Cr 2 O 3 coatings and Cr 2 O 3 -based binary coatings offer high hardness, excellent sliding wear performance and corrosion resistance. Therefore, they are widely applied in the paper and textile industry, as well as for pumps and mechanical sealing systems. Compared to the conventional spray processes, the technology of Suspension-HVOF (high velocity oxy-fuel flame spraying of suspensions, S-HVOF) using submicron-scaled raw materials allows the production of dense, finely-structured coatings with smooth surfaces and improved mechanical properties. This work investigates the microstructure and performance of Cr 2 O 3 and Cr 2 O 3 -15wt.%TiO 2 coatings obtained by SHVOF with water-based suspensions. For the development of the binary composition two routes were used to produce ready-to-spray suspensions: i) dispersion of an appropriate alloyed material in the solvent and ii) mixture of two stable suspensions in the desired ratio. In order to evaluate the potential of suspension spraying over the conventional APS and HVOF processes, the mechanical properties and the corrosion resistance of the S-HVOF Cr 2 O 3 and 85Cr 2 O 3 /15TiO 2 coatings were compared with the coatings produced from spray powders. From the experimental results it was observed that the suspension sprayed coatings showed in most of cases denser microstructure, good mechanical properties and superior corrosion performances.

Thermal spray coatings produced from suspensions can be precisely tuned in terms of thickness, surface morphology, microstructure, and properties. This paper discusses the benefits of using suspensions as feedstocks for atmospheric plasma and HVOF spraying, the equipment required, and the technological challenges that remain to be solved.

In this work suspension-HVOF spraying (S-HVOF) was used to prepare dense and mechanical stable Al 2 O 3 sprayed coatings with high contents of α-Al 2 O 3 phase. Aqueous suspensions with various contents of powder (from 25 wt.% up to 50 wt.%) have been developed starting from two commercial α-Al 2 O 3 powders, characterized by different purity and particle sizes. The suspensions have been internally injected in a modified combustion chamber of a HVOF TopGun-torch. Coating microstructures, phase compositions and mechanical properties resulting from the interaction between suspension characteristics and spray parameters are presented. Use of suspensions with high solid contents allowed the production of thick, dense and mechanically stable coatings. The α-Al 2 O 3 was the main phase in the coatings produced through the injection of suspensions containing powders with very high purity.

In this paper the characteristics (microstructure, phase compositions) and electrical insulating properties of thermally sprayed alumina coatings produced by suspension-HVOF (S-HVOF) process and conventional HVOF spray method are compared. The electrical resistance (electrical resistivity) and dielectric strength were investigated using DC-electrical resistance measurements, electrochemical impedance spectroscopy (EIS) and dielectric breakdown test. The electrical resistance was determined at room temperature at different relative air humidity (RH) levels, from 6% RH up to 97% RH. Differences in the electrical insulating properties due to the different coating characteristics are discussed. The suspension-sprayed Al 2 O 3 coatings showed better electrical resistance stability at high humidity levels (> 75% RH), which could be explained by a specific microstructure and retention of a higher content of α-Al 2 O 3 . Nonetheless, the values of dielectric breakdown voltage and dielectric strength recorded for suspension sprayed coatings were lower than those of HVOF coatings.

This paper describes the properties and behaviors of alumina and titania coatings that have recently been produced using suspension spraying techniques. It examines coating microstructures and phase compositions are shows how they are influenced by different operating parameters and interactions. A selection of new experimental results obtained by the authors is also presented. In the case of Al 2 O 3 , the goal was to retain a high ratio of the thermodynamically stable α-phase. In the case of TiO 2 , the spraying process was optimized to preserve the anatase phase in order to obtain photocatalytically active layers.

Functional characteristics of materials including the mechanical, electrical, environmental and tribological performance can be significantly improved using nanostructured feedstock. Over the last few years much research has been dedicated to the development of thermal spraying techniques with liquid precursors to prepare fine nanostructured coatings. In this work nanostructured ceramic coatings were prepared using the technique of suspension spraying. Titania and alumina powders with sizes in the nanometre to submicrometre range were used to prepare aqueous and alcoholic suspensions. Atmospheric plasma and high-velocity flame were employed as enthalpy sources. The morphologies and crystalline structures of the sprayed ceramics were mainly characterised by SEM and XRD. The aim of this work was to carry out a comparative study and to discuss the nanostructured ceramic coating microstructures as a function of the physicochemical properties of the feedstock suspensions and spraying parameters.