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Salgueiredo E.,University of Aveiro | Abreu C.S.,Polytechnic Institute of Porto | Amaral M.,University of Aveiro | Oliveira F.J.,University of Aveiro | And 3 more authors.
Wear | Year: 2013

The tribological response of multilayer micro/nanocrystalline diamond coatings grown by the hot filament CVD technique is investigated. These multigrade systems were tailored to comprise a starting microcrystalline diamond (MCD) layer with high adhesion to a silicon nitride (Si3N4) ceramic substrate, and a top nanocrystalline diamond (NCD) layer with reduced surface roughness. Tribological tests were carried out with a reciprocating sliding configuration without lubrication. Such composite coatings exhibit a superior critical load before delamination (130-200N), when compared to the mono- (60-100N) and bilayer coatings (110N), considering ~10μm thick films. Regarding the friction behaviour, a short-lived initial high friction coefficient was followed by low friction regimes (friction coefficients between 0.02 and 0.09) as a result of the polished surfaces tailored by the tribological solicitation. Very mild to mild wear regimes (wear coefficient values between 4.1×10-8 and 7.7×10-7mm3N-1m-1) governed the wear performance of the self-mated multilayer coatings when subjected to high-load short-term tests (60-200N; 2h; 86m) and medium-load endurance tests (60N; 16h; 691m). © 2013 Elsevier B.V. Source

Sardinha V.M.,Center for Mechanical and Materials Technologies 2M | Lima L.L.,Center for Mechanical and Materials Technologies 2M | Lima L.L.,Institute National of S and T in Biofabrication INCT BIOFABRIS | Lima L.L.,University of Campinas | And 8 more authors.
Wear | Year: 2013

Polyvinyl alcohol (PVA) hydrogels are considered as promising biomaterials to substitute damaged articular cartilage due to their excellent biocompatibility, high permeability to fluids and low friction coefficient against smooth and wet surfaces. The study aims to demonstrate that under tribological loading mimicking in vivo conditions, PVA hydrogel/natural articular cartilage consists in a particular combination of mating surfaces with friction and wear characteristics compatible with the application as articular joints. Hydrogel membranes having approximately 1. mm thickness were processed from PVA aqueous solutions (Aldrich Mw 89000-98000. g/mol, 99% hydrolized), with 10% (w/w) concentration of polymer in solution, to be used as tribological samples against bovine articular cartilage. In order to ensure the natural properties and resistance of the tissue, articular cartilage samples were collected from condyles and prepared with ~4. mm subchondral bone. Tribological tests were performed on a pin-on-plate tribometer with a linear reciprocating geometry in the presence of distilled water and phosphate buffered saline solution (PBS) at 37. °C. The reciprocating sliding frequency and stroke length were kept constant at 1. Hz and 8. mm, respectively. Contact pressures ranging from 1. MPa to 5. MPa were applied. For each experiment the friction coefficient was determined and the dominant wear mechanisms analyzed by SEM. The topography of hydrogel membranes in the hydrated state was evaluated with AFM microscopy for quantitative and qualitative analysis of worn surfaces. Results show that PVA hydrogel present excellent tribological performance against natural articular cartilage with very low friction coefficient values (≈0.02 to 0.05) combined with the preservation of both mating surfaces. © 2012 Elsevier B.V. Source

Lima P.,Center for Mechanical and Materials Technologies 2M | Araujo M.,Center for Mechanical and Materials Technologies 2M | Mathew M.T.,Center for Mechanical and Materials Technologies 2M | Mathew M.T.,Rush University Medical Center | And 9 more authors.
Tribology International | Year: 2013

In the past few years, tribocorrosion has become a focus of research because of its relevance in terms of the future in-service degradation mechanisms of materials. In the particular case of decorative coatings, tribocorrosion is certainly one of the most important issues, and sweat corrosion and human contact wear are two other factors that may act as material selection tools. Thus, the current study aimed to investigate the tribocorrosion behavior of a new class of thin films, the Ti-C-O-N system, which is being developed to be used as a surface decorative material due to its relatively dark appearance. The films were prepared by reactive magnetron sputtering. The influence of the structural features on the tribocorrosion behavior is discussed. Source

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