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.

Powder type and composition have a very important role in the production of metallic and metallicceramic coatings by using the low-pressure cold spray process. Furthermore, structure and mechanical properties of Cu and Cu + Al 2 O 3 coatings are strongly influenced by powder characteristics of Cu particles. The aim of this study was to evaluate the effect of different particle types of Cu powder and different compositions of added Al 2 O 3 particles on the microstructure, fracture behavior, denseness, and mechanical properties, i.e., hardness and bond strength. Spherical and dendritic Cu particles were tested together with 0, 10, 30, and 50 vol.% Al 2 O 3 additions. Coating denseness and particle deformation level increased with the hard particle addition. Furthermore, hardness and bond strength increased with increasing Al 2 O 3 fractions. In the comparison between different powder types, spherical Cu particles led to the denser and less oxide-contenting coating structure due to the highly deformed particles.

Surface engineering can be used to prevent ice accumulation and adhesion in environments that deal with icing problems. One recent engineering approach, slippery liquid infused porous surfaces (SLIPS), comprises a smooth and slippery lubricating surface, where lubricant is trapped within the pores of a solid material to repel various substances, such as water and ice. However, it remains unclear whether the slippery surfaces retain their icephobic characteristics under the impact of supercooled water droplets or repeated freezing and melting cycles. Here, the icephobic properties of SLIPS are evaluated under multiple droplet freeze–thaw and ice accretion–detachment cycles and compared to hydrophobic and superhydrophobic surfaces. The experiments are designed to mimic real environmental conditions, thus, the icephobicity is investigated in icing wind tunnel, where ice accretion occurs through the impact of supercooled water droplets. The adhesion of ice remained extremely low, <10 kPa, which is four times lower than ice adhesion onto smooth fluoropolymer surfaces, even after repeated ice accretion–detachment cycles. Moreover, cyclic droplet freeze–thaw experiments provide insight into the effects of temperature cycling on SLIPS wettability, showing stable wetting performance. The results suggest liquid infused porous surfaces as a potential solution to icephobicity under challenging and variating environmental conditions.

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.