This paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC-10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes.

This paper provides a comprehensive characterisation of HVOF-and HVAF-sprayed Cr 3 C 2-25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr 3 C 2 than the feedstock powder, possibly due to the rebound of some Cr 3 C 2rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter-and intra-lamellar cohesion, being higher (Z 70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (E5x10 À 6 mm 3 /(Nm)). At 400°C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from E0.7 to E 0.5. The thermal expansion coefficient of the coatings (11.08x10 À 6°C À 1 in the 30-400°C range) is sufficiently close to that of the steel substrate (14.23x 10 À 6°C À 1) to avoid macro-cracking.

Thermally-sprayed alumina based materials, e.g., alumina-titania (Al 2 O 3 -TiO 2 ), are commonly applied as wear resistant coatings in industrial applications. Properties of the coatings depend on the spray process, powder morphology, and chemical composition of the powder. In this study, wear resistant coatings from Al 2 O 3 and Al 2 O 3 -13TiO 2 powders were sprayed with plasma and high-velocity oxygen-fuel (HVOF) spray processes. Both, fused and crushed, and agglomerated and sintered Al 2 O 3 -13TiO 2 powders were studied and compared to pure Al 2 O 3 . The coatings were tested for abrasion, erosion, and cavitation resistances in order to study the effect of the coating structure on the wear behavior. Improved coating properties were achieved when agglomerated and sintered nanostructured Al 2 O 3 -13TiO 2 powder was used in plasma spraying. Coatings with the highest wear resistance in all tests were produced by HVOF spraying from fused and crushed powders.

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