Browsing by Author "Cavaleiro, A."
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- Effect of peak power on microstructure, mechanical and tribological properties of W-Ti-C-N(O) ceramic films produced by hybrid sputteringPublication . Ataie, S.A.; Soltanieh, M.; Naghizadeh, R.; Cavaleiro, A.; Fernandes, F.; Ferreira, F.This research investigates the impact of peak power (from 44 to 105 kW) on the structural and tribological properties of W-Ti-C-N(O) films. Chemical analysis of the coatings, using energy-dispersive spectroscopy and Raman spectroscopy, indicates that increasing target power results in a rise in the oxygen (from 2.6 to 12.0 at%), carbon (from 19.7 to 32.4 at%), and sp3 (from 9.8% to 24.3%) content. Morphological and topographical analysis reveal that an increase in target power causes a transition from a columnar structure (with nodular grains) to a dense structure (with textured grains). The indentation and dry sliding tests demonstrate that the maximum level of H/E2 (0.00047 GPa-1) is achieved, along with a low wear rate of 8.1 × 10-7 mm3/N.m.
- Effect of substrate bias voltage on structural and tribological properties of W-Ti-C-N thin films produced by combinational HiPIMS and DCMS co-sputteringPublication . Ataie, S.A.; Soltanieh, M.; Naghizadeh, R.; Cavaleiro, A.; Evaristo, M.; Fernandes, F.; Ferreira, F.Protective multi-component thin films at the surface of cutting tools have been significantly developed to reduce wear and friction. The present work investigates the effect of substrate bias voltage on the structural-tribological relations of W-Ti-C-N thin films produced by HiPIMS and DCMS co-sputtering. Chemical analysis of the coatings is obtained and composite phase structure is revealed. Morphology of the coatings illustrates that defectless surfaces may be achieved. Topographical parameters are investigated by employing graphical software. Indentation, scratch and pin-on-disk tests (pin is AISI 52100 steel) are applied to study mechanical behaviors of the films. To produce a wear-resistant film, a median bias voltage ( 60 V) and as a result, optimum content of tungsten concentration (19.2 at. %), grain size (42.8 nm) and average peak interval (188 nm) is required. Finally, a model based on the representative volume element is developed to show crack propagation and delamination.
- Room and high temperature tribological performance of CrAlN(Ag) coatings: The influence of Ag additionsPublication . Rajput, S.S.; Gangopadhyay, S.; Yaqub, T.B.; Cavaleiro, A.; Fernandes, FilipeThe present study aims to investigate the effect of the addition of Ag on the tribological performance of a CrAlN coating system, at room and high temperatures (600 °C). The addition of Ag, in general, has been seen beneficial in lowering the coefficient of friction (COF) at room and high temperatures. Independent of the decrease of COF with Ag additions, the specific wear rate was degraded. The only exception was the CrAlNAg9 coating with 8.6 at.% of Ag which exhibited the lowest specific rate at room temperature while maintaining its comparable wear resistance properties with that of reference CrAlN coating at 600 °C. The CrAlNAg9 coating also demonstrated coefficient of friction (COF) of 0.16 and 0.26 at room temperature and 600 °C, respectively. Formation of Ag and AgCrO2-rich tribolayer during sliding at high temperature was responsible for lubricious properties of CrAlN(Ag) coatings. However, doping the coatings with small content of Ag (around 2.4 at.%) was not effective in decreasing the COF, nor the specific wear rate under high temperatures. On the other hand, high concentration of Ag (11.8 at.% and above) had a detrimental influence on mechanical properties and poor resistance to oxidation at elevated temperature compromising both friction and wear properties of the CrAlNAg12 and CrAlNAg16 coatings.
- The influence of V addition on the structure, mechanical properties, and oxidation behaviour of TiAlSiN coatings deposited by DC magnetron sputteringPublication . AL-Rjoub, A.; Yaqub, Talha Bin; Cavaleiro, A.; Fernandes, FilipeThe influence of V content on the morphology, structure, hardness (H) and reduced Young's modulus (E), adhesion, and oxidation resistance of TiAlSiN coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing V contents from 0, 4.8 and 11.0 at.%. All coatings exhibit a fcc type structure. The coating with 4.8 at.% of V shows the highest values of H and E, whereas the values are similar for the reference coating and the coating with 11.0 at.% of V. The coatings adhere well to the substrates and show a dense and compact columnar growth extending from the adhesive interlayer to the top surface of the coatings. The dynamic thermal gravimetric oxidation curves reveal that V additions decreases the onset point of oxidation significantly and degrades the oxidation resistance of the coatings. A dual oxide layer is formed on the top surface of the reference coating: an outer porous Ti–Al–O rich layer with plate-like features on the top, which classified to TiO2 (rutile and anatase) and Al2O3 phases, and an inner Ti–Si–O rich layer with Al depletion that identified as mixture of amorphous Si–O and Ti–Si–O protective oxides. The diffusion of V to the top surface governs the oxidation process of the V-containing coatings, i.e. increasing V concentration leads to disrupt the formation of the protective continuous oxide layers easily.
- The role of interfaces and morphology on silver diffusion in hard coatingsPublication . Cavaleiro, D.; Munnik, F.; Krause, M.; Carbo-Argibay, E.; Ferreira, P.J.; Cavaleiro, A.; Fernandes, F.One of the main approaches to increase the tool lifetime during dry machining of “hard-to-machine” aerospace alloys is self-lubrication by the incorporation of noble metals in hard matrixes with good mechanical and diffusion barrier properties. In this paper, the diffusion of an Ag-rich layer sandwiched between two layers of either TiN or TiSiN is studied by transmission electron microscopy and in situ Rutherford backscattering spectrometry. The layer stacks were subjected to annealing treatments at 600 ◦C and 800 ◦C for 2 hours. Three processes were found to control the diffusion of silver: the morphology of the “sandwich” layers, the formation of small voids in the involved interfaces and the sublimation of Ag in the surface at temperatures near the melting point. The study revealed that the dense TiSiN matrix allowed a significantly better control of Ag diffusion than the more open TiN matrix.