Micro-abrasive wear mechanisms of P/M AISI M2 steel with different surface treatments

Boriding, heat treatment (quenching and tempering) and PVD (Physical Vapor Deposition) film deposition were applied to P/M (Powder Metallurgy) AISI M2 steel. Four sample conditions were produced: Quenched and tempered AISI M2 (QT), Borided AISI M2 (B), Quenched and tempered AISI M2 + Film (QTF) and Borided AISI M2 + Film (BF). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Vickers microhardness test. The load applied in the micro-abrasion tests (fixed-ball) was 0.49 N and abrasive slurry concentration was 0.1 g/cm3. Silicon dioxide (SiO2) abrasive powders (approximately 80% of particles between 1 and 5 μm) were used in the abrasion experiments. Wear coefficient and mechanisms of all conditions were compared. The XRD analysis revealed the presence of a biphasic layer of borides (FeB and Fe2B phases) on the borided samples. The film thickness was 2.1 ± 0.4 μm and the hardness of the multilayered AlTiN/CrN film was about 3912 HV0.025. The borided layer thickness was 46.5 ± 5.1 μm and the hardness average of 2162 HV0.025. The wear mechanism for the QT and QTF samples was two-body abrasion (grooving abrasion). There was a reduction on the signs of grooving abrasion for the B and BF samples due to the increase in plastic deformation resistance.