There are several challenges when designing components exposed to harsh environments. Cases such as hydraulic turbines and marine propellers are classic examples of demands for materials capable of withstanding erosion and corrosion wear. To enhance and recover worn surfaces, it is usual the use of coatings. This study proposes a new series of coatings based on diffusional effects observed for thermally sprayed chromium carbide coating. A columnar morphology was observed, due to the diffusional gradient perpendicular to the surface. The coating has also shown an absence of porosity and peculiar properties.

Erosion and abrasion are both wear processes in which a particle that strikes the surface removes material, either by impact (erosion) or contact (abrasion). These wear processes can cause damages to components, which can be protected by coatings to reduce the damage occurrence. Thermally sprayed coatings are considered candidates for a protective system against abrasion and erosion. The HVOF spray process is one of the most used thermal spray processes due to the ability of producing dense coatings, with good values of hardness and toughness. Among the materials used in thermally sprayed coatings, WC-Co based coatings are often used, as it offers a combination of high hardness, toughness and adherence, which can provide a good wear resistance. In this work, the influence of different HVOF process parameters, specifically the type of fuel used, on the residual stresses and properties of these coatings was studied. It was noted that coatings deposited by HVOF with kerosene liquid fuel, presented lower porosity, compared with coatings deposited by gas fuel. It was also observed that the coatings with lower porosity provide a better abrasion resistance, meanwhile the erosion was controlled by toughness for 30° and higher hardness for 60° of impact angle.

Aluminum coatings applied by thermal spraying are widely used for protection against marine corrosion. The HVOF process produces aluminum coatings with high particle velocity, at a higher temperature for longer, permitting a high adhesion among the deposited particles. The objective of this work was to analyze how the microstructure of the aluminum coating sprayed by HVOF was formed on different complex surfaces. The influence of different deposition process parameters on the coating, varying the angle of incidence during deposition, substrate preheating and nitrogen flow was studied. Outer corner and convex surfaces presented greater uniformity in the formed microstructures. The angle of incidence was the most influential parameter on the coatings, filling complex profiles better, with 60° of incidence, although the 90° of incidence increased the adhesion. The potentiodynamic polarization test was performed to evaluate the corrosion resistance of coatings. The higher preheating and lower angle of incidence increased the corrosion resistance of coatings. Corrosion tests in salt spray are in progress in order to compare with continuous results.

The HVOF process is characterized by the deposition of a low porosity and oxide content coating and the particles projected by this process have high kinetic energy, resulting in a high density coating. However, the presence of non-melted particles can affect the porosity, tensile adhesion, hardness and surface finishing. In this article, the influence of the shot peening treatment on morphology, porosity, tensile adhesion and roughness of some FeMnCrSi(Ni/B) HVOF coatings have been studied. High carbon steel particles with spherical geometry were used for shot peening. The results show that the shot peening reduces the porosity, mainly in the coatings with higher porosity level, and generates an increase of hardness with no phase transformations. The increase in adherence is also a benefit generated by the treatment. The surface quality analyses show a significant roughness reduction. With shot peening a compressive residual stress state was achieved in the coating, improving mechanical properties.

Cavitation erosion is a mass loss process that occurs in a component subject to a liquid pressure variation. The mass loss phenomena occurred by extensive microstructure deformation with combination of shock loading and fatigue caused by the impact and collapse of the bubbles at surface. Many studies have been done to evaluate the cavitation resistance of the thermally sprayed coatings. Oxide formation, microstructure and tensile adhesion are important characteristics for coatings against cavitation. In this work some Fe-Mn-Cr-Si alloys, that is a class of steel with strain induced phase transformation, were used to evaluate the chemical composition influence on the microstructure, oxide formation, chemical composition and tensile adhesion of HVOF coatings. It was observed a significant reduction on the porosity, from 3% to 0,1%, and area fraction oxide from 15% to 7%, with Boron and Nickel addition. A combination of Nickel and Boron addition improve the wettability of the splats with increase on the tensile adhesion of the coatings, up to 60MPa, otherwise, higher levels of Boron content reduce the adhesion of the coatings.

Ceramic coatings are applied in mechanical components subject to high temperature conditions, normally are deposited by plasma thermal spraying process. In this work, the porosity of YSZ ceramic coatings, deposited with different parameters conditions were analyzed by optical microscopy, scanning electron microscopy using back-scatter electron (SEM-BSE) detector and ultrasonic technique. It was verified that porosity measurement by optical and scanning electron microscopy is very sensitive with respect to metallographic preparation, mainly cutting process, and gray level adjustment. SEM-BSE technique showed less scatter results with easier porosity visualization, compared with optical microscopy. The porosity of the coatings was also measured by ultrasonic technique. It was observed that the ultrasonic velocity increase with porosity reduction. Ultrasound technique showed a good correlation with OM and SEM porosity measurement.