Adhesion behaviour of borided AISI 4140 steel

In this study, the adhesion behaviour of the borided AISI 4140 steel was estimated. A di-iron boride layer (Fe₂B = ∼22 µm) was obtained on the surface of the AISI 4140 steel preheated at 773 K for 30 min to prevent thermal shock; afterwards, the samples were exposed to 1173 K for 30 min. The scratch tests were developed over the surface of the Fe₂B/substrate system using a Rockwell-C diamond indenter with a normal force increasing from 0.5–80 N. The friction coefficient behaviour and the residual depth values were measured considering the scratch length that was monitored during the test, according to the ASTM C1624 standard procedure. Critical loads were determined through the combination of the normal force and visual inspection over the worn surface with cracks (cohesive failure) or detachment (adhesive failure) and are explained according to the mechanical properties of the Fe₂B/substrate system.