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Thermal spraying allows the production of overlay protective coatings of a great variety of materials, almost without limitations as to its components, phases and constituents on a range of substrates. Wear and corrosion resistant coatings account for significant utilization of thermal spray processes. Besides being a means to evaluate the coating tribological performance, erosion testing allows also an assessment of the coating toughness and adhesion. Nevertheless, the relationship between the erosion behavior of thermal sprayed coatings and its microstructural features is not satisfactorily understood yet. This paper examines room temperature solid particle erosion of zirconia and alumina-based ceramic coatings, with different levels of porosity and varying microstrucutre and mechanical properties. The erosion tests were carried out by a stream of alumina particles with an average size of 50 µm at 70 m/s, carried by an air jet with impingement angle 90°. The results indicate that current erosion models based on hardness alone cannot account for experimental results, and, that there is a strong relationship between the erosion rate and the porosity

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ResumoO mexilhão dourado ou Limnoperna fortunei é um organismo invasor que tem causado grandes prejuízos a sistemas de captação de água e usinas hidroelétricas, sendo que, mais recentemente, vem causando danos ao deslocamento de embarcações fluviais em águas do Pantanal Mato-Grossense. No presente trabalho, foi feito um estudo, em laboratório e em campo, de materiais antiincrustantes. A relação entre a força de desligamento do mexilhão dourado e a energia livre de superfície foi avaliada. Foram selecionados materiais com baixa energia de superfície como polímeros e alta energia de superfície como materiais metálicos. Qualitativamente, o desempenho do aço inoxidável e o desempenho do cobre, testados em laboratório e em campo, se apresentaram, relativamente, consistentes entre si e com dados da literatura. E, com os dados obtidos, percebe-se que há relação entre energia livre de superfície e o caráter antiicrustante do Limnoperna fortunei, mas, até o momento, não se pode afirmar que se trate de uma correlação linear, pois pode ser que outros fatores dos materiais estejam influenciando no comportamento dos organismos. Os dados sugerem, ainda, que a componente ligação de hidrogênio apresenta o principal efeito em termos de energia livre de superfície. Palavras-chave:

Ni-P chemical coatings have been used to prevent wear, corrosion and as an alternative for hard chromium, since the latter's deposition processing is very harmful to the human health and the environment. In the present paper, Ni-P coatings with 8 and 10% P were deposited in steel AISI 1020 and thermally treated. Ni-1wt%P coatings with incorporation of hard particles of Al2O3 were also investigated. The microstructure and phase relationships were analyzed and correlated with the fracture toughness and scratch hardness of the coatings.The results show that the fracture toughness of the coating was smaller when thermally treated at 400°C for 1 hour and the scratch hardness reached a peak in this temperature. The relation of chemical composition and microstructure with mechanical properties of Ni-P coatings is presented. The phosphorus contents, the crystallization, and the incorporation of hard particles in the coatings change the values of toughness fracture and scratch hardness.

The effects of combustion thermal spraying parameters namely combustion pressure, feeding rate, and carrier gas on the wear resistance, friction coefficient, and Knoop hardness of poly (ethylene terephthalate) (PET) films were investigated. The PET coatings were characterized by measuring the wear coefficients by calowear-type testing, the friction coefficients by a pin-on-disk test, and Knoop hardness. The abrasive wear and friction coefficients of the coatings were compared with the values of a post consumer PET bottle chip reference sample. The structural characteristics of the coatings were investigated by X ray diffraction. Statistical analysis of the results allowed for the systematic characterization of the influence of the process variables mentioned above on the coating wear, friction, and microhardness values. Specifically, this study shows that the process parameters affect the wear coefficient and Knoop hardness significantly, but not the friction coefficient. The degree of crystallinity of the PET coatings varied from 20 to 26%. Keywords: thermal spray, PET, tribology*e-mail: rogerioxavier@yahoo.com.br, jose.branco@cetec.br, vilmaccosta@hotmail.com, calado@eq.ufrj.br 122 Nunes et al. Materials Researchparameters were 10 rpm, 14 mm trail diameter, 10-N load, 50 turns, and a traveled distance of 2,200 mm. Each sample was measured in triplicate. The samples were weighed before and after testing for calculation of mass loss. Wear testAbrasive wear was evaluated by calowear testing, which involves the interaction of a rotating steel sphere with the sample surface with alumina as an abrasive. A semi-spherical crater was formed on the contact surface of the sample. The wear rate was calculated from the crater dimension using Equations 2, 3, and 4:where D is the crater diameter, n the number of turns, R the sphere radius, V the lost volume, S the sliding distance, and Q the wear rate 12 .The wear coefficient (K) was calculated with the Archad equation 10 , where W is the applied load and H the hardness.The sliding distances of the sphere were 100, 200, 300, 500, and 1000 turns and the applied load was 13.7 N. Each sample was measured in triplicate. The crater diameter was measured by 3D profilometry. Results and Discussion Coating structureUsing an optical microscope, the presence of bubbles or pores at the substrate/coating interface and in the PET coating medium was not observed. However, they were observed on the coating-free surface. The formation of bubbles is explained in the following way. The final coating temperature was around 410 °C, below the degradation temperature of PET (420 °C). Apparently, the temperature reached by the deposited layers was sufficient for their complete coalescence between the substrate and the coating medium. Particle degradation was insignificant. This will be further discussed with the results of the infrared spectroscopy. Due to the heterogeneous size of the PET particles, the smallest ones probably melted, while the larger ones were semi-melted. During the natural cool...