Microhardness and friction coefficient of multi-walled carbon nanotube-yttria-stabilized ZrO2 composites prepared by spark plasma sintering

Multi-walled carbon nanotubes (eight walls) are mixed with an yttria-stabilized ZrO2 powder. The specimens are densified by spark plasma sintering. Compared to ZrO2, there is a 3.8-fold decrease of the friction coefficient against alumina upon the increase in carbon content. Examinations of the friction tracks show that wear is very low when the carbon content is sufficient. Exfoliation of the nanotubes due to shearing stresses and incorporation of the debris into a lubricating film over the contact area is probable

Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic-CNFs composites

Alumina-carbon nanofibres (CNFs) and silicon carbide-CNFs nanocomposites with different volume fraction of CNFs (0-100vol.%) were obtained by spark plasma sintering. The effect of CNFs content on the tribological behaviour in dry sliding conditions on the ceramic-carbon nanocomposites has been investigated using the ball-on-disk technique against alumina balls. The wear rate of ceramic-CNFs nanocomposites decreases with CNFs increasing content. The friction coefficient of the Al 2O 3/CNFs and SiC/CNFs nanocomposites with high CNFs content was found to be significantly lower compared to monolithic Al 2O 3 and SiC due to the effect of CNFs and unexpectedly slightly lower than CNFs material. The main wear mechanism in the nanocomposite was abrasion of the ceramic and carbon components which act in the interface as a sort of lubricating media. The experimental results demonstrate that the addition of CNFs to the ceramic composites significantly reduces friction coefficient and wear rate, resulting in suitable materials for unlubricated tribological applications. © 2011.This work has been carried out with financial support of National Plan Projects MAT2006-01783 and MAT2007-30989-E and the Regional Project FICYT PC07-021. A. Borrell acknowledges the Spanish Ministry of Science and Innovation for her FPI Ph.D. grant. We would like to thank the people from Institute Technological of Materials (ITM) of the Polytechnic University of Valencia for helping us with the tribology experiments during A. Borrell's short stay in 2009.Borrell Tomás, MA.; Torrecillas, R.; Rocha, VG.; Fernandez, A.; Bonache Bezares, V.; Salvador Moya, MD. (2012). Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic-CNFs composites. Wear. 274:94-99. https://doi.org/10.1016/j.wear.2011.08.013S949927

Charakterystyka kompozytu o osnowie ceramicznej modyfikowanej włóknami węglowymi

Carbon micro/nanofibers prepared by catalytic chemical vapor deposition have been characterized in the form of powders and in the form of filaments, intercorporated in the matrix of ZrO2. Scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy, electron spectroscopy for chemical analysis and Raman spectroscopy have been used. The outer diameter of the fibers varied from 50 nm to 600 nm with an average diameter of 120 nm, length from several micrometers to several tens of micrometers and inner diameters from 20 nm to 230 nm. Two types of fibers have been identified; cylindrical which consists of a distinct graphite layers parallel to the fiber axes and bamboo - shaped fibers with walls which are built from domains with different orientations of graphite layers. The fibers contain 99.05 at.% carbon and 0.95 at.% oxygen with a binding energy of O (1s) electrons of 532.7 e V which corresponds to carbon in C-O bonds. In the first-order Raman spectra, the position of the band G was found at 1600 cm-1 and D at 1282 cm-1. The CNFs in ZrO2+ CNFs composite have been relatively well dispersed, however clusters of CNFs together with porosity are present as a result of the difficulty of dispersing, too. TEM and HREM revealed that the CNFs are usually located at the grain boundaries of ZrO2 in the form of undamaged nanofibers or disordered graphite.Włókna węglowe przygotowane metodą osadzania z par (tzw. Chemical Vapour Deposition), były badane bezpośrednio po wytworzeniu oraz po wprowadzeniu do osnowy ceramicznej metodami elektronowej mikroskopii skaningowej, transmisyjnej oraz spektroskopii ramanowskiej. Średnica włókien wahała się pomiędzy 50 nm, a 600 nm przy sredniej wartości ok.120 nm, podczas gdy ich długość wynosiła od kilku do kilkudziesięciu mikrometrów. Identyfikowano dwa rodzaje budowy włókien, tj. cylindryczne oraz z wewnętrznymi przekładkami typu „łodygi bambusa“. Włókna węglowe zawierały do 0.95 at. % tlenu o energi wiazania O (1s) ok.532.7 e V, co odpowiada wiązaniu C-O. Na pierwszym widmie Ramana pasmo G identyfikowano dla 1600 cm-1, a pasmo D dla 1282 cm-1. Badania kompozytu wykazałay równomierny rozkład włókien w ceramicznej osnowie. W sąsiedztwie większych aglomeratów stwierdzono tendencje do występowania pustek. W czasie spiekania przeważająca część włókien zachowała swoją rurkową strukturę, natomiast pozostały materiał węglowy uległ przemianie do słabo uprządkowanych struktur grafitu lub nawet uległ amorfizacji