloy with ruthenium

An investigation is made of the laser surface alloying of an experimental ferritic Fe-40Cr alloy with a ruthenium powder coating using a continuous wave CO₂ laser. The micro structure and corrosion behaviour of the laser surface alloying layer and the Fe-40Cr bulk alloy were examined by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, microhardness, potentiodynamic and corrosion potential measurements. The results of the microstructural examination showed that fine cellular dendrites with a ruthenium content as high as 51.84wt.% were produced by laser surface alloying. The extended solubility of ruthenium in the cellular dendrites resulted in a dramatic increase of the hardness in the laser alloying layer. Potentiodynamic and open circuit corrosion potential measurements indicated that the ruthenium-containing surface layer spontaneously passivated in hydrochloric and sulphuric acid solutions, whereas the bulk Fe-40Cr alloy remained in the active state when exposed in these reducing acid solutions. © 1997 Elsevier Science S.A.