Effect of Powder Preparation on the Microstructure and Wear of Plasma-Sprayed NiAl/CrB2 Composite Coatings

The properties of plasma-sprayed composite coatings depend to a large extent on the homogenization of the powders used for their deposition. In order to investigate this relation, mixtures of NiAl and CrB2 (15 and 30 wt.%) powders were prepared via an organic binder (a), hot pressing (b) or sintering (c). The obtained composite agglomerates were sprayed on cylindrical AISI 310S steel pins. Their wear resistance was assessed through a pin-on-disc dry-sliding wear test carried out at 500 °C (a counter-body of NiAl coating was also deposited on AISI 310S). All the composite coatings presented strongly reduced the wear rate when compared with the reference NiAl coatings (9.8 × 10−5 mm3/Nm). Those with 30 wt.% CrB2 addition and obtained via the (a), (b) and (c) routes had 3.8, 2.9 and 1.4 mm3/Nm 10−5, while those with 15 wt.% CrB2 for the same routes had 2.6, 0.9 and 0.7 mm3/Nm 10−5, respectively. The least damage was present in the NiAl (15 wt.% CrB2) coating obtained using route (c), due to the microstructure refinement already achieved at the sintering stage and the good reactive binding of CrB2 with the coating matrix, established during plasma spraying. Increasing the CrB2 addition up to 30 wt.% promotes crack propagation accelerating wear.