1,721,116 research outputs found
Tribological properties of HVOF as-sprayed and heat treated Co–Mo–Cr–Si coatings
No full textHVOF-sprayed Co–28%Mo–17%Cr–3% Si alloy tribological performance was tested in the as-sprayed condition and after thermal treatments at 200, 400, 600°C for 1 h. As-sprayed coating possesses low hardness, undergoes adhesive wear against 100Cr6steel and displays an high-friction coefficient causing relevant thermal effects. The 600°C-heat treatment increases microhardness, thus preventing adhesive wear and reducing friction
Heat Treatment Effects on the Tribological Performance of HVOF-Sprayed Co-Mo-Cr-Si Coatings
No full textThe tribological behavior of high-velocity oxyfuel sprayed Co-28%Mo-17%Cr-3%Si coatings, both as sprayed and after heat treatments at 200, 400, and 600 °C for 1 h, has been studied. The as-sprayed coating contains oxide stringers and is mostly amorphous. It has low hardness (∼6.7 GPa) and toughness and undergoes adhesive wear against 100Cr6 steel. The friction coefficient increases up to ∼0.9, so the flash temperature reaches a critical oxidation value; then, friction decreases and increases again. This phenomenon occurs periodically. Much adhesive wear occurs in the first stage. Abrasive wear prevails against alumina pin: the coating wear rate is lower because it possesses good plasticity. Thermal effects still occur. The 600 °C treatment causes formation of submicrometric crystals. Hardness increases (∼8.8 GPa), adhesive wear is prevented, the friction coefficient has no peaks. Against the alumina pin, wear rates remain similar to the as-sprayed case. Nevertheless, the friction coefficient has no peaks and its final value is lowered (from 0.84 to0.75)
Metodo e dispositivo per la prova di file endodontici
Full text linkRIASSUNTO
Sono descritti un metodo, ed un dispositivo
per l’attuazione di detto metodo, per realizzare
prove di fatica, su file endodontici (2) rotanti o 5 reciprocanti in leghe Ni-Ti a memoria di forma.
Il metodo è del tipo che prevede l’inserimento di detto file (2) in canali artificiali (3), ed è caratterizzato dal fatto di effettuare:
- prove di fatica statica, ponendo in rotazione
10 detto file (2) e obbligandolo a deformarsi ciclicamente ad ogni rotazione del file (2) stesso; - prove di fatica dinamica, mediante un inserimento del file (2) in profondità in un canale (3), detta placchetta (4) venendo allontanata e
15 riavvicinata di una corsa predefinita.
Il dispositivo è del tipo che comprende uno o
più canali artificiali (3), ed è caratterizzato dal fatto di comprendere:
- primi mezzi (5) atti a posizionare il file (2)
20 rispetto a detti canali artificiali (3);
- secondi mezzi (6) atti a fare in modo tale che il file (2) entri ed esca da detti canali (3), per effettuare una prova di fatica dinamica;
- terzi mezzi (7) per imprimere al file (2) un moto
25 rotatorio, per effettuare una prova di fatica statica.
Microstructural analysis of high-pressure cold-sprayed Ni, NiCu and NiCu+Al2O3 coatings
No full textCold spraying has shown its potential to produce metallic and composite coatings with high quality and performance. For instance, the impermeability of the coatings is the criterion for the corrosion resistance and thus, fully dense coatings can act as real corrosion barrier coatings. Our previous study has demonstrated the good corrosion properties of high-pressure cold-sprayed (HPCS) Ni and NiCu coatings whereas the present study focuses on the analysis of structural characteristics behind the dense coatings. Microstructures of as-sprayed and heat-treated HPCS Ni, Ni20Cu and Ni20Cu + Al2O3 coatings have been evaluated with FESEM from top-view direction. This revealed clearly particle deformation and particle boundaries whereas particle bonding was evaluated with cavitation–erosion test. Density was proven with Corrodkote test and impermeable HPCS NiCu + Al2O3 coating structures were achieved. Furthermore, cavitation–erosion resistance of NiCu coating was improved by heat treatment
Wear behaviour of thermally sprayed ceramic oxide coatings
No full textThe wear resistance of plasma-sprayed ceramic coatings (Al2O3, Al2O3-13%TiO2, Cr2O3) has been investigated through pin-on-disk and dry sand-steel wheel tests, has been correlated to microstructural and micromechanical characteristics (microhardness, fracture toughness) and has been compared to well-known platings (such as Cr electroplating and electroless Ni) and HVOF-sprayed cermets (WC-17%Co, WC-10%Co-4%Cr). Plasma-sprayed ceramics are hard but brittle: dry particles abrasion occurs through splats detachment. The toughest coating (Al2O3) displays the highest wear resistance, which in fact overcomes HVOF-sprayed cermets and Cr electroplating, when a low number of wheel revolutions are considered. In pin-on-disk tests, no coating undergoes wear loss against the 100Cr6 ball, that possess lower hardness. Against the alumina ball, Al2O3 and Al2O3-TiO2. coatings show high wear rates and friction coefficients (due to chemical affinity), while Cr2O3 possesses better wear resistance, lower friction coefficient and inflicts less wear on the counterpart. Cr2O3 wear scar consists in plastically deformed splats and debris forming a quite adherent protective tribofilm. (c) 2006 Elsevier B.V. All rights reserved
