Tribological evaluation of Fe-B-TiB2 metal matrix composites

Iron and titanium borides have been widely used for the production of metal matrix composites (MMC). The majority of the studies focus on the Fe-TiB2 and/or the Fe-TiB2-TiFe2 region of the ternary Fe-Ti-B diagram, whereas the Fe-TiB2-Fe2B area has not yet been systematically studied, although it combines two very hard particles, namely TiB2 and Fe2B. This research deals with the wear behavior and tribological evaluation of Fe2B-TiB2 MMC layers, which were successfully produced on the surface of plain carbon steel, using the plasma transferred arc (PTA) technique. The counterbody, either tool steel or alumina ball, plays an important role in the wear rate and friction coefficient of the boronized surfaces. The “free” boron content in the Fe-TiB2-B system, i.e. boron not bound in TiB2, affects the tribological behavior of the alloyed layers. With steel as the counter-body material, “free” boron content increases the wear rate due to the formation of a more brittle matrix which is easily removed by adhesion, while with the alumina counter-body it has the tendency to decrease the wear rate, as the strengthened matrix can resist better to abrasion. The friction coefficient values for the tool steel ball are smaller than those of the alumina ball, owing to the different wear mechanisms involved.