BORIDING OF FERROUS AND NON-FERROUS METALS AND ALLOYS IN FLUIDISED BED REACTOR

摘要

Heat treatment of alloys in fluidised bed reactors has been carried out for more than twenty five years. Recently this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers. In the present study fluidised bed technology (FBT) has been used to deposit boride coatings on ferrous and non-ferrous metals and alloys. The coatings were examined by means of optical microscopy, X-ray diffraction, and Vickers microhardness testing. These techniques were used to characterise coating thickness and morphology, phase formation, and hardness. The as produced coatings were generally characterised by very good adherence and uniformity. On 0.5 wt- percent C steel it was found that only one phase, Fe_2B, was formed during the treatment. Fluidised bed bonding of various steel substrates produced boride layers similar to those obtained by the pack cementation bonding method. On pure Ti, a TiB layer was found, while on Ti-6Al-4V alloy both TiB and TiB_2 phases were detected. Bonding pure Ni gave mainly a Ni_3B coating, while bonding pure Co produced both Co_4B and Co_3B layers. The bonded Ni showed improved tribological properties under dry wear conditions.