"Processamento, Caracterização Mecânica e Tribológica do Compósito Al2O3-NbC."

Abstract

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Influence of NbC Content on the Wear Resistance of Alumina/Niobium Carbide Tools

“…In the literature, there is a wide range of reported hardness data for composites owing to differences in the processing routes, responsible for distinct microstructures. Our results are close to the earlier reported values for Al 2 O 3 -NbC composites, ranging from 15.6 GPa to 26.0 GPa, depending on the processing route and indentation load 9,[18][19][20] .…”

“…Table 2 presents the hardness results for selected samples. Assuming pure Al 2 O 3 and NbC have Vickers hardness of 17.3 and 19.6 GPa 10,18 , respectively, the hardness of the composites is predicted to range from 17.4 (5 wt% NbC) to 17,7 (30 wt% NbC) GPa, based on the volumetric mixture rule. The measured hardness clearly increased as a function of the NbC content, but much more proportional than predicted.…”

“…The measured hardness clearly increased as a function of the NbC content, but much more proportional than predicted. The increase in the hardness with the addition of a second phase can be explained by the restriction of the plastic deformation of the matrix phase in the neighborhood of the reinforcement particles, changing the crack propagation mechanisms and the type of fracture and also by decreasing the grain size of the matrix 6,18 . As shown in recent studies, a larger amount of NbC provides smaller Al 2 O 3 grain sizes, increasing the hardness 9 .…”

“…These films can be either alumina hydroxide formed during wear by the reaction of alumina with humidity or material transfer from the pin during the wear process. Ferreira, in his studies of Al 2 O 3 -NbC composites 18 , performed wear tests at different relative humidity levels (from 26% to 76%) and observed that the formation of the films was much more noticeable at higher humidity levels. Tough the tests were carried up at room temperature and a relative humidity of 50%, the formation of a lubricating Nb 2 O 5 tribofilm caused by the oxidation of NbC is also expected, as reported by Woydt and Mohrbacher 4 .…”

“…Figure 7 presents the wear rates for the different composites, compared to that reported for pin-on-disk tests against Al 2 O 3 spheres of Al 2 O 3 -NbC composites with 20 wt% 19 and 5 wt% of NbC 18 . The wear rate linearly decreased with the NbC content.…”