Surface texturing of aluminium alloy AA2024-T3 by picosecond laser: Effect on wettability and corrosion properties

The effects of laser texturing on the corrosion and wettability of AA2024-T3 using an IR Nd:Vanadate picosecond (ps) laser was studied. Three types of texture patterns were generated: dimples with 5% and 50% area density (percentage of surface area textured); cross groove patterns with an area density of 64%; and concentric ring patterns with an area density of 70%. For the higher area densities, the surface character changed from hydrophilic to hydrophobic. The evolution of the open circuit potential over time, potentiodynamic polarization curves and electrochemical impedance spectroscopy were then investigated and analysed. The results revealed that ultrashort ps laser surface texturing did not modify the corrosion behaviour of AA 2024-T3 in the test solution.This work was supported by the Spanish Ministry of Science and Innovation [SMOTI MAT2009-13751] and the Spanish Ministry of Economy and Competitiveness [MAT2013-48224-C2-1-R-MUNSUTI].Peer Reviewe

Corrosion resistance of anodic layers grown on 304L stainless steel at different anodizing times and stirring speeds

Different chemical and physical treatments have been used to improve the properties and functionalities of steels. Anodizing is one of the most promising treatments, due to its versatility and easy industrial implementation. It allows the growth of nanoestructured oxide films with interesting properties able to be employed in different industrial sectors. The present work studies the influence of the anodizing time (15, 30, 45 and 60 min), as well as the stirring speed (0, 200, 400, and 600 rpm), on the morphology and the corrosion resistance of the anodic layers grown in 304L stainless steel. The anodic layers were characterized morphologically, compositionally, and electrochemically, in order to determine the influence of the anodization parameters on their corrosion behavior in a 0.6 mol L-1 NaCl solution. The results show that at 45 and 60 min anodizing times, the formation of two microstructures is favored, associated with the collapse of the nanoporous structures at the metal-oxide interphace. However, both the stirring speed and the anodizing time have a negligeable effect on the corrosion behavior of the anodized 304L SS samples, since their electrochemical values are similar to those of the non-anodized ones

Microestructura y propiedades de capas de tribaloy T-800 depositadas mediante plaqueado láser

RESUMEN: El presente trabajo se centra en la obtención de capas de aleación base Cobalto (Tribaloy T-800) sobre un sustrato de acero inoxidable 18/8 (AISI 304) mediante la técnica de plaqueado láser. Tras los tratamientos, se caracterizaron las probetas mediante microscopía óptica y electrónica de barrido con microanálisis (EDS). La composición elemental del recubrimiento se determinó en un espectrómetro de emisión óptica con fuente de excitación (GDL). El estudio de la interfase reveló una perfecta adherencia entre el recubrimiento y el material base, sin defectos apreciables. La microestructura de las capas depositadas es dendrítica con un alto grado de refinamiento y una homogeneidad química a lo largo del cordón y con valores muy próximos a los del polvo de partida. En las zonas de solape entre cordones, se observó un crecimiento del grano debido al segundo tratamiento térmico recibido. La microdureza de las capas alcanza los 750 HV, valor considerablemente superior al del sustrato (200 HV). Asimismo, se obtuvo una mejora significativa de la resistencia a la corrosión del recubrimiento en medios salinos.ABSTRACT: The present work is based on obtaining Co based coatings (Tribaloy T-800) on plates of 18/8 stainless steel (AISI 304) by laser cladding technique. After the treatment, samples were characterized by optical and scanning electron microscopy with EDS analysis. The elemental composition of the coating was determined with a glow discharge lamp spectrometer (GDL). The study of the interface revealed a good adherence between the substrate and coating without substantial defects. For the laser cladded coatings, the microstructure was dendritic with a high degree of refinement and chemical homogeneity close to the original powder. The grain coarsening was observed in the overlapping zones due to the second heat treatment. Microhardness of the coatings reached 750 HV, a considerably higher value than the substrate hardness (200 HV). Also, the coating corrosion resistance in saline solutions had a great improvement

Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the "race for the surface" theory

Objectives Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the 'race for the surface' theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied. Methods We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis. Results Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria. Conclusions The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence.This work was funded by the following grants from the Spanish MINECO (MAT2013- 48224-C2-2-R and MAT2013-48224-C2-1-R). M. Martínez-Pérez reports funding received from EFORT 2015 congress: travel supported by PFIZER, which is related to this article. J. Esteban and E. Gómez-Barrena report funding received from several companies for travel, expenses and grants, none of which is related to this articl

The effect of laser transformation notching on the controlled fracture of a high carbon (C70S6 ) steel

A high carbon (C70S6) steel has been laser surface treated using CO2 and Diode lasers in order to produce an embrittled region to act as a fracture notch. Such a process has been investigated as a precursor to the fracture splitting of automotive engine connecting rods. Microstructures of the treated regions have been examined and the fracture behaviour of notched samples has been quantified. Depending on the laser processing parameters used, the laser transformation notch (LTN) undergoes either solid state transformations or a mixture of melting and solid state transformations. The effect of LTN depth on the peak impact force, the crack initiation energy and Charpy fracture energy was investigated on a C70S6 carbon steel using an instrumented Charpy impact facility. It was reduced to a value < 3.5 J by a LTN of ~ 0.5 mm in depth. Fracture mechanics models indicate that such a LTN can behave in a similar way to a fatigue created crack used in fracture toughness testing ie the LTN behaves as a sharp crack. Obtaining a sharp crack effect from a LTN is attributable to a combination of: a) the presence of brittle martensite, b) intergranular cracking of favourably oriented columnar grains after melting with inclusions and defects at their boundaries, c) intergranular cracking of coarse grains produced by a high austenitising temperatures and d) minor or major cracks sometimes resulting in centre – line cracking which arises during solidification. LTN was thus shown to have the potential to lead to an effective means of obtaining consistent fracture splitting of connecting rods

Dwell-time distributions in quantum mechanics

Some fundamental and formal aspects of the quantum dwell time are reviewed, examples for free motion and scattering off a potential barrier are provided, as well as extensions of the concept. We also examine the connection between the dwell time of a quantum particle in a region of space and flux-flux correlations at the boundaries, as well as operational approaches and approximations to measure the flux-flux correlation function and thus the second moment of the dwell time, which is shown to be characteristically quantum, and larger than the corresponding classical moment even for freely moving particles.Comment: To appear in "Time in Quantum Mechanics, Vol. 2", Springer 2009, ed. by J. G. Muga, A. Ruschhaupt and A. del Camp

Mochras borehole revisited: a new global standard for Early Jurassic earth history

The Early Jurassic epoch was a time of extreme environmental change: there are well-documented examples of rapid transitions from cold, or even glacial, climates to super greenhouse events, the latter characterized worldwide by hugely enhanced organic carbon burial, multiple large isotopic anomalies, global sea-level change, and mass extinction (Price, 1999; Hesselbo et al., 2000; Jenkyns, 2010; Korte and Hesselbo, 2011). These icehouse–greenhouse events not only reflect changes in the global climate system but are also thought to have had significant influence on the evolution of Jurassic marine biota (e.g. van de Schootbrugge et al., 2005; Fraguas et al., 2012). Furthermore, the events may serve as analogues for present-day and future environmental transitions