Abstract:
A series of experiments were performed to evaluate some properties of borided 99.5% purity nickel. Boronizing was carried out in a solid media consisting of Ekabor powders at 950 degrees C for 2, 4, and 8 h, respectively Data on intermetallic silicides and borides (Ni5Si2, Ni2B) that formed on the surface of nickel substrate during boronizing were confirmed by st classical metallographic technique and X-ray diffraction (XRD) analysis. It was observed that the predominant phase in the coating layer was a silicide. It is probable that the formation of the nickel silicide laver was due to silicon in the boronizing powder. The hardness of silicides was measured by using a Vickers indenter with a load of 0.5 N. The microhardness of silicides formed on the surface of the nickel substrate reached up to 805 HV. Metallographic studies revealed that the silicide layer has an equiaxed granular morphology, whereas the boride laver formed had a needle-shaped structure. Depending on process temperature and boronizing time the thickness of coating layers ranged from lu to 281 mu m. The thickness of silicide and boride layers depended strongly on the processing time at 950 degrees C. The longer boronizing time resulted in the thicker surface layer. The distribution of alloying elements from the surface to the interior was determined using energy dispersive X-ray spectroscopy (EDS). (C) 2000 Published by Elsevier Science S.A. All rights reserved.