Corrosion resistance of HVOF-sprayed coatings for hard chrome replacement
No full textHVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) and electrolytic hard chrome (EHC) coatings corrosion resistances have been compared through electrochemical polarization tests (0.1 N HCl, 0.1 N HNO3) and Corrodkote test. EHC coatings passivate in HNO3, but undergo pitting corrosion in HCl and in Corrodkote test too. HVOF coatings do not passivate, but possess more noble corrosion potentials. Both in HNO3 and HCl, they undergo more generalized corrosion, with similar i(corr); crevice corrosion along splat boundaries is sometimes detected after the HCl test. Their i(corr) in 0.1 N HCl solution is lower than in several of EHC coatings. No visible damage in the HVOF coatings has occurred after the Corrodkote test. (c) 2006 Elsevier Ltd. All rights reserved
On the combined use of scratch tests and CLA profilometry for the characterization of polyester powder coatings: influence of scratch load and speed
No full textThe prediction of the mechanical properties of polyester powder coatings is of paramount importance, asthey have to undergo a wide variety of forces and deformations during their service life. Determine theresponse of polymeric coatings to the actual loading conditions can be, however, very troublesome astheir properties are function of the material physical state, rate-dependence and yield and breakbehaviour. Further, the characterization of soft, contaminated organic surfaces such as polymers canoften cause severe problems with reliability and imaging accuracy due to instrumental artefacts.This is therefore the context in which this paper investigates the capability of multiple parametersscratch tests joined with non-contact CLA profilometry and FE-SEM to detect the scratch response ofpolyester powder coatings for protective and decorative outdoor applications. Scratch tests with bluntcontact geometry were used to evaluate the response of polyester coatings baked at different time–temperature programs and, so, at different stages of their curing process. In particular, being suchcoatings highly non-linear in their response tomechanical stress or strain, the influence from scratch load and speed was carefully taken into account. Analytical evaluations of the experimental results led to goodcorrelations between the extent of the deformed zone after scratch, scratch parameters and curingoperational settings. This allows mapping the scratch response of the polyester topcoats to broad rangesof both scratch parameters and curing conditions
Electrochemical comparison between corrosion resistance of some thermally sprayed coatings
No full textElectrochemical polarisation and impedance spectroscopy tests in0.1 M HCl and 0.1 M H2SO4 solutions were performed on HVOF-sprayedcermet coatings (WC–17% Co, WC–10% Co–4% Cr) and AtmosphericPlasma-Sprayed (APS) ceramics (Al2O3, Al2O3–13 wt%TiO2, Cr2O3) with APSbond coat (Ni–Co–Cr–Al–Y). Reference tests were also performed on hardchrome electroplating. Plasma-sprayed coatings offer limited substrateprotection owing to interconnected porosity, although the bond coat promotessome forms of passivation in H2SO4. HVOF-sprayed cermets possess goodcorrosion resistance in both environments. Chrome electroplating showscomparatively better corrosion resistance in H2SO4, but worse in HCl
Corrosion resistance of cold-sprayed Ta coatings in very aggressive conditions
No full textThis study deals with the corrosion behaviour of high-pressure cold-sprayed Ta coatings, compared with Tabulk material and inert-atmosphere plasma-sprayed Ta coatings. Electrochemical polarization andelectrochemical impedance spectroscopy measurements are carried out in 1 M KOH solution; immersiontests are performed in 1 wt.% HF solution, and the resistance to high-temperature oxidation and molten saltattack is evaluated by hot corrosion tests. Moreover, the effect of substrate material (steel, Al and Cu) on thecoating formation is investigated using FESEM
Plasma-sprayed graded ceramic coatings on refractory materials for improved chemical resistance
No full textPlasma-sprayed ceramic coatings were manufactured on sintered alumina-mullite refractory bricks to improve their chemical resistance to molten glass. Mullite and alumina powders were employed. Graded layered coatings were designed and produced, to reduce the thermal expansion mismatch with the substrate: in all cases, the upper layer consisted in pure alumina (very resistant to chemical attack); alumina-mullite intermediate layers were added to match the low thermal expansion of the porous substrates. Plasma-sprayed coatings definitely improved both the abrasion resistance and the chemical resistance to long-time (8 h at 1400 degrees C) contact with molten glass, since the coating preserved its original microstructure. However, in thermal shock tests, some transverse cracks appeared; thus, thermal cycling tests in presence of molten glass indicated that, after a few cycles, the glass can penetrate down to these cracks. The tested samples were studied by means of scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD)
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