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

Abstract

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 CrB 2 (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-ondisc dry-sliding wear test carried out at 500°C (a counterbody 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 9 10 -5 mm 3 /Nm). Those with 30 wt.% CrB 2 addition and obtained via the (a), (b) and (c) routes had 3.8, 2.9 and 1.4 mm 3 /Nm 10 -5 , while those with 15 wt.% CrB 2 for the same routes had 2.6, 0.9 and 0.7 mm 3 /Nm 10 -5 , respectively. The least damage was present in the NiAl (15 wt.% CrB 2 ) coating obtained using route (c), due to the microstructure refinement already achieved at the sintering stage and the good reactive binding of CrB 2 with the coating matrix, established during plasma spraying. Increasing the CrB 2 addition up to 30 wt.% promotes crack propagation accelerating wear.

Effect of Heating on the Microstructure of NiAl + CrB2 Coatings Deposited by Mechanical Embedding in a Ball Mill

“…This results in the formation of medium-thickness coatings with very rough surfaces as described elsewhere (Szlezynger et al, 2018). The high-energy milling of nickel and aluminum elemental powders at the ratio of 50:50 at% (Chen et al, 1999; Joardar et al, 2007) or prealloyed NiAl intermetallic powders (Poliarus et al, 2019) usually produces powder consisting of rounded agglomerates of nanocrystallites. Their consolidation with eliminated porosity was achieved with high-temperature hydrostatic extrusion (Awotunde et al, 2019) or shock-consolidation (Chen et al, 1999).…”

“…Among the MMC coatings, PS deposited NiAl+15 wt% CrB 2 ones have turned out to be especially effective in this role, as their presence has helped to decrease the wear rate at 500°C by five times (Poliarus et al, 2019). They are characterized by good adhesion and a relatively uniform distribution of the strengthening phase.…”