Three body abrasion wear of low carbon steel modified surfaces

The wear performance of four different coatings applied on a low carbon steel substrate by the plasma transferred arc (PTA) technique is investigated under low stress abrasion conditions, using the dry sand/rubber wheel apparatus (DSRW test). The coatings belong to two major categories: two of them are tool steels with very hard particles (respectively, TiC and M2C/M6C carbides) in their matrix, the other two are boride coatings (belonging to the Fe–B and Fe–Cr–B systems, respectively) and consisting of large proeutectic borides in a eutectic matrix. It is shown that the wear rate of all coatings increases linearly with the applied load, according to the Archard law. However, above a certain load the wear rate of the coating belonging with the Fe–B system catastrophically increases, mainly due to its brittleness associated to the presence of FeB type borides. The wear rate of the other three coatings diminishes above a critical load, because the silica sand abradant suffers from blunting, under the action of high pressures against the very hard particles of the coatings. The wear mechanisms revealed through extensive metallographic investigation show that although the hardness is a very crucial parameter, other factors, like the brittleness of the material, the microstructure and eventually phase transformations induced during the wear test may change the wear behaviour of the coatings, reversing the ranking anticipated if one was based on their hardness.