317 research outputs found

    Small-scale mechanical response at intermediate/high temperature of 3D printed WC-Co

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    The present work is focused on WC-Co dry-electropolished. A systematic nanomechanical study of a 3D printed WC-Co grade is investigated. In doing so, nanoindentation technique is implemented and the main deformation/damage mechanisms induced at the submicrometric lenght scale are investigated at different temperatures, from room up to 600ºC. In general, three different approaches are followed to accomplish this research: (1) assessment of intrinsic hardness values as a function of crystallographic orientations from a room temperature up to 600ºC and (2) the determination of effective hardness and flow stress through the Tabor's equation of the metal cobalt binder. Finally, the elastic strain to break was also determined for the main crystallographic orientations for the WC particles as a function of the temperature. The preliminary results highlight that the strenght reduction with increasing temperature is attributed to metallic binder softening. On the other hand, the WC particles presents an isotropic behavior when the testing temperature is over 500ºC because, to inside these particles, the dislocations and the stacking faults are the main deformation mechanisms induced at intermediate/high testing temperature.Postprint (published version

    Influence of pre-existing martensite on the wear resistance of metastable austenitic stainless steels

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    The effect of pre-existing martensite on the sliding wear behavior of a commercial metastable austenitic stainless steel was investigated. Two different steel conditions were considered: annealed (with a fully austenitic microstructure) and cold rolled, consisting of mixtures of austenite and martensite. Wear tests were carried out using ball on disc technique at constant velocity and different sliding distances. Correlation between microstructure and wear mechanisms was performed by X-ray diffraction, electron back-scattered diffraction and focus ion beam. Results show that wear resistance decreases at increasing the amount of pre-existing martensite. In this sense, more strain-induced martensite developed for cold rolled samples, hardening the surface and consequently reducing wedge formation, which induced material removal from the surface. The detailed analysis of the wear track demonstrated the formation of an ultrafine-grain layer just below the surface, not only for annealed but also for cold rolled steel.Peer ReviewedPreprin

    ElectroCatalytic Activity of Nickel Foam with Co, Mo, and Ni Phosphide Nanostructures

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    In this study, the electrocatalytic activity of nickel foam, which is activated by cobalt, molybdenum, and nickel phosphide nanostructures, is prepared by the plasma hydrothermal method for use in the release of hydrogen and oxygen. The morphology and crystallographic structure of the synthesized phosphide specimens were examined by means of scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. Moreover, the electrolysis activity for these sets of specimens was investigated using the Tafel polarization curve or linear sweep voltammetry, cyclic voltammetry, as well as by means of the electrochemical impedance spectroscopy technique. Preliminary results show that nickel phosphide presents the highest electrocatalytic activity than the other phosphides developed in this research. In this regard, it presents an electrocatalytic activity to release hydrogen and oxygen of around -1.7 and 0.82 mV, which is measured at a current density of 100 mA·cm-2, respectively.Peer ReviewedPostprint (published version

    Exploring the effects of laser surface modification on AISI 301LN steel: a micro-mechanical study

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    This article investigates the surface hardening capability of a metastable austenitic TRansformation Induced Plasticity (TRIP) stainless steel, particularly on AISI 301LN, by laser texturing. This technology produces microstructural surface changes in terms of both phase transformation and grain size modification and, as a direct consequence, the laser influences the surface characteristics, mainly hardness and roughness. In this sense, the key parameters (laser power, scanning speed and position of the focal length) were investigated by using a Design of Experiments (DoE) in detail to better understand the correlation between texturing parameters, microstructural and mechanical changes, always at the superficial level. From all the aforementioned information, the results show that the maximum surface hardening is obtained by increasing the laser power and decreasing the scanning speed. Furthermore, by reducing the focal distance, the depth of the microstructural evolution layer is more significant, while the width is less affected. Finally, a suitable model was developed to correlate the processing parameters here investigated with the resulting surface integrity, in terms of mechanical properties, by means of a regression equation.This research was funded by AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca), grant number FI-SDUR 2020.Peer ReviewedPostprint (published version

    Can the DryLyte® Technology Polish 3D Printed Ceramic/Metal Samples and in Particular WC-Co?

