Wear behavior of Fe3Al-TiN-TiB2 HVOF coatings: A comparative study between in situ and ex situ powder processing routes

In the present study, the tribological properties of High Velocity Oxy-Fuel (HVOF) coatings prepared from Fe3Al-based composite powders were investigated. The iron aluminide matrix of the composite powders was reinforced with TiN and TiB2 particles made using two different processing routes: a) an in situ method where fine ceramic particles were formed in the matrix by the reaction between Ti and BN, and b) an ex situ method where preformed coarse TiN and TiB2 particles were added to the matrix. The tribomechanical performance of the coatings was assessed using indentations and pin-on-disc wear tests. Compared to ex situ samples, the Fe3Al-based coatings strengthened with in situ ceramic particles exhibit higher microhardness and wear resistance regardless of the sliding velocity. The presence of voids, cracks and scratches/grooves in the wear track of the in situ coatings and the coating material transferred to the corresponding counterpart suggest that coatings with fine reinforcing particles fail predominantly via delamination and adhesive wear mechanisms. In the case of the ex situ coatings, the presence of a significant amount of hard ceramic particles within the wear track indicates that abrasive wear plays a dominant role in the degradation mechanism. Oxidation wear also contributed to material removal at high sliding velocity since transfer materials inside the wear track contain a high oxygen content compared to the unworn region regardless of the coating type.