Tribological performance of Graphene/Carbon nanotube hybrid reinforced Al2O3 composites

Tribological performance of the hot-pressed pure Al2O3 and its composites containing various hybrid contents of graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) were investigated under different loading conditions using the ball-on-disc method. Benchmarked against the pure Al2O3, the composite reinforced with a 0.5 wt% GNP exhibited a 23% reduction in the friction coefficient along with a promising 70% wear rate reduction, and a hybrid reinforcement consisting of 0.3 wt.% GNPs + 1 wt.% CNTs resulted in even better performance, with a 86% reduction in the wear rate. The extent of damage to the reinforcement phases caused during wear was studied using Raman spectroscopy. The wear mechanisms for the composites were analysed based on the mechanical properties, brittleness index and microstructural characterizations. The excellent coordination between GNPs and CNTs contributed to the excellent wear resistance property in the hybrid GNT-reinforced composites. GNPs played the important role in the formation of a tribofilm on the worn surface by exfoliation; whereas CNTs contributed to the improvement in fracture toughness and prevented the grains from being pulled out during the tribological test

Hardness and elasticity of abrasive particles measured by instrumented indentation

Basic mechanical properties of seven types (from seven different sites) of abrasive garnet particles used for water jet cutting were measured using the technique of instrumented indentation (also called depth sensing indentation or nanoindentation). Hardness and modulus of elasticity were evaluated and compared. All the abrasives had similar measured mechanical properties (hardness 20 – 24.16 GPa), the highest values were found for the Czech garnet

Fatigue behaviour of mullite studied by the indentation flexure method

A systematic study has been performed of the use of the Indentation Flexure Fatigue (IFF) method to study crack growth in mullite at room temperature and high temperature (1300°C). The results obtained for a mullite have been compared with previous data generated on the same material, but using the more direct compact tension method. The material produces transgranular crack growth and consequently does not show R-curve behaviour, which considerably simplifies the comparison of the data generated by both methods. The IFF method can significantly overestimate the crack tip stress intensity factor because of the way in which the residual stress intensity produced by the indentation is estimated. The experimental details that influence the test results were investigated.This work was supported by the Royal Society NATO Fellowship, which financed stay of P. Hvizdoš at QMW College, London. We would also like to thank F. Guiu, C. K. L. Davies, G. Fantozzi and C. Olagnon for their discussions during the Brite-Euram project.Peer reviewe

The Study of Selected Properties of Ti EB PVD Coating Deposited Onto Inner Tube Surface at Low Temperature

This study investigates the selected properties of the thin Ti coating applied by activated evaporation EB PVD technique. This technique was used for the deposition of Ti thin coating onto inner surface of OKhN3 MFA steel tubes. Deposition process was carried out at temperature 200°C. Conventional type of coatings - monolayer Ti - was analyzed by standard techniques for surface status and quality assessment - coating thickness, chemical composition by EDX analysis, adhesion, hardness, roughness, and growth direction of columns at room temperature. Ti monolayer achieved roughness Ra equal from 0.42 μm to 0.47 μm. The resulting hardness was from 2 GPa to 8.5 GPa depending on the sample location inside the vacuum chamber. Placing of the coated surface also affected the direction of grain growth of Ti coating columns. The angles α of grain growth were found to be from 40° to 60°. Angle α increased two to three times more than the incidence angle β (from 12° to 28°) of evaporated Ti particles. Values of the adhesion measured along the Ti growth direction were mostly higher (up to 10%) or the same as those measured perpendicular to it