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    DryLyte® Technology is an effective surface finish technique, which follows the same traditional electrolytic cell principle, but uses an electrolytic solid non-conductive medium rather than a liquid one. For the last 10 years, this technology has been attracting a lot of attention compared to conventional ones due to the selective smoothing of the surface technique, interacting only with the roughness peaks and not with the valleys, etc. In this book’s chapter, for 3D-printed cemented carbides (WC-Co) polished with DryLyte® Technology, it is shown the correlation between the microstructure and the surface integrity, in terms of mechanical properties, at submicrometric length scale. Also, a particular case study is presented of 3D-printed WC-Co as a function of the testing temperature, ranging from room temperature up to service-like working conditions. Finally, the mechanical properties are correlated as function of the chemical nature and/or crystallographic phase

    Effect of laser surface texturing on Schmid factor and plastic deformation mechanisms on AISI 301LN steel

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    In this comprehensive study, the multifaceted impact of laser surface texturing (LST) on AISI 301LN stainless steel is explored. Changes in the microstructure, mechanical properties, and grain characteristics are examined. The dynamic relationship between Schmid factor evolution and plastic deformation in this stainless steel alloy is unveiled through the analysis of grain statistics and individual grain scrutiny. It is revealed that LST initiates the formation of strain-induced a’-martensite, grain refinement, and substantial hardness enhancements. Notably, an a’-martensite crystalline size of 2.05 Å is induced by LST. Furthermore, a 12% increase in tensile strength is observed after LST along with an 11% boost in yield strength. However, reductions of 19% in elongation to fracture and 12% in the area reduction are experienced.This research was funded by AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca), grant number FI-SDUR 2020.Peer ReviewedPostprint (published version

    Phase transformation and residual stresses after laser surface modification of metastable austenitic stainless steel

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    Laser surface modification treatments have been applied to samples of a metastable austenitic stainless steel AISI 301LN. The amount of residual stresses and the presence of induced a´-martensite phase on the surface and subsurface of the samples, as a consequence of laser modification, have been investigated in this study. X-ray diffraction has been used to measure these values, which is a non-destructive method. Laser modification has been applied as parallel lines at a distance of 40 µm, using a laser intensity of 4 A and scanning speeds of 1, 3, and 5 bits/ms, frequency had a constant value of 1000 Hz. The results of the phase analysis show an increase in the a´-martensite present in the surface modified by the laser and that the sample corresponding to the lowest laser speed has the highest martensite fraction. Also, high tensile residual stresses were generated, more pronounced for the lowest laser scanning speed.Peer ReviewedPostprint (published version

    Surface grain size and texture after annealing ground zirconia

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    The surface microstructure induced after grinding and annealing 3 mol% Y2O3 stabilized tetragonal zirconia was investigated in a range of annealing temperatures between 1200 and 1600 °C. For annealing temperatures close to 1200 °C, a surface nano-grain size layer was formed, while annealing at 1600 °C induced a very high fraction of surface grains of size and yttrium content higher than the bulk. The use of TEM-EBSD observation along the surface of the specimen ground and annealed at 1200 °C also revealed the existence of a (0 1 0) preferential orientation.Peer ReviewedPostprint (author's final draft

    Small scale fracture behaviour of multilayer TiN/CrN systems: Assessment of bilayer thickness effects by means of ex-situ tests on FIB-milled micro-cantilevers

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    TiN/CrN multilayered PVD coatings are known to exhibit outstanding micromechanical properties and wear resistance. On the other hand, information on their small scale fracture behaviour is rather scarce. The present work aims to address it by testing to failure FIB-milled microbeams of multilayer TiN/CrN systems with different bilayer periods (8, 19 and 25 nm). In doing so, these micrometric specimens are first FIB notched, and thus deflected by means of a nanoindentation system. It is found that multilayer architecture translates into a beneficial synergic effect regarding critical load for reaching unstable failure; and thus, on energy absorption at fracture. Such behaviour is associated with small scale crack deflection as main toughening mechanism.Peer ReviewedPostprint (author's final draft
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