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This paper aims to evaluate the dry sliding wear of AISI 304 austenitic stainless steel as a function of the applied load. Samples of AISI 304 were heat treated (sensitized) to precipitate Cr23C6 carbides in the grain boundaries, and the resulting microstructure was compared to that of the non-sensitized samples. Wear testing was carried out at room temperature of 25°C and a relative humidity of about 60% using a pin-on-disk apparatus. The load applied was varied from 10 to 30 N at a constant sliding velocity of 0.5 m s–1. Wear particles were analyzed by means of scanning electron microscopy and X-ray diffraction. The results showed that the dynamic friction coefficient remained effectively constant with increasing applied load. The surface hardness measured after the wear process generally increased at higher loads due to subsurface strain-hardening, and deformation-induced martensitic transformation occurred during the wear process. Surface roughness and weight losses were found to increase with increasing the load for both sensitized and non-sensitized samples. In addition, a great amount of Cr23C6 carbides in the grain boundaries favored a size reduction of the debris generated due to wear.

Metal matrix composites (MMCs) are relatively new materials on science and materials engineering. In this work was used single-walled carbon nanotube (SWNT) as reinforcement in an aluminum matrix. For this purpose, 0.75% (by weight) of SWNT was dispersed with isopropanol using ultrasonication and mixed with particles of aluminum powder. The samples with and without SWNT were dried and compacted at room temperature with a pressure of 400 MPa for obtain a billet with 4,8x4,8x25,0 mm3. These compacted billet were subjected to Equal-Channel Angular Extrusion - ECAE (Φ=90 °) at room temperature. The influence of the presence of SWNT, of the number of extrusion passes (0, 1, and 3 passes), of the extrusion route (A or BC) and of the use of back pressure (0-65 MPa) in densification and hardness of the composite was evaluated. Optical microscopy was used to characterize the morphology of the aluminum grains, the dispersion of SWCNT and present pores in the samples. The results indicated that the density and hardness of the samples are increased with the increase in the number of extrusion passes and the use of back pressure. The microstructures showed alignment of the aluminum grains and of the CNT clusters in a direction close to the shear imposed by the ECAE process and increase of the dispersion because of the necking and defragmentation of the CNT clusters.

This study aims to evaluate the behavior of thermally sprayed coatings with the HVOF technique (High Velocity Oxygen Fuel), subject to tribological testing of reciprocal movement with the SAE 52100 flat steel pin, in accordance with ASTM G 133. The carbon with Cr2C3-25NiCr and WC-12Co were evaluated under conditions of intense surface fatigue. The microstructure and surface modifications were analyzed by optical microscopy and scanning electron microscopy. By using these techniques were possible to compare the modifications of the coatings under repeated loading conditions, and to expand the knowledge about wear mechanisms, mainly the adhesive one, present in several mechanical components, particularly in bearing and internal combustion engines. The coatings tested showed lower wear rate when compared to SAE52100 steel and equivalent behavior among the different loading conditions applied.